JP2011077775A - Image processing apparatus, image output device, image processing method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus or the like for improving the appearance of the details of images when compressing colors. <P>SOLUTION: The image processing apparatus includes: a color compression unit for compressing brightness components and saturation components by a compression ratio of the brightness components and the compression ratio of the saturation components compliant with the hue components of the image data on the basis of the color gamut of an input image and the color gamut of the image output device; a brightness component correction amount calculation unit for calculating the correction amount of the brightness component compliant with the compression ratio of the brightness component for the image data of a given spatial frequency band; a saturation component correction amount calculation unit for calculating the correction amount of the saturation component compliant with the compression ratio of the saturation component for the image data of the given spatial frequency band; a brightness component correction unit for correcting the compressed brightness component using the correction amount of the brightness component; and a saturation component correction unit for correcting the compressed saturation component using the correction amount of the saturation component. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, an image output apparatus, an image processing method, a program, and the like.

  Image display devices and image printing devices as image output devices are limited in the range of colors that can be output. For this reason, the image output apparatus cannot reproduce all colors that can be recognized by the human eye. The color gamut, which is the color range, varies depending on the type of the image output device, and images of various color gamuts such as sRGB (standard RGB) and Adobe RGB can be input to the image output device. Therefore, the color gamut of the input image may be different from the color gamut of the image output device. When the color gamut of the image output device is narrower than the color gamut of the input image, a process called color compression is performed. It is done to compress the colors. Also, when the color gamut of the image output device is wider than the color gamut of the input image, the color is expanded within the color gamut of the image output device by a process called color expansion.

  The color compression process and the color expansion process are disclosed in Patent Document 1. This patent document 1 compares the color gamut of an input image with the color gamut of an image output device, and performs color compression for a hue whose input image has a larger color gamut than the color gamut of the image output device. An image processing method is described in which a hue whose input image has a smaller color gamut than the color gamut is subjected to color expansion opposite to color compression. In this image processing method, when the input image is divided into a plurality of regions, the above-described processing is performed for each region, and the compression rate at the time of color compression and the expansion rate at the time of color expansion become higher in the high saturation region. Is processed as follows.

JP 2000-83177 A

  However, with the technique disclosed in Patent Document 1, the higher the saturation region, the higher the compression rate during color compression and the expansion rate during color expansion. For this reason, as in a general color compression process, there is a problem that, in a high saturation area, the color change becomes small during color compression, and the details of the image are crushed. Further, the technique disclosed in Patent Document 1 has a problem in that there is a region where the compression rate is partially increased in the high brightness region, and the details of the image are expressed in a collapsed state during color compression.

  The present invention has been made in view of the above technical problems. According to some aspects of the present invention, it is possible to provide an image processing device, an image output device, an image processing method, a program, and the like that improve the appearance of image details when color compression is performed.

  (1) According to one aspect of the present invention, an image processing device that corrects image data supplied to an image output device uses the image data based on a color gamut of an input image and a color gamut of the image output device And compressing the lightness component of the image data with the compression ratio of the lightness component of the image data corresponding to the hue component of the image data, and the saturation of the image data with the compression ratio of the saturation component of the image data corresponding to the hue component A color compression unit that compresses the component, and a lightness component correction amount calculation unit that calculates the correction amount of the lightness component of the image data according to the compression ratio of the lightness component for image data in a given spatial frequency band A saturation component correction amount calculation unit that calculates, for image data in a given spatial frequency band, a saturation component correction amount of the image data according to a compression rate of the saturation component, and the lightness Using the component correction amount, the color compression And a saturation component for correcting the saturation component of the image data compressed by the color compression unit using the correction amount of the saturation component. And a component correction unit.

  In this aspect, based on the color gamut of the input image and the color gamut of the image output device, the lightness component and the saturation component of the image data are compressed at a compression rate corresponding to the hue component of the image data. At this time, for the image data in a given spatial frequency band, the brightness component of the image data is corrected in accordance with the compression ratio at the time of the above compression processing, so that it was lost due to the compression of the brightness component. By correcting the portion, it is possible to improve the appearance of the detail portion of the image that is lost on the high lightness side during color compression. Similarly, with respect to image data in a given spatial frequency band, the saturation component of the image data is corrected according to the compression ratio at the time of the above compression processing, so the compression of the saturation component is performed. By correcting the lost portion, the appearance of the detail portion of the image lost on the high saturation side during color compression can be improved.

  (2) An image processing apparatus according to another aspect of the present invention is based on a color gamut of the input image and a color gamut of the image output apparatus, and compresses the lightness component and the color according to the hue component. A compression rate calculation unit that calculates a compression rate of the brightness component, and the color compression unit compresses the brightness component of the image data with the compression rate of the brightness component calculated by the compression rate calculation unit, and The saturation component of the image data is compressed with the compression rate of the saturation component calculated by the compression rate calculation unit.

  According to this aspect, since the compression rate is calculated based on the color gamut of the input image and the color gamut of the image output device, in addition to the above effects, the lightness component and the saturation of the input image data Optimum correction can be performed on the components, and it is possible to contribute to high image quality of the image after color compression.

  (3) In the image processing apparatus according to another aspect of the present invention, the lightness correction curve in which the compression rate calculation unit indicates the relationship between the lightness component Lin before color compression and the lightness component Lout after color compression, As the component compression rate, the reciprocal of the slope ΔLin / ΔLout in the lightness component Lin is calculated.

  According to this aspect, since the compression rate in the color compression processing performed according to the lightness correction curve can be faithfully reflected in the color compression processing actually performed, in addition to the above effect, the lightness component after color compression Can be corrected with high accuracy.

  (4) In the image processing apparatus according to another aspect of the present invention, the compression rate calculation unit includes a saturation correction curve indicating a relationship between a saturation component Cin before color compression and a saturation component Cout after color compression. As the compression rate of the saturation component, the reciprocal number ΔCin / ΔCout of the gradient in the saturation component Cin is calculated.

  According to this aspect, since the compression rate in the color compression processing performed according to the saturation correction curve can be faithfully reflected in the color compression processing actually performed, in addition to the above effect, the color after color compression can be reflected. The degree component can be corrected with high accuracy.

  (5) An image processing apparatus according to another aspect of the present invention includes a lightness noise removal unit that removes a given lightness noise component from the lightness component, and the lightness component correction unit calculates a correction amount of the lightness component. And correcting the lightness component of the image data from which the lightness noise component has been removed by the lightness noise removing unit.

  According to this aspect, since the lightness component from which lightness noise has been removed is corrected using the correction amount, in addition to the above effects, the correction of the image signal for distinguishing between detail and lightness noise is enhanced. It will be possible to do with accuracy.

  (6) In the image processing device according to another aspect of the present invention, the lightness component correction amount calculation unit increases the lightness component amplification amount as the lightness noise component amount removed by the lightness noise removal unit decreases. The correction amount of the brightness component is calculated so as to increase.

  According to this aspect, in addition to the above-described effect, it is possible to avoid the situation where the brightness noise is amplified and to surely improve the appearance of the detail portion of the image by color compression.

  (7) In the image processing apparatus according to another aspect of the present invention, assuming that the lightness component before color compression is Lin and the lightness component Lout after color compression, the lightness component correction amount calculation unit calculates the lightness compression rate. The correction amount of the lightness component is calculated so that the amplification amount of the lightness component increases as the value increases.

  According to this aspect, in addition to the above effect, it is possible to reliably improve the appearance of the detail portion of the image lost due to the color compression.

  (8) In the image processing apparatus according to another aspect of the present invention, the lightness component correction amount calculation unit is configured to increase the amplification amount of the lightness component in the high frequency region from the low frequency region in the spatial frequency band. The correction amount of the brightness component is calculated.

  According to this aspect, in addition to the above effect, it is possible to reliably improve the appearance of the detail portion of the image lost by color compression without amplifying the brightness noise.

  (9) An image processing apparatus according to another aspect of the present invention includes a saturation noise removing unit that removes a given saturation noise component from the saturation component, and the saturation component correction unit includes the saturation component. Using the correction amount of the component, the saturation component of the image data from which the saturation noise component has been removed by the saturation noise removal unit is corrected.

  According to this aspect, since the saturation component from which the saturation noise has been removed is corrected using the correction amount, in addition to the above effect, the image signal for distinguishing between the detail and the saturation noise can be obtained. Correction can be performed with high accuracy.

  (10) In the image processing device according to another aspect of the present invention, the saturation component correction amount calculation unit decreases the amount of the saturation noise component that is removed by the saturation noise removal unit. The correction amount of the saturation component is calculated so that the amplification amount of the component becomes large.

  According to this aspect, in addition to the above effect, it is possible to avoid a situation where the saturation noise is amplified and to surely improve the appearance of the detail portion of the image by color compression.

  (11) In the image processing apparatus according to another aspect of the present invention, assuming that the saturation component before color compression is Cin and the saturation component Cout after color compression, the saturation component correction amount calculating unit The amount of correction of the saturation component is calculated so that the amount of amplification of the saturation component increases as the compression ratio increases.

  According to this aspect, in addition to the above effect, it is possible to reliably improve the appearance of the detail portion of the image lost due to the color compression.

  (12) In the image processing device according to another aspect of the present invention, the saturation component correction amount calculation unit may increase the amplification amount of the saturation component in the high-frequency region in the spatial frequency band than in the low-frequency region. Then, the correction amount of the saturation component is calculated.

  According to this aspect, in addition to the above-described effect, it is possible to reliably improve the appearance of the detail portion of the image lost by color compression without amplifying the saturation noise.

  (13) In another aspect of the present invention, an image output device that outputs an image based on image data is an image based on any of the image processing devices described above and the image data corrected by the image processing device. And an image output unit for outputting.

  According to this aspect, it is possible to provide an image output apparatus to which an image processing apparatus that improves the appearance of image details when color compression is performed.

  (14) According to another aspect of the present invention, there is provided an image processing method for correcting image data supplied to an image output device based on a color gamut of an input image and a color gamut of the image output device. The lightness component of the image data is compressed at a compression rate of the lightness component of the image data corresponding to the hue component of the data, and the saturation of the image data is compressed at the compression rate of the saturation component of the image data corresponding to the hue component. A color compression step for compressing a brightness component, and a brightness component correction amount calculation for calculating a brightness component correction amount of the image data in accordance with a compression ratio of the brightness component for image data in a given spatial frequency band A saturation component correction amount calculating step for calculating a saturation component correction amount of the image data in accordance with a compression ratio of the saturation component for image data in a given spatial frequency band; and Lightness component correction Using the lightness component correction step for correcting the lightness component of the image data compressed in the color compression step, and using the correction amount of the saturation component, the image data compressed in the color compression step And a saturation component correction step for correcting the saturation component.

  In this aspect, based on the color gamut of the input image and the color gamut of the image output device, the lightness component and the saturation component of the image data are compressed at a compression rate corresponding to the hue component of the image data. At this time, for the image data in a given spatial frequency band, the brightness component of the image data is corrected in accordance with the compression ratio at the time of the above compression processing, so that it was lost due to the compression of the brightness component. By correcting the portion, it is possible to improve the appearance of the detail portion of the image that is lost on the high lightness side during color compression. Similarly, with respect to image data in a given spatial frequency band, the saturation component of the image data is corrected according to the compression ratio at the time of the above compression processing, so the compression of the saturation component is performed. By correcting the lost portion, the appearance of the detail portion of the image lost on the high saturation side during color compression can be improved.

  (15) An image processing method according to another aspect of the present invention is based on the color gamut of the input image and the color gamut of the image output device, and the compression ratio and the color of the lightness component according to the hue component. A compression rate calculation step of calculating a compression rate of the brightness component, wherein the color compression step compresses the brightness component of the image data with the compression rate of the brightness component calculated in the compression rate calculation step, and The saturation component of the image data is compressed with the compression rate of the saturation component calculated in the compression rate calculation step.

  According to this aspect, since the compression rate is calculated based on the color gamut of the input image and the color gamut of the image output device, in addition to the above effects, the lightness component and the saturation of the input image data Optimum correction can be performed on the components, and it is possible to contribute to high image quality of the image after color compression.

