JP2011193332A - Projector and video projection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that, regarding a projector and a video projection method, a video image after trapezoidal distortion correction becomes darker than an original video image. <P>SOLUTION: A projector for projecting and displaying a video image on a projected surface includes: a distortion corrected video data generating unit for generating distortion corrected video data by applying, to original video data input to the projector, distortion correction processing for correcting distortion of a video image to be projected on the projected surface; a deformation rate deriving unit for deriving a deformation rate of a distortion corrected video image with respect to an original video image represented by the original video data for the distortion corrected video image represented by the distortion corrected video data; a luminance correcting unit for generating luminance corrected video data by correcting luminance of the distortion corrected video data on the basis of the deformation rate derived by the deformation rate deriving unit, the luminance correcting unit being configured to perform luminance correction so that as the deformation rate becomes smaller, luminance may be increased more by luminance correction; and a video light output unit for generating and outputting video light representing a video image on the basis of the luminance corrected video data. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a projector and an image projection method.

  When a rectangular image (hereinafter also referred to as an original image) is displayed on a projection surface such as a screen using a projector, the image displayed on the projection surface (hereinafter referred to as a projection image) depending on the relative positional relationship between the projector and the projection surface. (Also referred to as an image) may be distorted into a trapezoid, a parallelogram, or other quadrangle. Including the projection distortion other than the trapezoidal distortion, it is referred to as “trapezoidal distortion” in this specification. In this way, when trapezoidal distortion occurs in the projected image, a technique for correcting trapezoidal distortion that corrects the projected image to be displayed in a rectangular shape by using a projective transformation technique is used.

  In a projector that generates image light representing an image using a liquid crystal panel, an image distorted in the opposite direction to the projected image on the projection surface (hereinafter also referred to as a corrected image) when correcting trapezoidal distortion, Produced on a liquid crystal panel. That is, the image formed on the liquid crystal panel is a rectangular image that is distorted into a trapezoid, a parallelogram, and other rectangles. When a distorted image formed on a liquid crystal panel is displayed in a rectangular shape on the projection surface, the magnification on the image formed on the liquid crystal panel in the image displayed on the projection surface is different. Unevenness of brightness occurs in the displayed video. On the other hand, a technique for changing the upper limit of luminance has been proposed (see, for example, Patent Document 1).

JP 2000-196978 A

  However, the technique described in Patent Document 1 has found a problem that the brightness of the video after the trapezoidal distortion correction is darker than that of the original video.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 A projector that projects and displays an image on a projection surface,
A distortion-corrected video data generation unit that generates distortion-corrected video data by performing distortion correction processing for correcting distortion of an image projected on the projection surface with respect to the original video data input to the projector; ,
A deformation rate deriving unit for deriving a deformation rate corresponding to a relative size of the image after distortion correction with respect to the original image represented by the original image data, with respect to the image after distortion correction represented by the image data after distortion correction;
A luminance correction unit that generates luminance-corrected video data by correcting the luminance of the video data after distortion correction based on the deformation rate derived by the deformation rate deriving unit, the smaller the deformation rate, the lower the deformation rate. A brightness correction unit that performs the brightness correction so that an increase in brightness due to the brightness correction is increased;
A video light output unit that generates and outputs video light representing the video based on the brightness correction video data;
A projector comprising:

  Since the deformation rate corresponds to the relative size of the distortion-corrected image with respect to the original image represented by the original image data, a small deformation rate means that the reduction rate of the corrected image with respect to the original image is large. It is. A portion having a large reduction ratio in the image plane has a long optical path length, and therefore the image becomes dark unless luminance correction is performed. According to this configuration, the luminance correction is performed so that the increase in luminance due to the luminance correction increases as the deformation rate decreases, so that it is possible to increase the brightness of a portion that may be dark in the video screen.

[Application Example 2] In the projector described in Application Example 1,
As a result of performing the brightness correction, the brightness correction unit has a difference in brightness of an image of a portion having a small deformation rate before and after the distortion correction is smaller than a predetermined value in an image displayed on the projection surface. ,projector.
In this way, the brightness of the image after the trapezoidal distortion correction process projected on the projection surface does not decrease, and an image without a sense of incongruity can be obtained.

[Application Example 3] In the projector described in Application Example 2,
The brightness correction unit performs the brightness correction so that the brightness of an image displayed on the projection surface is the same before and after the distortion correction.
In this way, the influence of luminance correction due to distortion correction is not felt, and a more preferable image can be obtained.

[Application Example 4] In the projector described in Application Example 2 or Application Example 3,
The brightness correction unit performs the brightness correction so that a difference in brightness of an image displayed on the projection surface is within a predetermined range.
In such a projector, the brightness of the image on the projection surface is sufficiently secured, and the unevenness in the projection surface is within a predetermined range.

[Application Example 5] In the projector according to any one of Application Examples 1 to 4,
The deformation rate deriving unit derives the deformation rate for each pixel of the corrected image. According to this configuration, optimal brightness correction can be performed for each pixel, and thus a more appropriate corrected image can be obtained.

  Note that the present invention can be realized in various modes. For example, it can be realized in a manner such as a method of projecting an image from a projector or a luminance correction method in the projector.