  (16) In another aspect of the present invention, a program causes a computer to execute any one of the image processing methods described above.

  According to this aspect, it is possible to improve the appearance of image details and to provide a computer-executable program.

1 is a block diagram of a configuration example of an image display system according to an embodiment of the present invention. Explanatory drawing of the correction process performed in the image process part of FIG. The block diagram of the hardware structural example of the image process part of FIG. Operation | movement explanatory drawing of the compression rate calculation circuit of FIG. FIG. 5A and FIG. 5B are explanatory diagrams of a lightness correction curve and a saturation correction curve that are referred to during color compression processing. 6A and 6B are diagrams for explaining the operation of the color compression circuit. FIG. 4 is a block diagram of a configuration example of a detail emphasis circuit in FIG. 3. FIG. 8 is a block diagram of a configuration example of a noise extraction / removal circuit in FIG. 7. The figure which shows an example of the filter characteristic of the HPF circuit and LPF circuit in a detail emphasis circuit. The operation explanatory view of a weighting calculation circuit. Explanatory drawing of the weighting coefficient which the weighting calculation circuit demonstrated in FIG. 10 outputs. The block diagram of the structural example of the multistage filter circuit of FIG. The block diagram of the structural example of the lightness signal correction amount calculation circuit of FIG. FIG. 14 is an operation explanatory diagram of the weight calculation circuit of FIG. 13. FIG. 15 is an operation explanatory diagram of the brightness gain calculation circuit of FIG. 14. Explanatory drawing of the brightness gain calculated by the brightness gain calculation circuit. Explanatory drawing of the effect of the detail emphasis process of the image process part in this embodiment. The flowchart of the example of a process of the image process part in this embodiment. FIG. 19 is a flowchart of a processing example of detail enhancement processing of FIG. 18 of the image processing unit in the present embodiment. FIG. 19 is a flowchart of a processing example of detail enhancement processing of FIG. 18 of the image processing unit in the present embodiment. The figure of the structural example of the projection part of FIG. 1 or FIG. The block diagram of the structural example of the lightness signal correction amount calculation circuit in the 1st modification of this embodiment. 23A, FIG. 23B, and FIG. 23C are explanatory diagrams of operations of the first to third LUTs of FIG. The block diagram of the structural example of the lightness signal correction amount calculation circuit in the 2nd modification of this embodiment. FIG. 25 is an operation explanatory diagram of the LUT in FIG. 24. The figure which shows an example of the filter characteristic of the HPF circuit in the detail emphasis circuit in the 3rd modification of this embodiment, and an LPF circuit. Explanatory drawing of the effect of the detail emphasis process of the image process part in the 3rd modification of this embodiment. FIG. 10 is a block diagram of a configuration example of a printer according to a fourth modification of the embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. In addition, all of the configurations described below are not necessarily indispensable configuration requirements for solving the problems of the present invention.

  In the following embodiments, an image display apparatus is described as an example of the image output apparatus according to the present invention. However, the image output apparatus according to the present invention is not limited to the image display apparatus. Similarly, an image display system will be described as an example of an image output system to which the image output apparatus according to the present invention is applied. However, the image output system to which the image output apparatus according to the present invention is applied is limited to the image display system. It is not a thing. Moreover, although the projector which is an image projection apparatus is demonstrated to an example as this image display apparatus, the image display apparatus which concerns on this invention is not limited to a projector.

1. Image Display System FIG. 1 is a block diagram showing a configuration example of an image display system according to an embodiment of the present invention.

  The image display system (image output system in a broad sense) 10 includes a projector (image output device in a broad sense) 20 that is an image display device, and a screen SCR. The projector 20 modulates light from a light source (not shown) based on the input image data, and displays the image by projecting the modulated light onto the screen SCR. Here, the color gamut of the input image represented by the input image data is partially wider than the color gamut of the projector 20 (projection unit 100), and the projector 20 performs color compression or color expansion on the input image data. The image is displayed based on the image data after color compression or color expansion.

  The projector 20 includes an image processing unit 30 (an image processing device in a broad sense) and a projection unit 100 (an image output unit in a broad sense). The image processing unit 30 is input so as to be able to express the details of the low brightness part and the high brightness part of the display image and the detail of the low saturation part and the high saturation part without affecting the brightness area and the saturation area that are not to be corrected. The image data is corrected, and the corrected image data is output to the projection unit 100. The projection unit 100 projects light modulated based on the image data from the image processing unit 30 onto the screen SCR. At this time, the image processing unit 30 selects the image according to the compression rate so that the detail is enhanced even when color compression or color expansion is performed based on the color gamut of the input image data and the color gamut of the projection unit 100. Correct the data.

  1 shows an example in which the image processing unit 30 is provided inside the projector 20, but the image processing unit 30 may be provided outside the projector 20 or inside the projection unit 100. Also good.

2. 2.1 Image Processing Unit 2.1 Overview of Processing In the present embodiment, the following correction processing is performed on each of the lightness component and the saturation component of image data, thereby changing the lightness change and saturation change of the detail portion of the input image. To improve the appearance of the image. In the following, since the color expansion process is different in the compression direction of the color compression process, it will be described as “color compression”. Therefore, “decompression ratio” is also one of “compression ratios”, and “compression ratio less than 1” has the same meaning as “decompression ratio”.

  FIG. 2 is an explanatory diagram of correction processing performed in the image processing unit 30 of FIG. FIG. 2 shows an outline of correction processing by color compression for the brightness component of the image data. In FIG. 2, as the image characteristics represented by each image data being corrected, the horizontal position of the image is schematically shown on the horizontal axis, and the brightness level is schematically shown on the vertical axis. In FIG. 2, illustration of lightness noise described later is omitted.

  The input image IMGin is, for example, an image having a low brightness on the left side and a high brightness on the right side, and has a minute change in the low brightness region and a minute change in the high brightness region. The color compression unit C1 performs color compression according to a lightness correction curve indicating the relationship between the lightness component of the input image IMGin before color compression and the lightness component after color compression, and generates an output image IMG1 after color compression. The color compression means C1 performs color compression according to a brightness correction curve as shown in FIG. As a result, in the output image IMG1, the information on the detail portion is lost on the high brightness side.

Therefore, in the present embodiment, processing for emphasizing a detail portion lost on the high brightness side is performed using the compression rate in the color compression processing performed by the color compression unit C1. Therefore, the signal extracting unit L1, of the luminance component of the image data of the output image IMG1 after color compression by color compression means C1, extracts a signal L _H lightness components in the predetermined spatial frequency band. In Figure 2, corresponding to the spatial frequency is set gain, the signal extracting unit L1 extracts a signal L _H lightness component of this gain is large spatial frequency band.

The lightness gain generation means G1 generates a gain g corresponding to the compression rate performed by the color compression means C1. The lightness gain generating means G1 generates the gain g so that it is smaller on the low lightness side and larger as it becomes lighter. For example, the lightness gain generation unit G1 generates a gain g corresponding to the slope of the lightness correction curve in the color compression processing performed by the color compression unit C1. The multiplier M1 multiplies the signal L _H and the gain g extracted by the signal extracting unit L1, generates the correction data D1 is a correction amount corresponding to the compression ratio. The correction data D1 is data in which the correction amount is small on the low lightness side and the correction amount is large on the high lightness side.

  The adder A1 adds the output image IMG1 (lightness component) after color compression by the color compression means C1 and the correction data D1, and outputs a lightness signal (lightness component) Lout constituting the corrected image data.

Although not shown, correction processing is also performed on the saturation component of the input image IMGin in FIG. 2 in the same manner as the lightness component. In this case, the saturation gain generator, corresponding to the inclination of the different saturation correction curve and brightness correction curve to generate a gain, multiplies the signal C _H and the gain that has been extracted by the signal extraction means. The correction data obtained in this way is data with a small correction amount on the low saturation side and a large correction amount on the high saturation side. Then, the output image (saturation component) after color compression and the correction data are added, and a saturation signal (saturation component) Cout constituting the corrected image data is output.

  In this way, image data in which the brightness component and the saturation component are corrected is output to the projection unit 100. Thereby, when color compression is performed, the appearance of the detail portion of the image can be improved.

2.2 Configuration example [Overall configuration]
FIG. 3 shows a block diagram of a hardware configuration example of the image processing unit 30 in FIG. FIG. 3 schematically shows the input image data and also shows the projection unit 100. In the following, in the input image data, the pixel value of each pixel is represented by the RGB color system, and each pixel is configured by R component, G component, and B component image data.

  The image processing unit 30 receives input image data 2 generated by an image generation device (not shown). The image processing unit 30 corrects the input image data 2 as described above, and outputs the corrected image data to the projection unit 100. At this time, the color gamut data of the input image of the input source and the color gamut data of the projection unit 100 that is the output destination are acquired, and color compression is performed based on both color gamut data, and the compression at the time of this color compression processing The image data is corrected according to the rate.

  Here, the function of the image generation apparatus is realized by, for example, a personal computer (PC). The input image data 2 includes image data 4 in which each pixel is composed of R component, G component, and B component image data, and color gamut data 6 corresponding to the image data 4. The color gamut data 6 is closed surface data on the CIELAB color space that contains the color gamut of the color space of the input image represented by the image data 4 or the color distribution in the input image. The color gamut data 6 has a known data format such as an ICC (International Color Consortium) profile or GamutID.

  The color gamut data 8 of the projection unit 100 is also provided in advance or inside the projection unit 100 so that the image processing unit 30 can acquire it by any means. The color gamut data 8 is also in the same data format as the color gamut data 6, and has a known data format such as an ICC profile or GamutID. When the data format of the color gamut data 8 is different from the data format of the color gamut data 6, the data format of both color gamut data is changed by a known data format conversion process inside or outside the image processing unit 30, for example. Match. Further, the color gamut data 8 may be generated based on measurement data of an image actually displayed by the projection unit 100.

The image processing unit 30 to which such color gamut data 6 and 8 are input includes an input image color gamut data storage unit 32, a display device color gamut data storage unit 34, a compression rate calculation circuit (compression rate calculation unit) 36, RGB → L ^* C ^* h ^* conversion circuit 40, color compression circuit (color compression unit) 50, line memory 60, L ^* C ^* h ^* → RGB conversion circuit 70, detail enhancement circuit (detail enhancement unit) 200L, 200C included .

  The input image color gamut data storage unit 32 stores the color gamut data 6 constituting the input image data 2 from the image generation apparatus. The display device color gamut data storage unit 34 stores the color gamut data 8 acquired by performing read control on the projection unit 100 and the like.

  The compression rate calculation circuit 36 is based on the color gamut data stored in the input image color gamut data storage unit 32 and the color gamut data stored in the display device color gamut data storage unit 34, and the colors in the color gamut of the input image. Is associated with a color within the color gamut of the projection unit 100. When the data format of the color gamut data stored in the input image color gamut data storage unit 32 is different from the data format of the color gamut data stored in the display device color gamut data storage unit 34, a compression rate calculation circuit. In 36, a conversion process for matching the data formats of both color gamut data is performed.

FIG. 4 is an operation explanatory diagram of the compression rate calculation circuit 36 of FIG. FIG. 4 shows the color gamut of the input image data and the color gamut of the projection unit 100 two-dimensionally, with the horizontal axis representing the chroma C ^* in the CIELAB color space and the vertical axis representing the lightness L ^* in the CIELAB color space. Is.

For example, when the color gamut of the input image data and the color gamut of the projection unit 100 are different, it is necessary to compress or expand the color to a color within the color gamut of the projection unit 100. More specifically, when the color within the color gamut of the input image data is a color outside the color gamut of the projection unit 100, the color needs to be compressed to a color within the color gamut of the projection unit 100, for example, as shown in FIG. Thus, the lightness component is compressed or expanded, and the saturation component is compressed. At this time, the compression rate calculation circuit 36 compresses or expands the coordinates (C ^* _{in_0} , L ^* _{in_0} ) of the color gamut of the input image data, for example, and coordinates (C ^{* A} brightness correction curve and a saturation correction curve are generated for each hue (hue component) so that ^* _{out_0} , L ^* _{out_0} ).