It is explanatory drawing which shows a trapezoid distortion correction | amendment notionally. It is explanatory drawing which shows the image | video displayed on the liquid crystal panel part 192 before and behind correction | amendment. It is a schematic diagram which shows notionally the method of pixel interpolation. 1 is a block diagram schematically showing a configuration of a projector as an embodiment of the present invention. 3 is a functional block diagram illustrating a configuration of a trapezoidal distortion correction unit 120. FIG. It is process drawing which shows typically the flow of a brightness | luminance correction | amendment video data generation process. It is explanatory drawing which shows the change of the coordinate of the image | video before and after trapezoid distortion correction. It is a graph which shows an example of the relationship between a deformation rate and a brightness | luminance correction curve. It is a graph which shows the relationship between luminance increase (alpha) and deformation | transformation rate in the brightness | luminance before correction | amendment = 192.

Next, embodiments of the present invention will be described in the following order based on examples.
A. First embodiment:
A-1. Overview of keystone correction:
A-2. Projector configuration:
A-3. Keystone distortion correction section:
A-4. Flow of brightness correction data generation processing:
A-5. Calculation of deformation rate:
A-6. Brightness correction table:
A-7. Effects of the embodiment:
B. Variations:

A. Example:
A-1. Overview of keystone correction:
The projector 100 as one embodiment of the present invention projects image light representing an image and displays the image on a projection surface such as a screen SC. The projector 100 is a projector capable of correcting a trapezoidal distortion of a video displayed on the screen SC and displaying a rectangular video when a rectangular video is input. Prior to the description of the configuration of the projector 100, an outline of trapezoidal distortion correction in the projector 100 of the present embodiment will be briefly described.

  FIG. 1 is an explanatory diagram conceptually showing trapezoidal distortion correction. As shown in the figure, when the projector 100 is arranged with an inclination in the horizontal direction (left-right direction) and the vertical direction (up-down direction) with respect to the screen SC, it is displayed on the liquid crystal panel unit 192. The video (pre-correction video IG0) is rectangular, whereas the video PIG0 projected on the screen SC has a trapezoidal distortion in each of the horizontal and vertical directions. In FIG. 1, for convenience of explanation, the liquid crystal panel unit 192 included in the projector 100 is displayed outside the projector 100.

  Therefore, if a video image distorted in the opposite direction to the image projected on the screen SC (an image IG1 after trapezoidal distortion correction) is formed on the liquid crystal panel unit 192 using the projective transformation technique, a rectangular shape is formed on the screen SC. Video PIG1 is displayed (FIG. 1). In this way, correction for making a video having a trapezoidal distortion appear rectangular (the shape of the video that should be originally displayed) is called a trapezoidal distortion correction. The pre-correction video IG0 in this embodiment corresponds to the original video in the claims, and the trapezoidal distortion corrected video IG1 corresponds to the post-transformation video in the claims. Further, the trapezoidal distortion correction process in the present embodiment corresponds to the deformation process in the claims.

  FIG. 2 is an explanatory diagram showing images displayed on the liquid crystal panel unit 192 before and after correction. FIG. 2A shows an image IG0 before correction, and FIG. 2B shows an image IG1 after trapezoidal distortion correction. A broken line in FIG. 2B indicates the outer shape of the image IG0 before correction. Since the pre-correction video IG0 has been subjected to video processing so as to be displayed on the full frame of the liquid crystal panel unit 192, the broken line in FIG. 2B indicates the frame of the liquid crystal panel unit 192.

  In the present embodiment, the coordinates of the pre-correction video IG0 and the post-correction video IG1 are pixel coordinates when the pre-correction video IG0 and the post-correction video IG1 are displayed on the liquid crystal panel unit 192. Hereinafter, the pixel coordinates of the liquid crystal panel unit 192 when the image IG1 after trapezoidal distortion correction is displayed are referred to as corrected coordinates. Of the pixel coordinates of the liquid crystal panel unit 192, the pixel coordinates of the region where the image IG1 after trapezoidal distortion correction is not displayed are also referred to using the corrected coordinates. The coordinates obtained by converting the corrected coordinates to the coordinate positions (pixel coordinates of the liquid crystal panel) in the pre-correction video IG0 by reverse projection conversion are referred to as pre-correction coordinates.

  Since the pre-correction image IG0 and the trapezoidal distortion corrected image IG1 do not have an integer multiple correspondence, the calculated pre-correction coordinates include decimals. Therefore, in order to obtain the pixel value of the coordinate after correction, the pixel value of the coordinate before correction is estimated using the pixel value of 16 coordinates near the coordinate before correction. This is called pixel interpolation. That is, the trapezoidal distortion corrected image data representing the trapezoidal distortion corrected image IG1 is created by performing pixel interpolation for each pixel of the pixel values (coordinates) constituting the trapezoidal distortion corrected image IG1. The

  When trapezoidal distortion correction is performed, as shown in FIG. 2 (b), in the image IG1 after trapezoidal distortion correction, the vicinity of the vertex (X1, Y1) has a high reduction rate with respect to the image IG0 before correction (that is, the deformation rate is high). In the vicinity of the vertex (X3, Y3), the reduction ratio with respect to the pre-correction image IG0 is low (that is, the deformation ratio is large). As described above, the deformation rate of the trapezoidal distortion corrected image IG1 varies depending on the coordinates of the trapezoidal distortion corrected image IG1.

  As described above, the image IG1 after the trapezoidal distortion correction has a different deformation rate depending on the coordinates of the image IG1 after the image trapezoidal distortion correction. Therefore, in the projector 100 according to the present embodiment, the keystone distortion is generated for each pixel coordinate of the liquid crystal panel unit 192. A deformation rate of the corrected image IG1 with respect to the uncorrected image IG0 is calculated, and luminance correction is performed on the interpolated pixels subjected to the trapezoidal distortion correction process based on the calculated deformation rate to generate luminance corrected image data. (It will be described in detail later).

  FIG. 3 is a schematic diagram conceptually showing a pixel interpolation method. FIG. 3 illustrates a method of obtaining the pixel value of the uncorrected coordinate P0 (x, y) obtained by converting the corrected coordinate P1 (X, Y) by pixel interpolation. In the figure, the pre-correction coordinates P0 (x, y) are indicated by hatched circles, and the surrounding 16 coordinates are indicated by white circles. Since the pixel value of the pre-correction coordinate P0 (x, y) is obtained by pixel interpolation, the pixel value of the pre-correction coordinate P0 (x, y) is “interpolated pixel”, and the pixel values of the surrounding 16 coordinates are the pre-correction video data. Since it is known, it is also called “known pixel”.

  In FIG. 3, pixel values of 16 pixels that are known pixels are represented by DATA [m] [n] (m = 0, 1, 2, 3 (x direction); n = 0, 1, 2, 3 (y direction). ). The interpolation pixel is obtained by a convolution operation of the pixel value of 16 pixels and the filter coefficient. In this embodiment, when the pixel value of the interpolation pixel is obtained, the pixel value of the target pixel is obtained by performing horizontal interpolation after performing horizontal interpolation using 16 pixels around the target pixel. The filter coefficient is the distance between the interpolation pixel and the known pixel (for example, the distance between the known pixel of DATA [1] [1] and the interpolation pixel is dx in the horizontal direction (x direction) and dy in the vertical direction (y direction). It is a coefficient that takes into account the effects of

A-2. Projector configuration:
FIG. 4 is a block diagram schematically showing a configuration of a projector as an embodiment of the present invention. As illustrated, the projector 100 includes a video input unit 110, an IP conversion unit 112, a resolution conversion unit 114, a video synthesis unit 116, a trapezoidal distortion correction unit 120, a liquid crystal panel drive unit 140, and a frame buffer 150. A high-speed bus control unit 160, a low-speed bus control unit 162, a processor unit 170, an imaging unit 180, a sensor unit 182, an illumination optical system 190, a liquid crystal panel unit 192, and a projection optical system 194. It is structured in the center. Among the components described above, the components other than the illumination optical system 190, the liquid crystal panel unit 192, and the projection optical system 194 are connected to each other via the high-speed bus 102 or the low-speed bus 104.

  The video input unit 110 performs A / D conversion on an input video signal input from a DVD player or personal computer (not shown) via a cable, if necessary, and supplies the digital video signal to the IP conversion unit 112.

  The IP conversion unit 112 executes processing for converting the format of the video data supplied from the video input unit 110 from the interlace method to the progressive method, and supplies the obtained video data to the resolution conversion unit 114.

  The resolution conversion unit 114 performs a size enlargement process or a reduction process (that is, resolution conversion process) on the video data supplied from the IP conversion unit 112, and supplies the obtained video data to the video synthesis unit 116. To do.

  The video composition unit 116 synthesizes the video data supplied from the resolution conversion unit 114 and an OSD (On Screen Display) such as a menu screen, and writes the resultant data in the frame buffer 150 as pre-correction video data.

  The frame buffer 150 can store data of one frame or a plurality of frames. In this embodiment, an inexpensive and large-capacity DRAM (Dynamic Random Access Memory) is used as the frame buffer 150. The frame buffer 150 in this embodiment corresponds to a frame video storage unit in the claims.

  The trapezoidal distortion correction unit 120 corrects trapezoidal distortion that occurs when projection is performed with the projection axis of the projector 100 tilted with respect to the screen SC, and performs luminance correction based on the above-described deformation rate. Specifically, since the pre-correction video represented by the pre-correction video data stored in the frame buffer 150 is displayed on the liquid crystal panel unit 192 in a shape that compensates for the keystone distortion, the keystone distortion correction is performed on the video data before correction. After processing, the trapezoidal distortion-corrected video data is generated, and the keystone-distortion corrected video data is further subjected to luminance correction based on the deformation rate and supplied to the liquid crystal panel driving unit 140 as luminance-corrected video data. The trapezoidal distortion correction unit 120 will be described in detail later.

  The liquid crystal panel drive unit 140 drives the liquid crystal panel unit 192 based on the digital video signal input through the trapezoidal distortion correction unit 120. The liquid crystal panel unit 192 includes a transmissive liquid crystal panel in which a plurality of pixels are arranged in a matrix. The liquid crystal panel unit 192 is driven by the liquid crystal panel driving unit 140, and changes the light transmittance in each pixel arranged in a matrix, thereby changing the illumination light emitted from the illumination optical system 152 to an effective image. An image for modulation into a new image light is formed. In this embodiment, the mode of the liquid crystal panel unit 192 is WUXGA, and the resolution is 1920 × 1200 dots. In this embodiment, the liquid crystal panel pixel coordinates are defined as x = 0 to 1919 and y = 0 to 1199. The liquid crystal panel unit 192 may have a resolution different from that of this embodiment.

  The illumination optical system 152 includes, for example, lamps such as a high pressure mercury lamp and an ultrahigh pressure mercury lamp, and other light emitters. The projection optical system 194 is attached to the front surface of the housing of the projector 100, expands the light modulated into the image light by the liquid crystal panel unit 192, and projects it onto the screen SC. The projection optical system 194 includes a zoom lens (not shown), and can change the degree of enlargement (zoom state) when projecting light transmitted through the liquid crystal panel unit 192. The liquid crystal panel driving unit 140, the liquid crystal panel unit 192, the illumination optical system 190, and the projection optical system 194 in this embodiment correspond to the image light output unit in the claims.