  FIG. 5A and FIG. 5B are explanatory diagrams of a lightness correction curve and a saturation correction curve that are referred to during color compression processing. FIG. 5A shows an example of a brightness correction curve, where the horizontal axis represents the brightness before color compression and the vertical axis represents the brightness after color compression. FIG. 5B shows an example of a saturation correction curve with the horizontal axis representing the saturation before color compression and the vertical axis representing the saturation after color compression. 5A and 5B, portions corresponding to those in FIG. 4 are denoted by the same reference numerals, and description thereof is omitted as appropriate.

As shown in FIG. _5A , _assuming that the lightness of the target pixel before color compression is L ^* _in and the lightness of the target pixel after color compression is L ^* _out , the compression rate calculation circuit 36 uses L ^* _{in_0} , for example. A lightness correction curve that changes linearly but changes in inclination is generated for each hue. According to this brightness correction curve, the colors in the color gamut of the input image are associated with the colors in the color gamut of the projection unit 100 on a one-to-one basis. The compression ratio calculating circuit 36 calculates the inverse of the slope in some ^L _{* in} the ^{_{(= ΔL * in / ΔL *}} out) as the compression ratio alpha _L.

Similarly, as shown in FIG. 5B, assuming that the saturation of the target pixel before color compression is C ^* _in and the saturation of the target pixel after color compression is C ^* _out , the compression rate calculation circuit 36 A linearly changing saturation correction curve is generated for each hue. According to this saturation correction curve, the colors in the color gamut of the input image are associated with the colors in the color gamut of the projection unit 100 on a one-to-one basis. The compression ratio calculating circuit 36 calculates the inverse of the slope in some ^C _{* in} the _{^{(= ΔC * in / ΔC *}} out) as the compression ratio alpha _C.

In FIG. 3, an RGB → L ^* C ^* h ^* conversion circuit 40 converts the pixel value of each pixel constituting the image data 4 from the RGB color system to the L ^* C ^* h ^* color system in the CIELAB color space. Each pixel value is converted into a lightness signal (lightness component) L ^* , a saturation signal (saturation component) C ^* , and a hue signal (hue component) h ^* in the L ^* C ^* h ^* color system. In the present embodiment, the data format of the pixel value of each pixel of the image data 4 is the RGB format, and processing is performed with the lightness signal L ^* , the saturation signal C ^* , and the hue signal h ^* in the image processing unit 30. However, the present embodiment is not limited to the data format of the image data 4 or the signal format in the image processing unit 30.

The hue signal h ^* converted by the RGB → L ^* C ^* h ^* conversion circuit 40 is supplied to the line memory 60. The line memory 60 receives the hue signal h ^* from the RGB → L ^* C ^* h ^* conversion circuit 40. save.

The lightness signal L ^* , the saturation signal C ^*, and the hue signal h ^* converted by the RGB → L ^* C ^* h ^* conversion circuit 40 are supplied to the color compression circuit 50. The color compression circuit 50 performs the lightness signal L ^{* on} the lightness signal L ^* according to the lightness correction curve corresponding to the hue signal h ^* (for example, see FIG. 5A) among the lightness correction curves generated by the compression rate calculation circuit 36. Perform color compression. Further, the color compression circuit 50 follows the saturation correction curve corresponding to the hue signal h ^* among the saturation correction curves generated by the compression rate calculation circuit 36 (see, for example, FIG. 5B). Perform color compression on C ^* .

6A and 6B are diagrams for explaining the operation of the color compression circuit 50. FIG. FIG. 6A shows an operation explanatory diagram of the color compression circuit 50 for performing color compression processing on the lightness signal L ^* . FIG. 6B illustrates an operation explanatory diagram of the color compression circuit 50 for performing color compression processing on the saturation signal C ^* .

The color compression circuit 50 stores the information calculated by the compression rate calculation circuit 36 in, for example, a look-up table (LUT) format. The color compression circuit 50 refers to the information stored in the LUT format and outputs a lightness signal after color compression based on the lightness signal L ^* from the RGB → L ^* C ^* h ^* conversion circuit 40. , RGB → L ^* C ^* h ^* Based on the saturation signal C ^* from the conversion circuit 40, a saturation signal after color compression is output. More specifically, the color compression circuit 50 includes an input value L ^* _in and an output value L ^* _{out at} a plurality of sampling points on the brightness correction curve calculated by the compression rate calculation circuit 36 for each hue signal h ^*. The compression rate α _{L at} each sampling point is stored in the LUT format. In addition, the color compression circuit 50 includes, for each hue signal h ^* , input values C ^* _in and output values C ^* _{out at} a plurality of sampling points on the saturation correction curve calculated by the compression rate calculation circuit 36, and each sampling. The compression rate α _{C at the} point is stored in the LUT format. When the brightness signal L ^* from the RGB → L ^* C ^* h ^* conversion circuit 40 is input, the color compression circuit 50 corresponds to the hue signal h ^* from the RGB → L ^* C ^* h ^* conversion circuit 40. The lightness signal L ^* to be input is set as an input value L ^* _in , and an output value L ^* _{out corresponding} thereto is output. When the saturation signal C ^* from the RGB → L ^* C ^* h ^* conversion circuit 40 is input, the color compression circuit 50 converts the hue signal h ^* from the RGB → L ^* C ^* h ^* conversion circuit 40 into the hue signal h ^* . The corresponding saturation signal C ^* is set as an input value C ^* _in , and an output value C ^* _out corresponding thereto is output.

Note that the color compression circuit 50 performs an interpolation operation by a known interpolation method using information on two sampling points stored in the LUT according to the input value L ^* _in to obtain an output value L ^* _out . Thereby, the color compression circuit 50 can output a lightness signal after color compression according to the lightness correction curve generated by the compression ratio calculation circuit 36 for the lightness signal L ^* other than the sampling point. The color compression circuit 50 realizes the function of the color compression unit C1 of FIG. Similarly, the color compression circuit 50 performs an interpolation operation by a known interpolation method using information on two sampling points stored in the LUT according to the input value C ^* _in to obtain an output value C ^* _out . Thereby, the color compression circuit 50 can output a saturation signal after color compression according to the saturation correction curve generated by the compression rate calculation circuit 36 for the saturation signal C ^* other than the sampling point.

When the output values L ^* _out and C ^* _out are obtained, the color compression circuit 50 also outputs the compression ratios α _L and α _C corresponding thereto. The line memory 60 receives the hue signal h ^* from the RGB → L ^* C ^* h ^* conversion circuit 40, the lightness signal after color compression, the saturation signal, and the compression ratios α _L and α _C from the color compression circuit 50. Associate and save. The color compression circuit 50 according to the input value L ^* _in, performs known interpolation operation by the interpolation method using the compression ratio in the two sampling points stored in LUT, corresponding to the input value L ^* _in The compression rate α _L is obtained. The color compression circuit 50 according to the input value C ^* _in, performs known interpolation operation by the interpolation method using the compression ratio in the two sampling points stored in LUT, corresponding to the input value C ^* _in The compression rate α _C is obtained.

  The detail emphasis circuit 200L performs detail emphasis processing on the color-compressed lightness signal stored in the line memory 60. This detail enhancement process amplifies the change of the detail part (detail) according to the compression rate only for the specific frequency component of the brightness signal after color compression, without affecting other parts, This is a process for improving the appearance of detail parts lost during color compression. In this detail emphasis process, noise is extracted and the detail portion is enhanced according to the extracted noise amount, thereby improving the appearance of the detail portion lost during color compression without amplifying the noise.

  The detail emphasis circuit 200C performs detail emphasis processing on the chroma signal after color compression stored in the line memory 60. This detail enhancement process amplifies the change in detail (detail) only for a specific frequency component of the chroma signal after color compression, and is lost during color compression without affecting other parts. This is a process to improve the appearance of the detail part. In this detail emphasis process, noise is extracted and the detail portion is enhanced according to the extracted noise amount, thereby improving the appearance of the detail portion lost during color compression without amplifying the noise.

The lightness signal that has been subjected to the detail enhancement process by the detail enhancement circuit 200L and the saturation signal that has been subjected to the detail enhancement process by the detail enhancement circuit 200C, together with the hue signal h ^* stored in the line memory 60 corresponding thereto, L ^* C ^* h ^* → Supplied to the RGB conversion circuit 70. The L ^* C ^* h ^* → RGB conversion circuit 70 converts each pixel into a RGB color system pixel value for the input lightness signal, saturation signal, and hue signal h ^* . The RGB color system pixel values converted by the L ^* C ^* h ^* → RGB conversion circuit 70 are output to the projection unit 100.

2.3 Detailed Configuration Example 2.3.1 Detail Emphasis Circuit Since the detail enhancement circuit 200L and the detail enhancement circuit 200C have the same configuration, the detail enhancement circuit 200L will be described below. In the description of the detail emphasis circuit 200L, the description of the detail emphasis circuit 200C is made by replacing the word “lightness” with “saturation”.

FIG. 7 shows a block diagram of a configuration example of the detail emphasizing circuit 200L in FIG. 7 also shows the line memory 60, the detail emphasis circuit 200C, and the L ^* C ^* h ^* → RGB conversion circuit 70 of FIG.

  The detail enhancement circuit 200L includes a noise extraction / removal circuit (lightness noise removal unit) 210L, a multistage filter circuit (signal extraction unit) 230L, a lightness signal correction amount calculation circuit (lightness component correction amount calculation unit) 250L, and a lightness signal correction circuit ( Brightness component correction unit) 270L.

  The noise extraction / removal circuit 210L analyzes the spatial frequency of the brightness signal stored in the line memory 60. More specifically, the noise extraction / removal circuit 210 </ b> L can extract a high-frequency component of the lightness signal and remove lightness noise from the lightness signal from the line memory 60. The output highL, which is the absolute value of the high-frequency component of the brightness signal extracted by the noise extraction / removal circuit 210L, is supplied to the brightness signal correction amount calculation circuit 250L as an analysis result of the noise extraction / removal circuit 210L. The brightness signal from which the brightness noise has been removed by the noise extraction / removal circuit 210L is supplied to the brightness signal correction circuit 270L as the brightness signal NR.

  The multistage filter circuit 230L extracts a signal in a given spatial frequency band from the lightness signal (lightness signal after color compression) stored in the line memory 60. This multi-stage filter circuit 230L realizes the function of the signal extraction means L1 in FIG.

The lightness signal correction amount calculation circuit 250L corresponds to the lightness signal correction amount based on the output of the multistage filter circuit 230L, the compression rate stored in the line memory 60, and the analysis result of the noise extraction / removal circuit 210L. Correction data VA to be calculated is calculated. That is, the brightness signal correction amount calculating circuit 250L is outputted HighL (noise extraction and removal circuit 210L of analysis results) and in accordance with the compression ratio alpha _L, the multi-stage filter circuit given spatial frequency band of the luminance signal extracted by 230L The amount of correction for can be calculated. The lightness signal correction amount calculation circuit 250L can realize the function of the lightness gain generation means G1 in FIG.

  The lightness signal correction circuit 270L corrects the lightness signal NR from which lightness noise has been removed by the noise extraction / removal circuit 210L using the correction data calculated by the lightness signal correction amount calculation circuit 250L, and the lightness after detail enhancement processing. Output as a signal.

  Similarly, the detail enhancement circuit 200C includes a noise extraction / removal circuit (saturation noise removal unit) 210C, a multistage filter circuit (signal extraction unit) 230C, and a saturation signal correction amount calculation circuit (saturation component correction amount calculation unit) 250C. , A saturation signal correction circuit (saturation component correction unit) 270C. The saturation signal correction amount calculation circuit 260C includes a saturation gain calculation circuit 260C. And each part which comprises the detail emphasis circuit 200C operate | moves similarly to each corresponding part of the detail emphasis circuit 200L.

The brightness signal that has been subjected to detail enhancement processing by the detail enhancement circuit 200L, the saturation signal that has been subjected to detail enhancement processing by the detail enhancement circuit 200C, and the line memory 60 corresponding to the brightness signal and the saturation signal. The hue signal h ^* stored in the above is supplied to the L ^* C ^* h ^* → RGB conversion circuit 70.