  The processor unit 170 controls the operation of each unit in the projector 100 by reading and executing a control program stored in a storage unit (not shown). Further, corrected coordinates (X0 to X3, Y0 to Y3) described later based on the captured image captured by the imaging unit 180, the tilt of the projector 100 detected by the sensor unit 182 and the instruction from the user (see FIG. 2), a coordinate conversion coefficient (described in detail later) of the coordinate conversion matrix is calculated and output to the trapezoidal distortion correction unit 120. In addition, the processor unit 170 outputs a luminance correction table used for luminance correction performed by the trapezoidal distortion correction unit 120 to the trapezoidal distortion correction unit 120. In this embodiment, the processor unit 170 is configured to receive an instruction from the user through an operation panel (not shown) provided in the main body of the projector 100. For example, the instruction from the user through a remote control is controlled by the remote controller. The processor unit 170 may receive the instruction from the user via the low-speed bus 104.

  The imaging unit 180 has a CCD camera and generates a captured video. The captured video generated by the imaging unit 180 is stored in a captured video memory (not shown). Note that the imaging unit 180 may have another imaging device instead of the CCD camera.

  The sensor unit 182 can detect the tilt angle formed by the CCD optical axis of the imaging unit 180 and the horizontal plane by detecting the tilt of the projector 100 from the vertical direction.

A-3. Keystone distortion correction section:
As described above, the trapezoidal distortion correction unit 120 generates video data after correcting trapezoidal distortion by correcting the video before correction represented by the video data before correction stored in the frame buffer 150 into a shape that compensates for trapezoidal distortion. Then, the luminance correction is performed on the video data after the keystone distortion correction to generate the luminance corrected video data. FIG. 5 is a functional block diagram illustrating a configuration of the trapezoidal distortion correction unit 120. Interpolation block generation unit 121, pixel interpolation unit 122, first color conversion unit 123, luminance correction unit 124, second color conversion unit 125, FIFO unit 126, register unit 127, and control unit 128 And a coordinate conversion unit 129, a local deformation rate calculation unit 130, and a filter coefficient calculation unit 131.

  The control unit 128 controls the trapezoidal distortion correction unit 120 in general. For example, a frame start signal indicating the start of a frame is output to the coordinate conversion unit 129 in accordance with the synchronization signal input to the control unit 128. For example, when 60 frames are displayed per second, the synchronization signal is input every 1/60 seconds.

  The register unit 127 stores parameters supplied from the processor unit 170. Specifically, the register unit 127 stores parameters such as the frame width and frame height of one frame of the pre-correction video, the coordinate conversion coefficients A to H of the coordinate conversion matrix, and the luminance correction table. The brightness correction table will be described later. The coordinate conversion coefficients A to H are calculated by the processor unit 170 using the following determinant (formula 1) of projective transformation. Specifically, the processor unit 170 converts the uncorrected coordinates (x0 to x3, y0 to y3) (see FIG. 2) into the corrected coordinates (X0 to X3, Y0 to Y3) (see FIG. 2) by projective transformation. As converted, the four coordinates (X0 to X3, Y0 to Y3) of the image IG1 after trapezoidal distortion correction are input to the determinant (formula 1) to derive the coordinate conversion coefficients A to H, and the register Stored in the unit 127.

  In this embodiment, the image PIG0 displayed on the screen SC before the trapezoidal distortion correction is imaged by the imaging unit 180 before the generation process of the video data after the keystone distortion correction is started. The processor unit 170 (FIG. 4) determines the coordinates (X0 to X3, Y0 to Y3) (FIG. 2B) of the four vertices in the trapezoidal distortion corrected image IG1 based on the captured image. Looking for.

  Note that the sensor unit 182 may detect the inclination of the projector 100 from the vertical direction, and obtain corrected coordinates (X0 to X3, Y0 to Y3) based on the detected angle. Further, the keystone distortion correction may be manually performed by the user operating a key such as a remote controller. In such a case, the processor unit 170 obtains corrected coordinates (X0 to X3, Y0 to Y3) based on an instruction from the user received via the remote control unit.

  The coordinate conversion unit 129 uses the coordinate conversion coefficients A to H supplied from the register unit 127 and the following (Equation 2) and (Equation 3), and after the trapezoidal distortion correction image IG1 after the keystone distortion correction is performed. Are converted into coordinate values (pre-correction coordinates) of the pre-correction video IG0 (rectangular video), and the pre-correction coordinates are supplied to the local deformation rate calculation unit 130. Since the pre-correction image IG0 and the trapezoidal distortion corrected image IG1 do not have an integer multiple correspondence, the pre-correction coordinates calculated by the coordinate conversion unit 129 include decimals.

  Here, the above-described calculation method of the pre-correction coordinates will be described. Since the image IG1 after correcting the trapezoidal distortion is considered to be an image obtained by projective transformation of the image IG0 before correction, the coordinates before correction are the following (Expression 2) and (Expression 3) with respect to the corrected coordinates. Based on the above, it is calculated by performing reverse projection transformation. It is assumed that the uncorrected coordinates (x, y) are converted to corrected coordinates (X, Y) by projective transformation.

  The coefficients A to H in the above (Expression 2) and (Expression 3) are supplied from the processor unit 170 and stored in the register unit 127.

  The local deformation rate calculation unit 130 divides the coordinates before correction supplied from the coordinate conversion unit 129 into an integer part (integer coordinates) and a decimal part (decimal coordinates), and supplies the integer coordinates to the interpolation block generation unit 121. The decimal coordinates are supplied to the filter coefficient calculation unit 131. Further, the local deformation rate calculation unit 130 calculates the deformation rate of the image IG1 after correction of the trapezoidal distortion with respect to the image IG0 before correction based on the coordinates before correction supplied from the coordinate conversion unit 129, and supplies the deformation rate to the luminance correction unit 124. To do. The method for calculating the deformation rate will be described in detail later.