  Below, each part which comprises the detail emphasis circuit 200L is demonstrated in detail.

[Noise removal / extraction circuit]
FIG. 8 shows a block diagram of a configuration example of the noise extraction / removal circuit 210L of FIG. FIG. 8 shows the line memory 60 together. In FIG. 8, the same parts as those in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  The noise extraction / removal circuit 210L includes a high-frequency component extraction circuit (high-frequency component extraction unit) 212L and a lightness noise removal circuit (lightness noise removal unit) 220L. The high frequency component extraction circuit 212L extracts a given high frequency component including lightness noise from the lightness signal stored in the line memory 60, and outputs the absolute value as an output highL. The lightness noise removal circuit 220L generates a lightness signal NR from which lightness noise has been removed from the lightness signal stored in the line memory 60. At this time, the lightness noise removal circuit 220L generates the lightness signal NR using the high frequency component extracted by the high frequency component extraction circuit 212L.

The high frequency component extraction circuit 212L includes a high pass filter (High Pass Filter: hereinafter abbreviated as HPF) circuit 214L. The brightness signal is input from the line memory 60 to the HPF circuit 214L, and the absolute value of the high-frequency component of the brightness signal is output as highL and output to the brightness signal correction amount calculation circuit 250L and the brightness noise removal circuit 220L. Such an HPF circuit 214L outputs an output highL as an absolute value of a high-frequency component according to the following equation by a known HPF process.

Here, highL is the output of the HPF circuit 214L, L is the input lightness signal, (x, y) is the coordinates of the target pixel, a _HPF is the filter coefficient, and (u, v) is the relative coordinates centered on the target pixel. Taking the above range in the system, s represents the size of the filter. For example, s may be “3”, but may be other than “3”.

The lightness noise removal circuit 220L includes a low pass filter (hereinafter abbreviated as LPF) circuit 222L, a weight calculation circuit 224L, multipliers 226L and 227L, and an adder 228L. The LPF circuit 222L receives the brightness signal from the line memory 60 and passes the low frequency component of the brightness signal. Such an LPF circuit 222L outputs an output lowL according to the following equation by a known LPF process.

Here, lowL is the output of the LPF circuit 222L, C is the input brightness signal, (x, y) is the coordinates of the target pixel, a _LPF is the filter coefficient, and (u, v) is the relative coordinates centered on the target pixel. Taking the above range in the system, s represents the size of the filter. For example, s may be “5”, but may be other than “5”, and is preferably larger than the filter size of the HPF circuit 214L.

  Note that it is desirable that the filter characteristics of the HPF circuit 214L in FIG. 8 and the filter characteristics of the LPF circuit 222L have the following relationship. Further, it is desirable that the HPF circuit 214L and the LPF circuit 222L in the detail emphasis circuit 200L and the HPF circuit 214C and the LPF circuit 222C (not shown) in the detail emphasis circuit 200C have the following relationship.

  FIG. 9 shows an example of filter characteristics of the HPF circuit and the LPF circuit in the detail emphasizing circuits 200L and 200C. In FIG. 9, the horizontal axis represents the frequency of the brightness signal and the saturation signal, and the vertical axis represents the gain.

The output of the HPF circuit 214L is small in a region where the spatial frequency of the lightness signal is low, and is large in a region where the spatial frequency of the lightness signal is high (T1 in FIG. 9). The cutoff frequency of the HPF circuit 214L is ωL _HPF . On the other hand, the output of the LPF circuit 222L increases in a region where the spatial frequency of the lightness signal is low, and decreases in a region where the spatial frequency of the lightness signal is high (T2 in FIG. 9). The cut-off frequency of the LPF circuit 222L is ωL _LPF . Here, it is desirable that the cutoff frequency of the HPF circuit 214L is equal to the cutoff frequency of the LPF circuit 222L (ωL _HPF = ωL _LPF = ω _cut0 ). As a result, the brightness signal can be corrected without losing the information of the original brightness signal.

Similarly, the output of the HPF circuit (214C) of the detail emphasis circuit 200C is small in a region where the spatial frequency of the saturation signal is low, and is large in a region where the spatial frequency of the saturation signal is high (T3 in FIG. 9). The cutoff frequency of this HPF circuit is ωC _HPF . On the other hand, the output of the LPF circuit (222C) of the detail emphasis circuit 200C increases in a region where the spatial frequency of the saturation signal is low and decreases in a region where the spatial frequency of the saturation signal is high (T4 in FIG. 9). The cutoff frequency of this LPF circuit is ωC _LPF . Here, it is desirable that the cutoff frequency of the HPF circuit is equal to the cutoff frequency of the LPF circuit ( _{ωC HPF} = _{ωC LPF} = ω _cut0 ). As a result, the saturation signal can be corrected without losing information of the original saturation signal.

Furthermore, the cut-off frequency omega _CUT0 HPF circuit 214L and LPF circuit 222L in detail enhancement circuit 200L is preferably equal to the cut-off frequency omega _CUT0 HPF circuit 214C and LPF circuit 222C in the detail enhancement circuit 200C. In this way, in the subsequent processing, desired signal components can be extracted for each of the lightness signal and the saturation signal, and optimal detail enhancement can be performed.

  Returning to FIG. The weighting calculation circuit 224L calculates a weighting amount according to the output from the high frequency component extraction circuit 212L. The weighting calculation circuit 224L stores the weighting amount corresponding to the output highL of the HPF circuit 214L in the LUT format, reads a value corresponding to the output from the HPF circuit 214L, or a plurality of values corresponding to the output from the HPF circuit 214L. A value obtained by a known interpolation operation using the value can be output.

  FIG. 10 shows an operation explanatory diagram of the weighting calculation circuit 224L.

The weight calculation circuit 224L outputs a weighting coefficient K _LPF to the multiplier 226L and outputs a weighting coefficient K _HPF to the multiplier 227L according to the output of the HPF circuit 214L. More specifically, the weighting calculation circuit 224L stores weighting coefficients K _HPF and K _LPF corresponding to the output from the HPF circuit 214L in advance in the LUT format. That is, the weighting calculation circuit 224L has weighting coefficients (K _HPF a, K _LPF a), (K _HPF b, K _LPF b), (K _HPF c, K _LPF c), which correspond to the outputs of the HPF circuit 214L in advance. Are stored, and when the output highL of the HPF circuit 214L is input, the weighting coefficients K _HPF and K _LPF corresponding thereto are output.

FIG. 11 is an explanatory diagram of the weighting coefficients K _HPF and K _LPF output from the weight calculation circuit 224L described in FIG. In FIG. 11, the horizontal axis represents the output of the HPF circuit 214L, and the vertical axis represents the weighting coefficients K _HPF and K _LPF as the weighting amounts output from the weight calculation circuit 224L.

The weighting calculation circuit 224L stores a weighting coefficient K _HPF that increases as the output highL of the HPF circuit 214L increases (T10 in FIG. 11) and decreases as the output highL of the HPF circuit 214L increases. The weighting coefficient K _LPF is stored (T11 in FIG. 11). In FIG. 11, the weighting coefficient _K HPF according to the output highL HPF circuit _214L, although _{K LPF} is increased or decreased linearly weighting factor _{K HPF, K LPF} is increased or decreased in accordance with a given function It may be.

In FIG. 8, the multiplier 226L outputs the multiplication result of the output of the LPF circuit 222L and the weighting coefficient K _LPF from the weight calculation circuit 224L, and outputs the result to the adder 228L. The multiplier 227L outputs the multiplication result of the output of the HPF circuit 214L and the weighting coefficient K _HPF from the weight calculation circuit 224L, and outputs the result to the adder 228L. The adder 228L adds the multiplication result of the multiplier 226L and the multiplication result of the multiplier 227L, and outputs the result as a lightness signal NR after removing lightness noise. That is, when the output of the HPF circuit 214L is highL and the output of the LPF circuit 222L is lowL, the lightness noise removal circuit 220L outputs the lightness signal NR according to the following equation.

As described above, since the weighting calculation circuit 224L outputs the weighting coefficients K _HPF and K _LPF as shown in FIG. 11, the lightness signal NR is a signal from which high-frequency lightness noise has been removed. The region where the output highL of the HPF circuit 214L is small is a region where there are many low frequency components. Since a minute high-frequency component in such a region is likely to be noise, the weighting coefficient K _HPF is reduced to remove the noise. That is, by reducing the weighting coefficient K _HPF and increasing the weighting coefficient K _LPF , it is possible to obtain a desired brightness signal NR without enhancing brightness noise. On the other hand, the region where the output highL of the HPF circuit 214L is large is a region where there are many high-frequency components. Since the high-frequency component in such a region is likely to be original image data, the weighting coefficient K _HPF is increased. That is, the desired brightness signal NR can be obtained by increasing the weighting coefficient K _HPF and decreasing the weighting coefficient K _LPF .

  In FIG. 8, the noise extraction / removal circuit 210L has been described as having a configuration including the high-frequency component extraction circuit 212L and the brightness noise removal circuit 220L. However, the noise extraction / removal circuit 210L is a high-frequency component extraction circuit. The brightness signal stored in the line memory 60 may be output as it is to the brightness signal correction circuit 270L as the brightness signal NR.

[Multi-stage filter circuit]
FIG. 12 shows a block diagram of a configuration example of the multistage filter circuit 230L of FIG. FIG. 12 also shows the line memory 60. In FIG. 12, the same parts as those in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  The multistage filter circuit 230L includes a first filter circuit 232L, a second filter circuit 234L, and a third filter circuit 236L having different filter sizes. FIG. 12 illustrates an example in which the multistage filter circuit 230L performs filter processing with three types of filter circuits, but the present embodiment is not limited to the number of filter circuits. That is, the multi-stage filter circuit 230L includes a plurality of filter circuits having different frequency bands of signals to be extracted, and each filter circuit includes pixel values of pixels arranged in the horizontal and vertical directions of the image, a filter coefficient matrix, and the like. It is sufficient if the result of the convolution operation can be output.

The first filter circuit 232L can output the filtered result according to the following equation.

  In the above equation, the output of the first filter circuit 232L is FO1, the lightness signal of the coordinates (x, y) is L (x, y), the filter coefficients are a, (i, j) are relative to the target pixel. Take the range of the above equation in coordinates and let the filter size be s. Each filter circuit receives a lightness signal having the number of lines (the number of vertical scanning lines) corresponding to the filter size.

  Although the above expression shows the output of the first filter circuit 232L, the second filter circuit 234L and the third filter circuit 236L can output the same filter processing result except for the filter size. (Outputs FO2, FO3).

  In the present embodiment, the filter size of the first filter circuit 232L is “3”, the filter size of the second filter circuit 234L is “5”, and the filter size of the third filter circuit 236L is “7”. However, the present embodiment is not limited to the filter sizes of the filter circuits of the first filter circuit 232L, the second filter circuit 234L, and the third filter circuit 236L.

[Lightness signal correction amount calculation circuit]
FIG. 13 shows a block diagram of a configuration example of the lightness signal correction amount calculation circuit 250L of FIG. In FIG. 13, the same parts as those in FIG. FIG. 13 also shows the line memory 60, the multistage filter circuit 230L, and the noise extraction / removal circuit 210L.
FIG. 14 is a diagram for explaining the operation of the weight calculation circuit 252L in FIG.
FIG. 15 is an operation explanatory diagram of the lightness gain calculation circuit 260L of FIG.

Lightness signal correction amount calculating circuit 250L includes weighting calculating circuit 252L, the multiplier 254L ₁ ~254L _3, the adder 256L, multiplier 258L, the brightness gain calculating circuit 260L.

The output highL generated by the HPF circuit 214L of the high frequency component extraction circuit 212L of the noise extraction / removal circuit 210L is input to the weighting calculation circuit 252L. Then, as shown in FIG. 14, the weight calculation circuit 252L calculates the weighting coefficients g _{1 to} g ₃ according to the output highL from the HPF circuit 214L. Such weighting calculating circuit 252L is input to the output highL from HPF circuit 214L, it is realized by the LUT which outputs the weighting coefficients _g 1 to g _3. Therefore, the weighting calculation circuit 252L includes weighting coefficients (g ₁ a, g ₂ a, g ₃ a), (g ₁ b, g ₂ b, g ₃ b) corresponding to the output highL from the HPF circuit 214L in advance. (G ₁ c, g ₂ c, g ₃ c),... Are stored, and when an output highL is input from the HPF circuit 214L, a weighting coefficient corresponding to the output is output.

  For example, it is desirable that the weighting calculation circuit 252L outputs a weighting coefficient that increases as the amount of lightness noise component decreases with the output highL of the HPF circuit 214L. As a result, the lightness component correction amount calculation circuit 250L can increase the lightness component correction amount (amplification amount) as the lightness noise component amount removed by the noise extraction / removal circuit 210L decreases.

The adder 256L adds the multiplication results of the multipliers 254L _{1 to} 254L ₃ , and outputs the addition result to the multiplier 258L. The multiplier 258L further receives the brightness gain coefficient h calculated by the brightness gain calculation circuit 260L.

The lightness gain calculation circuit 260L receives the compression rate α _L stored in the line memory 60. Then, the brightness gain calculating circuit 260L as shown in FIG. 15, according to the compression ratio alpha _L from the line memory 60, and calculates the brightness gain h.

Such brightness gain calculating circuit 260L receives the compression ratio alpha _L from the line memory 60 is implemented by LUT to brightness gain h output. Therefore, brightness gains ha, hb, hc,... Corresponding to the compression rate α _L from the line memory 60 are stored in advance in the brightness gain calculation circuit 260L, and the compression rate α _L is input from the line memory 60. When this is done, the brightness gain corresponding to this is output.

  FIG. 16 is an explanatory diagram of the brightness gain h calculated by the brightness gain calculation circuit 260L.

Brightness gain h lightness gain calculating circuit 260L is calculated, the compression ratio alpha _L, it is desirable to be expressed by the following equation.

In a region where the compression rate α _L is larger than 1, it means that color compression is performed on the lightness signal, and in a region where the compression rate α _L is smaller than 1, it means that color expansion is performed on the lightness signal pair. . With this lightness gain h, the lightness component correction amount (amplification amount) can be increased as the compression rate α _L increases. As a result, even when the detail portion is crushed by color compression, the correction data VA increases accordingly, and the appearance of the detail can be improved. On the other hand, when the compression rate α _L <1, the brightness gain h is 0, so that the low brightness side can be maintained without increasing the correction amount on the low brightness side.

As for the compression rate α _C of the saturation signal, the saturation component correction amount (amplification amount) can be increased as the compression rate α _C increases by the saturation gain calculated in the same manner as the lightness gain. . That is, even when the detail portion is crushed by color compression, the correction data is increased accordingly, and the appearance of the detail can be improved.

  In FIG. 13, the multiplier 258L multiplies the addition result of the adder 256L by the brightness gain h from the brightness gain calculation circuit 260L, and outputs the multiplication result as correction data VA corresponding to the correction amount of the brightness signal. . The correction data VA is input to the lightness signal correction circuit 270L. The brightness signal correction circuit 270L adds the correction data VA to the brightness signal NR from which the brightness noise component has been removed by the noise extraction / removal circuit 210L, and outputs the corrected brightness signal.

As described above, the lightness signal correction amount calculation circuit 250L corresponds to the signal in a given spatial frequency band extracted by the multistage filter circuit 230L (signal extraction circuit in a broad sense) and the compression rate α _L in the color compression processing. Based on the lightness gain coefficient calculated by the lightness gain calculation circuit 260L, the lightness signal correction amount can be calculated.

Each part constituting the detail enhancement circuit 200C is also the same as that shown in FIG. 8 to FIG. 16, the compression ratio alpha _L in the compression ratio alpha _C, it is possible to replace the output highL HPF circuit output highC like. Accordingly, the saturation signal correction amount calculation circuit corresponds to the signal in the given spatial frequency band extracted by the multistage filter circuit (signal extraction circuit in a broad sense) and the compression rate α _C in the color compression processing. Based on the saturation gain coefficient calculated by the gain calculation circuit, the correction amount of the saturation signal can be calculated.

  Note that the lightness signal correction amount calculation circuit 250L is not limited to the configuration shown in FIG. For example, in FIG. 13, the weight calculation circuit 252L may be input with FO1 to FO3 from the multistage filter circuit 230L.

  FIG. 17 shows an explanatory diagram of the effect of the detail enhancement processing of the image processing unit 30 in the present embodiment. In FIG. 17, the horizontal axis represents the output level of the HPF circuit 214L of the detail enhancement circuit 200L and the HPF circuit 214C of the detail enhancement circuit 200C, and the vertical axis represents the spatial frequency of the brightness signal and the saturation signal.

  In the present embodiment, as indicated by the lightness signal correction area LA1 and the saturation signal correction area CA1 in FIG. 17, the lightness and saturation are maintained as they are in the low-frequency areas of the lightness signal and the saturation signal. On the other hand, the appearance of the detail portion of the image is improved by performing correction over the high frequency region of the brightness signal and the saturation signal. At this time, it is determined that the higher the output level of the HPF circuit is in the high frequency regions of the lightness signal and the saturation signal, the more lightness noise and saturation noise are, and the output level of the HPF circuit is from the low level to the medium level. Correction is performed on a signal in a given level range Lar of the lightness component and a given level range Car of the saturation component.

  Therefore, as shown in FIG. 17, in the region where the output level of the HPF circuit is high, it is avoided to amplify the lightness noise and the saturation noise by avoiding the correction of the lightness signal and the saturation signal, while The lightness signal and the saturation signal are corrected from the medium level to the low level. Here, by correcting so that the correction amount (amplification amount) of the brightness signal and the saturation signal in the high frequency region is larger than that in the low frequency region, the appearance of the detail portion of the color-compressed image can be improved. it can.

  In the present embodiment, the lightness signal correction area LA1 is corrected on the higher frequency side than the saturation signal correction area CA1. As a result, it is possible to improve the appearance of an image in which details are crushed on the high brightness side rather than on the high saturation side. Further, the saturation signal correction area CA1 extends to an area where the output level of the HPF circuit is high compared to the lightness signal correction area LA1. As a result, the high frequency component of the saturation signal can be corrected as compared with the brightness signal, and the appearance of the detail portion of the image can be improved without amplifying the brightness noise.

  The processing of the image processing unit 30 having the above configuration can also be realized by software processing. In this case, the image processing unit 30 includes a central processing unit (hereinafter abbreviated as “CPU”), a read only memory (hereinafter abbreviated as “ROM”), or a random access memory (hereinafter “Random Access Memory”). CPU, which reads a program stored in ROM or RAM, controls hardware such as a multiplier and an adder by executing processing corresponding to the program, and Perform correction processing of the degree component.

  FIG. 18 shows a flowchart of a processing example of the image processing unit 30 in the present embodiment. When the processing in FIG. 18 is realized by software, a program for realizing the processing shown in FIG. 18 is stored in a ROM or RAM built in the image processing unit 30.

  First, the image processing unit 30 acquires the color gamut data of the input image and the color gamut data of the projection unit 100 as a color gamut data acquisition step (step S10). The color gamut data acquired in step S10 is stored in a RAM built in the image processing unit 30. At this time, the data format of both gamut data has a known data format such as an ICC profile or GamutID. If the data formats are different from each other, conversion processing is performed to match the data formats of both gamut data.

  Next, as described in FIGS. 5A and 5B, the image processing unit 30 performs the brightness correction curve and the saturation correction for each hue as the brightness correction curve generation step or the saturation correction curve generation step. A curve is generated (step S12). That is, the image processing unit 30 compresses or expands the lightness on the boundary of the color gamut of the input image data based on the color gamut data of the input image acquired in step S10 and the color gamut data of the projection unit 100. A brightness correction curve is generated so that the brightness is on the boundary of the color gamut of the projection unit 100. Further, the image processing unit 30 compresses and projects the saturation on the boundary of the color gamut of the input image data based on the color gamut data of the input image acquired in step S10 and the color gamut data of the projection unit 100. A saturation correction curve is generated so that the saturation is on the boundary of the color gamut of the unit 100.

Thereafter, as the compression rate calculation step, the image processing unit 30 calculates the compression rate α _L for each lightness correction curve generated in step S12 and the compression rate α _C for each saturation correction curve (step S14). This compression rate α _L corresponds to the reciprocal of the slope at several L ^* _in (= ΔL ^* _in / ΔL ^* _out ) _in each brightness correction curve. In addition, the compression rate α _C corresponds to the reciprocal of the slope at several C ^* _in (= ΔC ^* _in / ΔC ^* _out ) _in each saturation correction curve.

Subsequently, the image processing unit 30 starts accepting input image data corresponding to the input image as an input image data accepting step (step S16). Here, it is assumed that the pixel value of each pixel is expressed in the RGB color system. When the input image data is received in step S16, the image processing unit 30 converts the pixel value of each pixel of the input image data represented by the RGB color system into the L ^* C ^* h ^* color system, and the brightness signal. L ^* , saturation signal C ^* and hue signal h ^* are calculated (step S18).

Then, as the color compression step, the image processing unit 30 performs the lightness signal converted in step S18 according to the lightness correction curve corresponding to the hue signal h ^* converted in step S18 among the lightness correction curves generated in step S12. Color compression processing is performed on L ^* . Furthermore, the image processing unit 30 converts the saturation signal C ^* converted in step S18 to the saturation signal C ^* converted in step S18 according to the saturation correction curve corresponding to the hue signal h ^* converted in step S18 among the saturation correction curves generated in step S12. Then, color compression processing is performed (step S20). As a result, a lightness signal obtained by performing color compression processing (color expansion processing) on the lightness signal L ^* converted in step S18 and a compression rate corresponding to the inclination on the lightness correction curve used in the color compression processing are acquired. The Further, a saturation signal obtained by performing color compression processing on the saturation signal ^* converted in step S18 and a compression rate corresponding to the inclination on the saturation correction curve used in this color compression processing are acquired.

  As the detail enhancement processing step, the image processing unit 30 corresponds to the brightness signal after the color compression processing obtained as a result of the color compression processing in step S20 and the inclination on the brightness correction curve used in this color compression processing. The detail enhancement processing of the brightness signal is performed using the compression rate. Further, the image processing unit 30 performs, as the detail enhancement processing step, simultaneously with or subsequent to the detail enhancement processing of the lightness signal, and the saturation signal after the color compression processing obtained as a result of the color compression processing in step S20. Using the compression rate corresponding to the slope on the saturation correction curve used in the color compression processing, the saturation signal detail enhancement processing is performed (step S22).

Thereafter, the image processing unit 30 converts the brightness signal and the saturation signal after the detail enhancement processing into the RGB color system together with the hue signal h ^* corresponding to the brightness signal and the saturation signal (step S24), and the projection. The RGB color system pixel values are output to the unit 100 (step S26).

  Here, when the process ends (step S28: Y), the image processing unit 30 ends the series of processes (end). When the process does not end (step S28: N), the process returns to step S16 and continues the process. .

  FIG. 19 shows a flowchart of a processing example of the detail enhancement processing of FIG. 18 of the image processing unit 30 in the present embodiment. The process shown in FIG. 19 is performed as a detail enhancement process for the brightness component in step S22 of FIG. When the processing in FIG. 19 is realized by software, a program for realizing the processing shown in FIG. 19 is stored in a ROM or RAM built in the image processing unit 30.

  When the detail enhancement process is performed in step S22, the image processing unit 30 first extracts a specific spatial frequency band of the brightness signal as a signal extraction step (step S40). For example, when a light signal of a given spatial frequency band is extracted by the multi-stage filter circuit 230L, or is realized by software processing, the CPU controls a multiplier or an adder that realizes the function of the multi-stage filter circuit 230L. Then, the brightness signal in the above spatial frequency band is extracted.

  Thereafter, the image processing unit 30 analyzes the spatial frequency of the brightness signal (steps S42 and S44). More specifically, in step S42, the image processing unit 30 extracts a lightness signal of a given high-frequency component from the lightness signal after color compression as a high-frequency component extraction step. In step S44, the image processing unit 30 removes a lightness noise component from the lightness signal after color compression as a lightness noise removal step.