  The filter coefficient calculation unit 131 selects, from the filter coefficient table, a filter coefficient used when executing the pixel interpolation process based on the decimal coordinates supplied from the local deformation rate calculation unit 130, and selects the selected filter coefficient. This is supplied to the pixel interpolation unit 122. The filter coefficient table is a table showing the relationship between the distance between the interpolation pixel and the known pixel shown in FIG. 3 and the filter coefficient, and a filter coefficient storage unit (not shown) included in the filter coefficient calculation unit 131 based on a pre-calculated result. Stored in

  The interpolation block generation unit 121 acquires and stores the pre-correction video data stored in the frame buffer 150 in units of cache blocks including 8 × 8 pixels. In addition, the interpolation block generation unit 121 uses 4 integers necessary for pixel interpolation in the pixel interpolation unit 122 based on the integer component of the coordinates before correction supplied from the local deformation rate calculation unit 130 (hereinafter also referred to as “integer coordinates”). An interpolation block composed of × 4 pixels is generated and supplied to the pixel interpolation unit 122.

  The pixel interpolation unit 122 performs pixel interpolation processing based on the interpolation block supplied from the interpolation block generation unit 121 and the filter coefficient (described later) supplied from the filter coefficient calculation unit 131, and performs interpolation pixel (trapezoidal distortion) The corrected pixel value (RGB color space) is obtained and supplied to the first color conversion unit 123.

  The first color conversion unit 123 converts the value of the interpolation pixel (video data after trapezoidal distortion correction) supplied from the pixel interpolation unit 122 from the RGB color space to a YUV (YCbCr) color space expressed by luminance and color difference. 1 color conversion is performed. Here, Y represents luminance, U represents color difference (Cb), and V represents color difference (Cr). The first color conversion is performed based on the following conversion formula (Formula 4), for example. The conversion formula used for the first color conversion is not limited to the following (formula 4), and various conversion formulas can be used according to the range of the video data value in the projector 100 and the like.

Y = 0.299R + 0.587G + 0.114B
U = −0.169R−0.331G + 0.500B + 128 (Formula 4)
V = 0.500R-0.419G-0.081B + 128

  The luminance correction unit 124 uses the luminance correction table (not shown) supplied from the register unit 127 to perform the local deformation rate calculation unit for the interpolation pixel (trapezoidal distortion corrected video data) converted into the YUV color space. Luminance correction is performed based on the horizontal deformation rate and vertical deformation rate supplied from 130, a correction pixel (luminance corrected video data (YUV)) is generated, and is supplied to the second color conversion unit 125.

  The second color conversion unit 125 performs a second color conversion for converting the correction pixels (luminance-corrected video data) supplied from the luminance correction unit 124 from the YUV color space to the RGB color space. To the liquid crystal panel driver 140 (FIG. 4). The second color conversion is performed based on the following conversion formula (Formula 5), for example. The conversion formula used for the first color conversion is not limited to the following (formula 5), and various conversion formulas can be used according to the range of the video data value in the projector 100 and the like.

R = 1.000Y + 1.402V + 179.456
G = 1.000Y−0.344U−0.714V + 135.424 (Formula 5)
B = 1.000Y + 1.772U-226.816

A-4. Flow of luminance correction video data generation processing:
FIG. 6 is a process diagram schematically showing the flow of the brightness correction video data generation process. In the trapezoidal distortion correction unit 120 according to the present embodiment, when a frame start signal is output from the control unit 128 (FIG. 5) and input to the coordinate conversion unit 129 (FIG. 5), luminance correction video data generation processing is started. .

  The coordinate conversion unit 129 (FIG. 5) determines whether or not a frame start signal has been input (step S102). The coordinate conversion unit 129 waits until the frame start signal is input (NO in step S102), and when the frame start signal is input (YES in step S102), as described above, the video after the trapezoidal distortion correction. The coordinates before correction (coordinates after correction) are transformed to obtain the coordinates before correction (step S104).

  When the pre-correction coordinates calculated by the coordinate conversion unit 129 are supplied to the local deformation rate calculation unit 130 (FIG. 5), the local deformation rate calculation unit 130 performs the trapezoidal distortion corrected image on the pre-correction image with respect to the pre-correction image. The deformation rate is calculated and supplied to the luminance correction unit 124, and the integer part of the coordinates before correction is supplied to the interpolation block generation unit 121 and the decimal part is supplied to the filter coefficient calculation unit 131 (step S105).

  When the integer part (integer coordinates) of the pre-correction coordinates is supplied from the local deformation rate calculation unit 130 to the interpolation block generation unit 121 (FIG. 5), the interpolation block generation unit 121 selects an interpolation block based on the supplied integer coordinates. Generated and supplied to the pixel interpolation unit 122 (step S106). On the other hand, the filter coefficient calculation unit 131 (FIG. 5) selects a filter coefficient from the filter coefficient table based on the decimal part (decimal coordinates) of the coordinates before correction obtained in step S <b> 104, and performs the pixel interpolation unit 122. Supply (step S108). The interpolation block generation process in the interpolation block generation unit 121 and the filter coefficient calculation process in the filter coefficient calculation unit 131 are performed at the same time. When both processes are completed, the process proceeds to step S110.

  When the interpolation block is supplied from the interpolation block generation unit 121 and the filter coefficient is supplied from the filter coefficient calculation unit 131, the pixel interpolation unit 122 (FIG. 5) performs convolution using the supplied interpolation block and filter coefficient. A pixel interpolation process is executed by calculation, and pixel values (R, G, B) of the interpolation pixels are calculated and supplied to the first color converter 123 (FIG. 5) (step S110).

  The first color conversion unit 123 performs color conversion for converting the supplied pixel values (R, G, B) of the interpolation pixels into pixel values in the YUV color space, and performs pixel values (Y, U, V) is supplied to the luminance correction unit 124 (FIG. 5) (step S112). When the pixel value (Y, U, V) of the interpolation pixel is supplied from the first color conversion unit 123, the luminance correction unit 124 receives the deformation rate (horizontal deformation rate, vertical) supplied from the local deformation rate calculation unit 130. Deformation rate) and luminance correction based on the luminance correction table supplied from the register unit 127, and supply the pixel value (Y, U, V) of the correction pixel to the second color conversion unit 125 (FIG. 5). (Step S114). The second color conversion unit 125 performs color conversion to convert the pixel value (Y, U, V) of the supplied correction pixel into a pixel value in the RGB color space, and the pixel value (R, G, B) is supplied to the FIFO unit 126 (FIG. 5) (step S116).

  By repeating the above steps S102 to S116 until the corrected coordinates (X, Y) = (0, 0) to (frame width −1, frame height −1), luminance corrected video data is generated. The In this embodiment, since the frame width is 1920 and the frame height is 1200, steps S102 to S116 are repeated until the corrected coordinates (X, Y) = (0, 0) to (1919, 1199). When the frame width and the frame height are different from those of the present embodiment, the steps S102 to S116 are performed after the corrected coordinates (X, Y) = (0, 0) to (frame width−1, frame height− By repeating the process up to 1), luminance corrected video data is generated.

  In addition, when a plurality of videos are continuously input (for example, when a moving image is input), the above processing may be repeated for each video to perform luminance correction, or the first As described above, the deformation rate is calculated for each coordinate for the image, and the calculated deformation rate is stored in the register unit 127. When the luminance correction is performed on the second and subsequent images, the image is stored in the register unit 127. Brightness correction may be performed using the deformed ratio. The former case is suitable for processing by hardware. In the latter case, the hardware configuration can be omitted by processing with software.

A-5. Calculation of deformation rate:
The local deformation rate calculation unit 130 (FIG. 5) converts, for each coordinate of the image after trapezoidal distortion correction, target coordinates for calculating a pixel value and its surrounding 8 coordinates into coordinates of the image before correction by reverse projection transformation. Thus, the deformation amount of the target coordinates is obtained.

  FIG. 7 is an explanatory diagram showing changes in the coordinates of an image before and after correcting trapezoidal distortion. FIG. 7A shows an image IG0 before correction, and FIG. 7B shows an image IG1 after trapezoidal distortion correction. As shown in FIG. 7B, the coordinates before correction, which are the results of converting the coordinates (a_x, a_y) in the post-trapezoidal distortion corrected image IG1 and the surrounding eight coordinates into the coordinates of the image IG0 before correction, are shown in FIG. It is shown in a). Hereinafter, the target coordinates for obtaining the deformation amount are also referred to as “target corrected coordinates”.

  In this embodiment, as shown in FIG. 7B, the coordinates after target correction of the image IG1 after trapezoidal distortion correction are (a_x, a_y), and the peripheral pixel coordinates are 8 pixels around the coordinates after target correction. Coordinates (a_x-1, a_y-1), (a_x + 0, a_y-1), (a_x + 1, a_y-1), (a_x-1, a_y + 0), (a_x + 1, a_y + 0), (a_x-1, a_y + 1), (A_x + 0, a_y + 1), (a_x + 1, a_y + 1). The pre-correction coordinates are calculated by the reverse projection transformation of the above-described projection transformation.

  The coordinates before correction calculated by the inverse projective transformation are represented by src (0,0), src (1,0), src (2,0), src (0,1), src (1) shown in FIG. , 1), src (2, 1), src (0, 2), src (1, 2), src (2, 2). That is, the coordinates after correction (a_x−1, a_y−1) → the coordinates before correction src (0,0), the coordinates after correction (a_x + 0, a_y−1) → the coordinates before correction src (1,0), the coordinates after correction ( a_x + 1, a_y-1) → pre-correction coordinates src (2,0), post-correction coordinates (a_x−1, a_y + 0) → pre-correction coordinates src (0,1), post-correction coordinates (a_x, a_y) → pre-correction coordinates src (1, 1), corrected coordinates (a_x + 1, a_y + 0) → corrected coordinates src (2,1), corrected coordinates (a_x−1, a_y + 1) → corrected coordinates src (0,2), corrected coordinates (A_x + 0, a_y + 1) → pre-correction coordinates src (1,2), post-correction coordinates (a_x + 1, a_y + 1) → pre-correction coordinates src (2,2).

  The local deformation rate calculation unit 130 calculates the horizontal distance between adjacent uncorrected coordinates shown in FIG. 7A to obtain the maximum value. Specifically, the horizontal distance between src (0,0) and src (1,0), the horizontal distance between src (1,0) and src (2,0),..., Src (1, The horizontal distance between 2) and src (2, 2) is calculated, the maximum value is obtained, and the maximum value is set as the horizontal deformation amount. As shown in FIG. 7B, since the horizontal distance between adjacent corrected coordinates is “1”, the local deformation rate calculation unit 130 sets the reciprocal of the horizontal deformation amount as the horizontal deformation rate. In the present embodiment, the deformation rate is calculated using the maximum horizontal distance between adjacent uncorrected coordinates, but an average value of adjacent horizontal distances between uncorrected coordinates may be used.