Then, the image processing unit 30, a lightness gain calculating step, calculating the brightness gain corresponding to the compression ratio alpha _L calculated in step S14 in FIG. 18 (step S46). Next, the image processing unit 30 calculates correction data corresponding to the correction amount of the lightness signal using the lightness gain calculated in step S46 as a lightness component correction amount calculation step (step S48). That is, in step S48, the image processing unit 30 weights the signal in the given spatial frequency band with a coefficient corresponding to the high-frequency component lightness signal (output highL of the HPF circuit 214L) extracted in step S42. The correction data VA is generated by multiplying the brightness gain calculated in step S46. Alternatively, when realized by software processing, the CPU weights the signal extracted by the signal extraction processing with a coefficient corresponding to the brightness signal of the high frequency component extracted in step S42, and then calculated in step S46. The brightness gain is multiplied and output as correction data VA.

  Then, the image processing unit 30 corrects the brightness signal from which the brightness noise has been removed in Step S44, using the correction data VA corresponding to the correction amount calculated in Step S48 as the brightness component correction step (Step S50). Then, the lightness signal after correction is output (step S52), and a series of processing ends (end). That is, in step S50, the lightness signal correction circuit 270L adds a correction signal corresponding to the correction data VA to the lightness signal after the color compression process, and generates a corrected lightness signal. Alternatively, when realized by software processing, the CPU adds a correction signal corresponding to the correction data VA to the lightness signal after the color compression processing to generate a lightness signal after correction.

  FIG. 20 shows a flowchart of a processing example of the detail enhancement processing of FIG. 18 of the image processing unit 30 in the present embodiment. The process shown in FIG. 20 is performed as the detail enhancement process of the saturation component in step S22 of FIG. When the processing in FIG. 20 is realized by software, a program for realizing the processing shown in FIG. 20 is stored in a ROM or RAM built in the image processing unit 30.

  When the detail enhancement process is performed in step S22, the image processing unit 30 first extracts a specific spatial frequency band of the saturation signal as a signal extraction step (step S60). For example, when a saturation signal of a given spatial frequency band is extracted by a multistage filter circuit or realized by software processing, the CPU controls a multiplier or an adder that realizes the function of the multistage filter circuit. The saturation signal in the spatial frequency band is extracted.

  Thereafter, the image processing unit 30 analyzes the spatial frequency of the saturation signal (steps S62 and S64). More specifically, in step S62, the image processing unit 30 extracts a saturation signal of a given high-frequency component from the saturation signal after color compression as a high-frequency component extraction step. In step S64, the image processing unit 30 removes a saturation noise component from the saturation signal after color compression as a saturation noise removal step.

Then, as the saturation gain calculation step, the image processing unit 30 calculates a saturation gain corresponding to the compression rate α _C calculated in step S14 of FIG. 18 (step S66). Next, the image processing unit 30 calculates correction data corresponding to the correction amount of the saturation signal using the saturation gain calculated in step S66 as the saturation component correction amount calculation step (step S68). That is, in step S68, the image processing unit 30 weights the signal in a given spatial frequency band with a coefficient corresponding to the saturation signal (HPF circuit output highC) extracted in step S62. Correction data is generated by multiplying the saturation gain calculated in step S66. Alternatively, when realized by software processing, the CPU weights the signal extracted by the signal extraction processing with a coefficient corresponding to the saturation signal of the high frequency component extracted in step S62, and then calculates in step S66. The saturation gain is multiplied and output as correction data.

  Then, as the saturation component correction step, the image processing unit 30 corrects the saturation signal from which the saturation noise has been removed in Step S64, using the correction data corresponding to the correction amount calculated in Step S68 (Step S64). In step S70, the corrected saturation signal is output (step S72), and the series of processing ends (end). That is, in step S70, the saturation signal correction circuit of the detail enhancement circuit 200C adds the correction signal corresponding to the correction data to the saturation signal after the color compression process, and generates a corrected saturation signal. Alternatively, when realized by software processing, the CPU generates a corrected saturation signal by adding a correction signal corresponding to the correction data to the saturation signal after the color compression processing.

  In the processing shown in FIG. 18, FIG. 19, or FIG. 20, the same processing can be realized even if the order of each step is appropriately changed.

  The RGB color system image data in which the pixel value of each pixel is corrected in this way is output to the projection unit 100. The projection unit 100 modulates the light from the light source based on the image data from the image processing unit 30, and projects the modulated light onto the screen SCR.

3. Projection Unit FIG. 21 shows a configuration example of the projection unit 100 of FIG. 1 or FIG. In FIG. 21, the projection unit 100 according to the present embodiment is described as being configured by a so-called three-plate type liquid crystal projector, but the projection unit as the image output device according to the present invention is configured by a so-called three-plate type liquid crystal projector. It is not limited to the thing. That is, in the following description, it is assumed that one pixel is composed of an R component sub-pixel, a G component sub-pixel, and a B component sub-pixel, but the number of sub-pixels (color component number) constituting one pixel is described. It is not limited.

  The projection unit 100 includes a light source 110, integrator lenses 112 and 114, a polarization conversion element 116, a superimposing lens 118, an R dichroic mirror 120R, a G dichroic mirror 120G, a reflection mirror 122, an R field lens 124R, and a G field lens 124G. , R liquid crystal panel 130R (first light modulation element), G liquid crystal panel 130G (second light modulation element), B liquid crystal panel 130B (third light modulation element), relay optical system 140, cross dichroic A prism 160 and a projection lens 170 are included. The liquid crystal panels used as the R liquid crystal panel 130R, the G liquid crystal panel 130G, and the B liquid crystal panel 130B are transmissive liquid crystal display devices. The relay optical system 140 includes relay lenses 142, 144, and 146 and reflection mirrors 148 and 150.

  The light source 110 is composed of, for example, an ultra-high pressure mercury lamp, and emits light including at least R component light, G component light, and B component light. The integrator lens 112 has a plurality of small lenses for dividing the light from the light source 110 into a plurality of partial lights. The integrator lens 114 has a plurality of small lenses corresponding to the plurality of small lenses of the integrator lens 112. The superimposing lens 118 superimposes the partial light emitted from the plurality of small lenses of the integrator lens 112 on the liquid crystal panel.

  The polarization conversion element 116 has a polarization beam splitter array and a λ / 2 plate, and converts light from the light source 110 into substantially one type of polarized light. The polarization beam splitter array has a structure in which a polarization separation film that separates the partial light divided by the integrator lens 112 into p-polarization and s-polarization, and a reflection film that changes the direction of the light from the polarization separation film are alternately arranged. Have. The polarization direction of the two types of polarized light separated by the polarization separation film is aligned by the λ / 2 plate. Light that has been converted into substantially one type of polarized light by the polarization conversion element 116 is applied to the superimposing lens 118.

  The light from the superimposing lens 118 enters the R dichroic mirror 120R. The R dichroic mirror 120R has a function of reflecting R component light and transmitting G component and B component light. The light transmitted through the R dichroic mirror 120R is applied to the G dichroic mirror 120G, and the light reflected by the R dichroic mirror 120R is reflected by the reflection mirror 122 and guided to the R field lens 124R.

  The dichroic mirror for G 120G has a function of reflecting G component light and transmitting B component light. The light transmitted through the G dichroic mirror 120G enters the relay optical system 140, and the light reflected by the G dichroic mirror 120G is guided to the G field lens 124G.

  In the relay optical system 140, in order to minimize the difference between the optical path length of the B component light transmitted through the G dichroic mirror 120G and the optical path length of the other R component and G component light, the relay lenses 142, 144, 146 is used to correct the difference in optical path length. The light transmitted through the relay lens 142 is guided to the relay lens 144 by the reflection mirror 148. The light transmitted through the relay lens 144 is guided to the relay lens 146 by the reflection mirror 150. The light transmitted through the relay lens 146 is applied to the B liquid crystal panel 130B.

  The light applied to the R field lens 124R is converted into parallel light and is incident on the R liquid crystal panel 130R. The R liquid crystal panel 130R functions as a light modulation element (light modulation unit), and the transmittance (passage rate, modulation rate) changes based on the R image signal. Therefore, the light (first color component light) incident on the R liquid crystal panel 130R is modulated based on the R image signal, and the modulated light is incident on the cross dichroic prism 160.

  The light applied to the G field lens 124G is converted into parallel light and is incident on the G liquid crystal panel 130G. The G liquid crystal panel 130G functions as a light modulation element (light modulation unit), and the transmittance (passage rate, modulation rate) changes based on the G image signal. Therefore, the light (second color component light) incident on the G liquid crystal panel 130G is modulated based on the G image signal, and the modulated light is incident on the cross dichroic prism 160.

  The B liquid crystal panel 130B irradiated with the light converted into parallel light by the relay lenses 142, 144, and 146 functions as a light modulation element (light modulation unit), and has a transmittance (passage rate) based on the B image signal. , Modulation rate) is changed. Therefore, the light (third color component light) incident on the B liquid crystal panel 130B is modulated based on the B image signal, and the modulated light is incident on the cross dichroic prism 160.

  The R liquid crystal panel 130R, the G liquid crystal panel 130G, and the B liquid crystal panel 130B have the same configuration. Each liquid crystal panel is a liquid crystal, which is an electro-optic material, sealed and encapsulated in a pair of transparent glass substrates. For example, a polysilicon thin film transistor is used as a switching element, and each color light passes corresponding to the image signal of each sub-pixel. Modulate rate.

  In this embodiment, a liquid crystal panel as a light modulation element is provided for each color component constituting one pixel, and the transmittance of each liquid crystal panel is controlled by an image signal corresponding to a sub pixel. That is, the image signal for the R component sub-pixel is used to control the transmittance (transmission rate, modulation factor) of the R liquid crystal panel 130R, and the image signal for the G component sub pixel is used for the G liquid crystal panel 130G. The B component sub-pixel image signal is used to control the transmittance of the B liquid crystal panel 130B.

  The cross dichroic prism 160 has a function of outputting combined light obtained by combining incident light from the R liquid crystal panel 130R, the G liquid crystal panel 130G, and the B liquid crystal panel 130B as outgoing light. The projection lens 170 is a lens that enlarges and forms an output image on the screen SCR.

  Since the image is displayed by the projection unit 100 having the above-described configuration based on the image data corrected by the image processing unit 30 in the present embodiment, even if color compression is performed, the image is lost due to color compression. The appearance of broken details can be improved. In addition, by amplifying the change in the detail part only for the specific frequency components of the brightness signal and the saturation signal after color compression, the detail part lost at the time of color compression without affecting other parts. The appearance can be improved. Further, by extracting the noise and emphasizing the detail portion according to the extracted noise amount, it is possible to improve the appearance of the detail portion lost during color compression without amplifying the noise.

  In addition, after performing the lightness signal and saturation signal correction processing in the present embodiment, the projection unit 100 is controlled as an image display step, and an image is displayed based on the image data after the correction processing. Thus, it is possible to provide an image display method that improves the expression of image details without affecting the brightness area and the saturation area that are not to be corrected.

4). Modified Example 4.1 First Modified Example In the image processing unit 30 according to the present embodiment, the lightness signal correction amount calculation circuit 250L and the saturation signal correction amount calculation circuit 250C, as shown in FIG. The correction data is generated by a multiplier that multiplies the weighting coefficient and the saturation gain coefficient. However, the present embodiment is not limited to this.

  Hereinafter, a modification of the lightness signal correction amount calculation circuit of the detail enhancement circuit 200L of FIG. 7 will be described. However, the saturation signal correction amount calculation circuit of the detail enhancement circuit 200C is the same, and at least one of the lightness signal correction amount calculation circuit of the detail enhancement circuit 200L and the saturation signal correction amount calculation circuit of the detail enhancement circuit 200C is changed to the following. Such a correction amount calculation circuit can be replaced.

  FIG. 22 is a block diagram showing a configuration example of the lightness signal correction amount calculation circuit 250La in the first modification of the present embodiment. For example, instead of the lightness signal correction amount calculation circuit 250L in the present embodiment, a lightness signal correction amount calculation circuit 250La shown in FIG. 22 is built in the detail emphasis circuit 200L in FIG.