  Similarly, the vertical distance between adjacent uncorrected coordinates is calculated to determine the maximum value, and the maximum value is used as the vertical deformation amount. The local deformation rate calculation unit 130 sets the reciprocal of the vertical deformation amount as the vertical deformation rate.

  For example, when the coordinates in the vicinity of the upper right vertex of the image IG1 after trapezoidal distortion correction shown in FIG. 7B are the corrected coordinates (a_x, a_y), as shown in FIG. The maximum value of the horizontal distance of coordinates (horizontal deformation amount) = 2, and the horizontal deformation rate = 1/2. Further, as shown in FIG. 7A, the maximum value of the vertical distance between adjacent uncorrected coordinates (vertical deformation amount) = 2.3, and the vertical deformation ratio = 1 / (2.3).

A-6. Brightness correction table:
FIG. 8 is a graph showing an example of the relationship between the deformation rate and the luminance correction curve. The brightness correction table of the present embodiment has a relationship between the deformation rate and the brightness before and after correction as shown in FIG. In FIG. 8, the deformation rate is shown in the form of deformation rate (horizontal deformation rate, vertical deformation rate). For example, the deformation ratio (1.0, 1.0) means horizontal deformation ratio = 1.0 and vertical deformation ratio = 1.0. In this embodiment, as shown in FIG. 8, the luminance correction curve is set so that the amount of increase in luminance by luminance correction increases as the deformation rate decreases, that is, the reduction rate increases. This is because the larger the reduction ratio, the longer the optical path length and the darker the image projected on the screen SC. Therefore, the brightness of the image projected on the screen SC is increased by increasing the luminance of the pixels with a large reduction ratio. Because it can be raised.

  In the present embodiment, the luminance is not corrected when both the horizontal deformation rate and the vertical deformation rate are 1.0, that is, when there is no deformation (FIG. 8). On the other hand, when both the horizontal deformation rate and the vertical deformation rate are 0.8, 0.5, 0.1, that is, when the image is reduced, the luminance after correction is larger than the luminance before correction. (FIG. 8). Specifically, an increase α of the luminance value before correction = 192 (in FIG. 8, the increase α when the horizontal deformation rate and the vertical deformation rate are both 0.1 is illustrated), the deformation rate becomes small. It is increasing according to. In this embodiment, a curve equation connecting the three points is set as the luminance correction curve so that the luminance before correction = 0, 192, 255 becomes 0, 192 + α, 255 after correction, respectively. The curve connecting these three points is preferably obtained by cubic spline interpolation, but may be obtained by other interpolation methods such as Bezier interpolation and Lagrangian interpolation. In this embodiment, the value of α is obtained based on equation (4) described later. In this embodiment, the correction curve is set using three points, but may be set using four or more points.

  FIG. 9 is a graph showing the relationship between the luminance increase α and the deformation rate when luminance before correction = 192. The increase in luminance α is expressed by the following equation (6). This equation is obtained experimentally. Expression (6) is an expression having the deformation rate as a denominator, and the luminance increase amount α increases as the deformation rate decreases (FIG. 9). When the deformation rate is 1.0 or more, that is, when enlargement is performed, a saturation process is performed to set the deformation rate to 1.0. That is, when the horizontal deformation rate and the vertical deformation rate are both 1.0 or more, the luminance increase α = 0, and the luminance is not corrected. In the example shown in FIG. 9, the correction coefficient G (Rx, Ry) = 0.2 (fixed), but the value of the correction coefficient may be changed according to the deformation rate.

α: Brightness increase before correction = 192 Rx: Horizontal deformation rate Ry: Vertical deformation rate R: Either Rx or Ry G (Rx, Ry): Correction coefficient

A-7. Effects of the embodiment:
As described above, according to the projector 100 in the present embodiment, the luminance correction is performed as the deformation rate is smaller, that is, as the reduction rate is larger, with respect to the image data after the trapezoidal distortion correction by the trapezoidal distortion correction. Luminance correction is performed so that the increase in luminance due to is increased. For this reason, the brightness of the darkened portion of the image projected on the screen SC can be increased due to the positional relationship between the projector 100 and the screen SC, so that the brightness of the image projected on the screen SC after the trapezoidal distortion correction processing is reduced. Can be suppressed. This is because the portion where the reduction ratio of the image after the trapezoidal distortion correction with respect to the image before the correction is large is a portion having a long optical path length when projected onto the screen SC, and the brightness is optically reduced.

  In particular, if the difference between the brightness of the image at a small deformation rate before and after distortion correction is set to be smaller than a predetermined value, the brightness of the entire image can be sufficiently secured. Of course, if the brightness before and after the distortion correction is made equal regardless of the magnitude of the distortion correction, a bright image with no sense of incongruity can be projected.

B. Modifications The present invention is not limited to the above-described embodiments, and can be implemented in various modes without departing from the scope of the invention.

  (1) In the above-described embodiment, the luminance increase α at the pre-correction luminance = 192 is obtained using Expression (6), but the method of setting the luminance increase α is not limited to the above-described embodiment. The luminance increase α may be set so that the difference between the brightness of the video displayed on the screen SC before and after the trapezoidal distortion correction is within a predetermined range. Furthermore, it is preferable to set the difference to be zero. In other words, when the projector 100 is arranged so that the projector 100 faces the screen SC, an image without distortion (the keystone distortion correction is not performed) displayed on the screen SC, and after the keystone distortion correction is performed, the image is displayed on the screen SC. The luminance increase α may be set so that the brightness does not change from the image with the corrected distortion.

  (2) The number of pixels in one frame, the number of pixels in the cache block, and the number of pixels in the interpolation block (the number of pixels used for pixel interpolation) are not limited to the above embodiment.

  (3) In the above-described embodiment, the projector 100 modulates the light from the illumination optical system 152 using the transmissive liquid crystal panel unit 192, but is not limited to the transmissive liquid crystal panel unit 192. For example, using a digital micromirror device (DMD (registered trademark): Digital Micro-Mirror Device), a reflective liquid crystal panel (LCOS (registered trademark): Liquid Crystal on Silicon), or the like, from the illumination optical system 152. The light may be modulated. Further, it may be a CRT projector that projects an image on a small CRT (cathode ray tube) onto a projection surface, or may be configured to generate image light using an organic EL.

  (4) In the above embodiment, a part of the function realized by hardware may be realized by software, or a part of the function realized by software may be realized by hardware.

  (5) In the above embodiment, the trapezoidal distortion correction unit 120 calculates the deformation rate for each coordinate after correction, but the method for calculating the deformation rate is not limited to the above embodiment. For example, after trapezoidal distortion correction video is divided into blocks for each pixel (coordinates), the deformation rate is derived for each block, and the deformation rate corresponding to the block is applied to all pixels (coordinates) included in the block You may make it do.

  (6) In the above-described embodiment, when the deformation rate in the corrected coordinates is derived, the deformation rate is derived using 8 coordinates around the target corrected coordinates. It is not limited to the above-described embodiment. For example, the deformation rate may be derived using one coordinate (one coordinate each in the x direction and the y direction) adjacent to the target corrected coordinate.

  (7) In the above embodiment, the example in which the pixel value of the target pixel is obtained by performing horizontal interpolation after performing horizontal interpolation using 16 pixels around the target pixel is shown. ) And the interpolation distance in the vertical direction (y direction) may be used to perform pixel interpolation using a two-dimensional interpolation filter.

  (8) The projector in the above-described embodiment may be configured as an ultra-short focus projector. The smaller the deformation rate (the larger the reduction rate), the better the brightness of the video displayed on the screen SC when brightness correction is not performed.

DESCRIPTION OF SYMBOLS 100 ... Projector 102 ... High-speed bus 104 ... Low-speed bus 110 ... Video input part 112 ... IP conversion part 114 ... Resolution conversion part 116 ... Video composition part 120 ... Trapezoid distortion correction part 121 ... Interpolation block generation part 122 ... Pixel interpolation part 123 ... First color conversion unit 124 ... brightness correction unit 125 ... second color conversion unit 126 ... FIFO unit 127 ... register unit 128 ... control unit 129 ... coordinate conversion unit 130 ... local deformation rate calculation unit 131 ... filter coefficient calculation unit 140 DESCRIPTION OF SYMBOLS ... Liquid crystal panel drive part 150 ... Frame buffer 152 ... Illumination optical system 160 ... High speed bus control part 162 ... Low speed bus control part 170 ... Processor part 180 ... Imaging part 182 ... Sensor part 190 ... Illumination optical system 192 ... Liquid crystal panel part 194 ... Projection optical system PIG0 ... Video PIG1 ... Video SC ... Screen G0 ... corrected image IG1 ... trapezoidal distortion corrected image

Claims (6)

A projector that projects and displays an image on a projection surface,
A distortion-corrected video data generation unit that generates distortion-corrected video data by performing distortion correction processing for correcting distortion of an image projected on the projection surface with respect to the original video data input to the projector; ,
A deformation rate deriving unit for deriving a deformation rate corresponding to a relative size of the image after distortion correction with respect to the original image represented by the original image data, with respect to the image after distortion correction represented by the image data after distortion correction;
A luminance correction unit that generates luminance-corrected video data by correcting the luminance of the video data after distortion correction based on the deformation rate derived by the deformation rate deriving unit, the smaller the deformation rate, the lower the deformation rate. A brightness correction unit that performs the brightness correction so that an increase in brightness due to the brightness correction is increased;
A video light output unit that generates and outputs video light representing the video based on the brightness correction video data;
A projector comprising: The projector according to claim 1.
As a result of performing the brightness correction, the brightness correction unit has a difference in brightness of an image of a portion having a small deformation rate before and after the distortion correction is smaller than a predetermined value in an image displayed on the projection surface. ,projector. The projector according to claim 2.
The brightness correction unit performs the brightness correction so that the brightness of an image displayed on the projection surface is the same before and after the distortion correction. The projector according to claim 2 or 3,
The brightness correction unit performs the brightness correction so that a difference in brightness of an image displayed on the projection surface is within a predetermined range. The projector according to any one of claims 1 to 4,
The deformation rate deriving unit derives the deformation rate for each pixel of the corrected image. A method of projecting an image from a projector onto a projection surface,
A distortion correction process for correcting distortion of an image projected on the projection surface is performed on the original image data input to the projector to generate image data after distortion correction,
Deriving a deformation rate corresponding to the relative size of the distortion-corrected video with respect to the original video represented by the original video data for the distortion-corrected video represented by the distortion-corrected video data,
Based on the derived deformation rate, the brightness of the video data after distortion correction is corrected to generate brightness corrected video data, and the increase in brightness due to the brightness correction increases as the deformation rate decreases. Performing the brightness correction,
A projection method for generating and outputting image light representing the image based on the luminance-corrected image data.

Images