The lightness signal correction amount calculation circuit 250La includes first to third LUTs 302L _{1 to} 302L ₃ , multipliers 304L _{1 to} 304L ₃ , and an adder 306L. The lightness signal correction amount calculation circuit 250La multiplies each output of the multistage filter circuit 230L by the lightness gain coefficient from each LUT of the _{first to third} LUTs 302L1 to 302L3, and then adds each multiplication result. Output as correction data VA.

FIG. 23A, FIG. 23B, and FIG. 23C show operation explanatory diagrams of the _first to third LUTs 302L _{1 to} 302L ₃ of FIG. Figure 23 (A) represents a view for explaining an operation of the first LUT302L ₁ in Figure 22. FIG. 23 (B) represents a second explanatory view of the operation of LUT302L ₂ in FIG. 22. FIG. 23C illustrates an operation explanatory diagram of the third LUT 302L ₃ in FIG.

The output L from the HPF circuit 214L and the compression rate α _L from the line memory 60 are input to the first LUT 302L ₁ , and the lightness gain coefficient j ₁ corresponding to the output high _L and the compression rate α _L is output. Therefore, brightness gain coefficients j ₁ a, j ₁ b, j ₁ c... Corresponding to the output high _L and the compression rate α _L are stored in the first LUT 302L ₁ in advance, and the output high _L and the compression rate α are stored. _L is adapted to output the brightness gain coefficient corresponding to the combination of the output highL and compression ratio alpha _L as lightness gain coefficient j ₁ when entered.

The output L from the HPF circuit 214L and the compression rate α _L from the line memory 60 are input to the second LUT 302L ₂ , and the lightness gain coefficient j ₁ corresponding to the output high _L and the compression rate α _L is output. Therefore, brightness gain coefficients j ₂ a, j ₂ b, j ₂ c... Corresponding to the output high _L and the compression rate α _L are stored in advance in the second LUT 302L ₂ , and the output high _L and the compression rate α are stored. _L is adapted to output the brightness gain coefficient corresponding to the combination of the output highL and compression ratio alpha _L as lightness gain coefficient j ₂ when entered.

The third LUT302L _3, the compression ratio alpha _L from the output highL and the line memory 60 from the HPF circuit 214L, and outputs the brightness gain coefficient _{j 1} corresponding to the output highL and compression ratio alpha _L. Therefore, brightness gain coefficients j ₃ a, j ₃ b, j ₃ c... Corresponding to the output high _L and the compression rate α _L are stored in advance in the third LUT 302L ₃ , and the output high _L and the compression rate α are stored. _L is adapted to output the brightness gain coefficient corresponding to the combination of the output highL and compression ratio alpha _L as lightness gain coefficient j ₃ when entered.

In Figure 22, the multiplier 304L ₁ multiplies the brightness gain coefficient _{j 1} from the first filter circuit LUT302L ₁ output FO1 a first of 232L constituting the multi-stage filter circuit 230L, the adder 306L multiplication result Output to. The multiplier 304L ₂ multiplies the brightness gain coefficient _{j 2} from the second filter circuit output of 234L FO2 and second LUT302L ₂ constituting the multi-stage filter circuit 230L, and outputs the multiplication result to the adder 306L. The multiplier 304L ₃ multiplies the brightness gain coefficient _{j 3} from the third filter circuit output FO3 the third LUT302L ₃ of 236L constituting the multi-stage filter circuit 230L, and outputs the multiplication result to the adder 306L.

The adder 306L adds the multiplication results of the multipliers 304L _{1 to} 304L ₃ and outputs the addition result as correction data VA.

As described above, in the image processing unit in the first modification of the present embodiment, the lightness signal correction amount calculation circuit 250La is provided for each output of the multistage filter circuit 230L, and the output highL and the compression rate α of the HPF circuit 214L. A plurality of tables for outputting a gain corresponding to _L , and a plurality of multiplications for multiplying each output of the multi-stage filter circuit 230L provided for each output of the multi-stage filter circuit 230L by the output of each table constituting the plurality of tables. And an adder for adding the multiplication results of a plurality of multipliers, and the output of the adder can be calculated as a correction amount for the brightness component. Further, the saturation signal correction calculation circuit can also calculate the correction amount of the saturation component in the same manner as described above.

According to the first modification of the present embodiment, as in the first embodiment, only the lightness signal in a given spatial frequency band can be corrected according to the compression rate α _L at the time of color compression. Similarly to the first embodiment, only the saturation signal in a given spatial frequency band can be corrected according to the compression rate α _C at the time of color compression. As a result, it is possible to improve the appearance of detail portions lost during color compression without affecting other portions. Furthermore, by extracting noise and emphasizing the detail portion according to the extracted noise amount, it is possible to improve the appearance of the detail portion lost during color compression without amplifying the noise. Furthermore, according to the first modification of the present embodiment, the number of multipliers incorporated in the lightness signal correction amount calculation circuit and the saturation signal correction amount calculation circuit can be reduced as compared with the first embodiment. Therefore, it is possible to reduce power consumption and cost.

4.2 Second Modification As shown in FIG. 22, the lightness signal correction amount calculation circuit 250La in the first modification of the present embodiment includes _first to third LUTs 302L _{1 to} 302L ₃ and a multiplier 304L. _{1 to} 304L ₃ and an adder 306L, and the multiplication results of the multipliers using the lightness gain coefficients from the _first to third LUTs 302L _{1 to} 302L ₃ are added. Is not limited to this.

  Hereinafter, a modification of the brightness signal correction amount calculation circuit built in the detail emphasis circuit 200L of FIG. 7 will be described. However, the saturation signal correction amount calculation circuit of the detail enhancement circuit 200C is the same, and at least one of the lightness signal correction amount calculation circuit of the detail enhancement circuit 200L and the saturation signal correction amount calculation circuit of the detail enhancement circuit 200C is changed to the following. Such a correction amount calculation circuit can be replaced.

  FIG. 24 is a block diagram showing a configuration example of the lightness signal correction amount calculation circuit 250Lb in the second modification example of the present embodiment. For example, instead of the lightness signal correction amount calculation circuit 250L in the present embodiment, a lightness signal correction amount calculation circuit 250Lb shown in FIG. 24 is built in the detail enhancement circuit 200L in FIG.

  The lightness signal correction amount calculation circuit 250Lb includes an LUT 352. The lightness signal correction amount calculation circuit 250Lb outputs the output from the LUT 352L as correction data VA.

  FIG. 25 is a diagram for explaining the operation of the LUT 352L in FIG.

The LUT 352L includes an output high _L from the HPF circuit 214L, a compression rate α _L from the line memory 60, and an output FO1 of each filter circuit of the first filter circuit 232L to the third filter circuit 236L constituting the multistage filter circuit 230L. ~FO3 are input, output HighL, and outputs the correction data corresponding to a combination of the output of the compression ratio alpha _L and each filter circuit. This correction data is output as correction data VA. Therefore, the LUT352L, previously HighL, the compression ratio alpha _L and the correction data VAa each corresponding to a combination of the output FO1~FO3 of each filter circuit, VAb, ···, VAc, VAd , ···, VAe, VAf, · · ·, Vaj · · · are stored, HighL, when the output of the compression ratio alpha _L and each filter circuit FO1~FO3 is input, and outputs a correction data corresponding to these combinations Yes.

As described above, in the image processing unit in the second modification of the present embodiment, the lightness signal correction amount calculating circuit 250Lb is corresponding to an output highL compression ratio of the output and HPF circuit 214L of the multi-stage filter circuit 230L alpha _L It is possible to include a table for outputting the correction data of the brightness component. Then, the correction data output by this table is output as correction data VA. Also, the saturation signal correction calculation circuit can output the saturation component correction amount in the same manner as described above.

According to the second modification of the present embodiment, as in the present embodiment or the first modification of the present embodiment, only a lightness signal in a given spatial frequency band is compressed with a compression rate α _L during color compression. It can be corrected according to. As a result, it is possible to improve the appearance of detail portions lost during color compression without affecting other portions. Also, only the saturation signal in a given spatial frequency band can be corrected according to the compression rate α _C at the time of color compression. As a result, it is possible to improve the appearance of detail portions lost during color compression without affecting other portions. Furthermore, by extracting noise and emphasizing the detail portion according to the extracted noise amount, it is possible to improve the appearance of the detail portion lost during color compression without amplifying the noise. Furthermore, according to the second modification of the present embodiment, the lightness signal correction amount calculation circuit and the saturation signal correction amount calculation circuit are incorporated in comparison with the first modification example of the first embodiment or the first embodiment. Therefore, the power consumption and the cost can be significantly reduced.

4.3 Third Modification In this embodiment or its modification, correction is made within the correction region shown in FIG. 17 with the gains of the HPF circuit and LPF circuit shown in FIG. It is not limited to this.

  In the third modification of the present embodiment, it is desirable that the filter characteristics of the HPF circuit 214L of the detail enhancement circuit 200L and the filter characteristics of the LPF circuit 222L have the following relationship. Similarly, it is desirable that the filter characteristics of the HPF circuit 214C of the detail emphasis circuit 200C and the filter characteristics of the LPF circuit 222C (not shown) have the following relationship. Further, it is desirable that the HPF circuit 214L and the LPF circuit 222L in the detail emphasis circuit 200L and the HPF circuit 214C and the LPF circuit 222C in the detail emphasis circuit 200C have the following relationship.

  FIG. 26 shows an example of filter characteristics of the HPF circuit and the LPF circuit in the detail emphasis circuits 200L and 200C in the third modification of the present embodiment. In FIG. 26, the horizontal axis represents the frequency of the brightness signal and the saturation signal, and the vertical axis represents the gain.

The output of the HPF circuit 214L is small in a region where the spatial frequency of the lightness signal is low, and is large in a region where the spatial frequency of the lightness signal is high (T21 in FIG. 26). The cutoff frequency of the HPF circuit 214L is ωL _HPF . On the other hand, the output of the LPF circuit 222L increases in a region where the spatial frequency of the brightness signal is low, and decreases in a region where the spatial frequency of the brightness signal is high (T22 in FIG. 26). The cut-off frequency of the LPF circuit 222L is ωL _LPF . Here, it is desirable that the cutoff frequency of the HPF circuit 214L is equal to the cutoff frequency of the LPF circuit 222L (ωL _HPF = ωL _LPF = ω _cut0 ).

Similarly, the output of the HPF circuit (214C) of the detail emphasizing circuit 200C is small in the region where the spatial frequency of the saturation signal is low, and is large in the region where the spatial frequency of the saturation signal is high (T23 in FIG. 26). The cutoff frequency of this HPF circuit is ωC _HPF . On the other hand, the output of the LPF circuit (222C) of the detail emphasis circuit 200C increases in a region where the spatial frequency of the saturation signal is low and decreases in a region where the spatial frequency of the saturation signal is high (T4 in FIG. 26). The cutoff frequency of this LPF circuit is ωC _LPF . Here, it is desirable that the cutoff frequency of the HPF circuit is equal to the cutoff frequency of the LPF circuit ( _{ωC HPF} = _{ωC LPF} = ω _cut1 ). As a result, the saturation signal can be corrected without losing information of the original saturation signal.

Further, the cutoff frequency ω _cut0 of the HPF circuit 214L and the LPF circuit 222L in the detail enhancement circuit 200L is lower than the cutoff frequency ω _cut1 of the HPF circuit 214C and the LPF circuit 222C in the detail enhancement circuit 200C. At this time, by making the lightness signal correction region and the saturation signal correction region have the following relationship, it is possible to improve the appearance of details of the lightness component that is more conspicuous than the saturation component.

  FIG. 27 is an explanatory diagram of the effect of the detail enhancement processing of the image processing unit in the third modification of the present embodiment. In FIG. 27, parts similar to those in FIG.

  The lightness signal correction area LA2 and the saturation signal correction area CA2 shown in FIG. 27 are different from the lightness signal correction area LA1 and the saturation signal correction area CA1 shown in FIG. 17 in that the lightness signal correction area LA2 and the saturation signal correction area CA2 are different. Is the point where the output level of the HPF circuit reaches the same region. Thus, as shown in FIG. 26, by removing more lightness noise components than the saturation noise components, the appearance of the detail portion of the image can be seen without much consideration of the correction regions of the lightness signal and the saturation signal. Will be able to improve.

4.4 Fourth Modification In this embodiment or its modification, a projector is described as an example of an image output apparatus. However, the present embodiment is not limited to this, and the image output apparatus is a printer. Also good.

  FIG. 28 shows a block diagram of a configuration example of a printer in the fourth modification example of the present embodiment. In FIG. 28, the same parts as those in FIG.

  The printer (image printing apparatus) 400 includes an image processing unit 30 and a printing unit 410 as an image output unit. The image processing unit 30 receives the color gamut data of the input image and the color gamut data of the printing unit 410. Then, the image processing unit 30 generates a lightness correction curve, a compression rate, a saturation correction curve, and a compression rate. When input image data is input, the image processing unit 30 performs color compression processing and prints the color-compressed image data. Output to the unit 410. The printing unit 410 performs printing based on the image data from the image processing unit 30.

  The image processing unit 30 in the fourth modified example of the present embodiment can be replaced with any one of the first to third modified examples of the present embodiment.

According to the fourth modification of the present embodiment, only the lightness signal in a given spatial frequency band can be corrected according to the compression rate α _L during color compression, as in the present embodiment or its modification. Also, only the saturation signal in a given spatial frequency band can be corrected according to the compression rate α _C at the time of color compression. As a result, it is possible to improve the appearance of detail portions lost during color compression without affecting other portions. Furthermore, by extracting noise and emphasizing the detail portion according to the extracted noise amount, it is possible to improve the appearance of the detail portion lost during color compression without amplifying the noise.

  As described above, the image processing apparatus, the image output apparatus, the image processing method, and the program according to the present invention have been described based on the above-described embodiment or its modification. However, the present invention is limited to the above-described embodiment or its modification. However, the present invention can be implemented in various modes without departing from the gist thereof, and for example, the following modifications are possible.

  (1) In each of the above-described embodiments or modifications thereof, an example in which color compression processing is performed in the CIELAB color space has been described, but the present invention is not limited to this. For example, the present invention can be applied to a case where color compression processing is performed in the CIELV color space or other color spaces.

  (2) In each of the above-described embodiments or modifications thereof, the example in which the image processing unit outputs the pixel value after converting it to the RGB color system has been described, but the present invention is not limited to this. The image processing unit may convert the color system to a color system other than the RGB color system (for example, CMYK color system) and output the result.

  (3) In each of the above-described embodiments or modifications thereof, the shape is not limited to the shape of the brightness correction curve and the saturation correction curve.

  (4) In each of the above-described embodiments or modifications thereof, the lightness noise and the saturation noise are removed by the noise extraction / removal circuit, and then the lightness signal saturation signal correction processing is performed. It is not limited. For example, a configuration in which the noise extraction / removal circuit 210L is omitted in FIG. 7 may be adopted, and the saturation signal correction process may be performed without removing the saturation noise.

  (5) In each of the above embodiments or modifications thereof, the projector has been described as an example of the image display device, but the present invention is not limited to this. The image display device according to the present invention can be applied to all devices that perform image display, such as a liquid crystal display device, a plasma display device, and an organic EL display device.

  (6) In each of the above-described embodiments or modifications thereof, it has been described that a light valve using a transmissive liquid crystal panel is used as the light modulation element. However, the present invention is not limited to this. For example, DLP (Digital Light Processing) (registered trademark), LCOS (Liquid Crystal On Silicon), or the like may be employed as the light modulation element.

  (7) In each of the above-described embodiments or modifications thereof, a light valve using a so-called three-plate transmissive liquid crystal panel as the light modulation element has been described as an example, but a single-plate liquid crystal panel, two plates, or four You may employ | adopt the light valve using the transmissive liquid crystal panel more than a plate type.

  (8) In each of the above embodiments, one pixel is described as being composed of three color component sub-pixels, but the present invention is not limited to this. The number of color components constituting one pixel may be 2, or 4 or more.

  (9) Although the present invention has been described as an image processing apparatus, an image output apparatus, an image processing method, and a program in each of the above-described embodiments or modifications thereof, the present invention is not limited to this. For example, an image display system including the image processing apparatus or the image output apparatus described above may be used. Alternatively, for example, a program describing a processing method of an image processing apparatus (image processing method) for realizing the present invention or a processing procedure of an image display apparatus processing method (image display method) for realizing the present invention Alternatively, it may be a recording medium on which the program is recorded.

2 ... Input image data, 4 ... Image data, 6, 8 ... Color gamut data,
DESCRIPTION OF SYMBOLS 10 ... Image display system, 20 ... Projector, 30 ... Image processing part,
32 ... Input image color gamut data storage unit, 34 ... Display device color gamut data storage unit,
36: Compression ratio calculation circuit, 40: RGB → L ^* C ^* h ^* conversion circuit, 50 ... Color compression circuit,
60 ... Line memory, 70 ... L ^* C ^* h ^* → RGB conversion circuit, 100 ... Projection unit,
110: Light source 112, 114: Integrator lens 116: Polarization conversion element
118 ... Superimposing lens, 120R ... R dichroic mirror,
120G ... Dichroic mirror for G, 122,148,150 ... Reflective mirror,
124R ... R field lens, 124G ... G field lens,
130R ... R liquid crystal panel, 130G ... G liquid crystal panel,
130B ... Liquid crystal panel for B, 140 ... Relay optical system,
142, 144, 146 ... relay lens, 160 ... cross dichroic prism,
170: Projection lens, 200C, 200L: Detail emphasis circuit,
210C, 210L ... noise extraction / removal circuit, 212L ... high frequency component extraction circuit,
214L ... HPF circuit, 220L ... lightness noise elimination circuit, 222L ... LPF circuit,
224L, 252L ... weight calculating _{circuit, 226L, 227L, 254L 1,} 254L 2, 254L 3, 258L, 304L 1, 304L 2, 304L 3, M1 ... multiplier,
228L, 256L, 306L, A1 ... adder,
230C, 230L ... multi-stage filter circuit, 232L ... first filter circuit,
234L ... second filter circuit, 236L ... third filter circuit,
250C, 250L, 250La, 250Lb ... saturation signal correction amount calculation circuit,
260C, 260L: Lightness gain calculation circuit, 270C, 270L: Lightness signal correction circuit,
302L ₁ ... 1st LUT, 302L ₂ ... 2nd LUT,
302L ₃ ... 3rd LUT, 352L ... LUT, 400 ... Printer,
410: printing section, C1: color compression means, L1: signal extraction means,
G1: Lightness gain generation means, SCR: Screen

Claims (16)

An image processing device for correcting image data supplied to an image output device,
Based on the color gamut of the input image and the color gamut of the image output device, the lightness component of the image data is compressed at the compression ratio of the lightness component of the image data corresponding to the hue component of the image data, and the hue A color compression unit that compresses the saturation component of the image data at a compression rate of the saturation component of the image data corresponding to the component;
A brightness component correction amount calculation unit that calculates a correction amount of a brightness component of the image data according to a compression rate of the brightness component, for image data in a given spatial frequency band;
A saturation component correction amount calculation unit that calculates a correction amount of a saturation component of the image data according to a compression rate of the saturation component for image data in a given spatial frequency band;
A brightness component correction unit that corrects the brightness component of the image data compressed by the color compression unit using the correction amount of the brightness component;
An image processing apparatus comprising: a saturation component correction unit that corrects a saturation component of the image data compressed by the color compression unit using the correction amount of the saturation component. In claim 1,
A compression rate calculation unit that calculates a compression rate of the lightness component and a compression rate of the saturation component according to the hue component based on the color gamut of the input image and the color gamut of the image output device;
The color compression unit is
The brightness component of the image data is compressed with the compression rate of the brightness component calculated by the compression rate calculation unit, and the compression rate of the saturation component calculated by the compression rate calculation unit is used to compress the image data. An image processing apparatus that compresses a saturation component. In claim 2,
The compression rate calculation unit
In a lightness correction curve showing a relationship between a lightness component Lin before color compression and a lightness component Lout after color compression, a reciprocal ΔLin / ΔLout of an inclination in the lightness component Lin is calculated as a compression rate of the lightness component Lin An image processing apparatus. In claim 2 or 3,
The compression rate calculation unit
In a saturation correction curve showing the relationship between the saturation component Cin before color compression and the saturation component Cout after color compression, the inverse of the slope ΔCin / ΔCout in the saturation component Cin is used as the compression rate of the saturation component. An image processing apparatus characterized by calculating. In any one of Claims 1 thru | or 4,
A brightness noise removing unit for removing a given brightness noise component from the brightness component;
The brightness component correction unit
An image processing apparatus, wherein the lightness component of the image data from which the lightness noise component has been removed by the lightness noise removal unit is corrected using the lightness component correction amount. In claim 5,
The lightness component correction amount calculation unit,
An image processing apparatus that calculates the correction amount of the lightness component such that the amount of amplification of the lightness component increases as the amount of the lightness noise component removed by the lightness noise removal unit decreases. In any one of Claims 1 thru | or 6.
The lightness component correction amount calculation unit,
An image processing apparatus that calculates the correction amount of the lightness component so that the amplification amount of the lightness component increases as the compression ratio of the lightness increases. In any one of Claims 1 thru | or 7,
The lightness component correction amount calculation unit,
An image processing apparatus that calculates a correction amount of the lightness component so that an amplification amount of the lightness component in a high frequency region is larger than a low frequency region in the spatial frequency band. In any one of Claims 1 thru | or 8.
A saturation noise removing unit that removes a given saturation noise component from the saturation component;
The saturation component correction unit is
An image processing apparatus that corrects a saturation component of the image data from which the saturation noise component has been removed by the saturation noise removal unit, using a correction amount of the saturation component. In claim 9,
The saturation component correction amount calculation unit,
Image processing for calculating the correction amount of the saturation component so that the amount of amplification of the saturation component increases as the amount of the saturation noise component removed by the saturation noise removal unit decreases apparatus. In any one of Claims 1 thru | or 10.
The saturation component correction amount calculation unit,
An image processing apparatus that calculates the correction amount of the saturation component such that the amplification amount of the saturation component increases as the compression rate of the saturation increases. In any one of Claims 1 thru | or 11,
The saturation component correction amount calculation unit,
An image processing apparatus that calculates a correction amount of the saturation component so that an amplification amount of the saturation component in a high frequency region is larger than that in a low frequency region in the spatial frequency band. An image output device that outputs an image based on image data,
An image processing apparatus according to any one of claims 1 to 12,
And an image output unit that outputs an image based on the image data corrected by the image processing device. An image processing method for correcting image data supplied to an image output device,
Based on the color gamut of the input image and the color gamut of the image output device, the lightness component of the image data is compressed at the compression ratio of the lightness component of the image data corresponding to the hue component of the image data, and the hue A color compression step of compressing the saturation component of the image data at a compression rate of the saturation component of the image data corresponding to the component;
A lightness component correction amount calculating step for calculating a lightness component correction amount of the image data in accordance with a compression rate of the lightness component for image data in a given spatial frequency band;
A saturation component correction amount calculating step for calculating a correction amount of a saturation component of the image data according to a compression rate of the saturation component for image data in a given spatial frequency band;
A lightness component correction step of correcting the lightness component of the image data compressed in the color compression step using the correction amount of the lightness component;
An image processing method comprising: a saturation component correction step of correcting a saturation component of the image data compressed in the color compression step using the correction amount of the saturation component. In claim 14,
A compression rate calculation step of calculating a compression rate of the lightness component and a compression rate of the saturation component according to the hue component based on the color gamut of the input image and the color gamut of the image output device;
The color compression step comprises:
The lightness component of the image data is compressed with the compression rate of the lightness component calculated in the compression rate calculation step, and the image data is compressed with the compression rate of the saturation component calculated in the compression rate calculation step. An image processing method comprising compressing a saturation component.   A program for causing a computer to execute the image processing method according to claim 14 or 15.