JP2007295542A - Output image adjustment of image data - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically adjust the image quality of image data without impairing the output tendency of arbitrary image processing applied to the image data. <P>SOLUTION: When image data GF include imaging information PI (Exif IFD), a CPU calculates a modified lightness correction amount tCurve-Y with an exposure correction amount (exposure amount) EV taken into account. Specifically, the modified lightness correction amount tCurve-Y is calculated by multiplying an original lightness correction amount tCurve-Yorg by 1/2¾EV¾. Accordingly, as the exposure correction amount increases, the modified lightness correction amount decreases like geometric series. The CPU applies the obtained modified lightness correction amount tCurve-Y to a tone curve and performs picture-quality adjustment including the lightness. That is, the modified lightness correction amount tCurve-Y is used to modify the tone curve characteristic, and the modified tone curve is applied to image data GD to adjust the picture quality of the image data. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image adjustment technique for adjusting the brightness of image data.

  The image quality of image data generated by a digital still camera (DSC), a digital video camera (DVC), a scanner, or the like can be arbitrarily adjusted by using an image retouching application on a personal computer. An image retouching application generally has an image adjustment function that automatically adjusts the image quality (characteristics) of image data. If this image adjustment function is used, the image quality of image data output from an output device is provided. Can be easily adjusted to a standard image quality. Known image data output devices include, for example, CRTs, LCDs, printers, projectors, and television receivers.

  Also, a printer driver that controls the operation of a printer, which is one of output devices, has a function of automatically adjusting the image quality (characteristics) of image data. The image quality of the image data to be printed can be easily adjusted to the standard image quality.

JP 2001-243463 A

  Usually, in the automatic image quality adjustment function provided by these image retouching applications and the like, image quality correction based on the image quality of standard image data is executed. On the other hand, since image data to be subjected to image processing can be generated under various conditions, the image quality (characteristics) of the image data is uniformly determined by the automatic image quality adjustment function using a reference value assuming standard image data. ) May not be able to be corrected properly.

  Some image data generation apparatuses such as DSC can arbitrarily adjust the image quality of image data when generating the image data, and the user can intentionally generate image data having a predetermined image quality. When the automatic image quality adjustment function is executed for such image data, even the intentional image characteristics of the image data are uniformly adjusted based on the reference value, and an output image reflecting the user's intention is obtained. There was a problem that could not be obtained.

  SUMMARY An advantage of some aspects of the invention is to automatically adjust the image quality of image data without impairing the output tendency of arbitrary image processing performed on the image data.

  In order to solve the above problems, a first aspect of the present invention provides an image processing apparatus that executes image processing on image data using image data and an exposure correction amount for the image data. The image processing apparatus according to the first aspect of the present invention includes a correction amount determination unit that determines a lightness correction amount of the image data using a lightness reference value that is a reference for image quality adjustment relating to lightness, and the exposure correction amount is large. A correction amount correction unit that decreases the lightness correction amount as it becomes, and an image quality adjustment unit that adjusts the lightness of the image data by applying the corrected lightness correction amount.

  According to the image processing apparatus of the first aspect of the present invention, the brightness correction amount of the image data is determined using the brightness reference value that is a reference for the image quality adjustment relating to the brightness, and the determined brightness correction amount is used as the exposure correction amount. Since the brightness of the image data is adjusted by applying a corrected brightness correction amount, the image quality of the image data is automatically adjusted without impairing the output conditions relating to the arbitrarily set brightness. be able to. Therefore, even when the image quality is automatically adjusted, if a bright output result is intended, a bright output result can be obtained, and if a dark output result is intended, it is dark. An output result can be obtained.

  In the image processing apparatus according to the first aspect of the present invention, the correction amount correction unit includes a degree of change in the brightness correction amount with respect to the exposure correction amount that is less than a predetermined exposure correction amount, and at least the predetermined exposure correction amount. The degree of change in the lightness correction amount with respect to the exposure correction amount may be different. Alternatively, the correction amount correction unit may decrease the reduction rate of the brightness correction amount as the exposure correction amount increases. By providing such a configuration, it is possible to maintain the gradation of highlights and shadow portions even when the exposure correction amount is large, and as a result, it is possible to prevent the occurrence of whiteout or blackout.

  In the image processing apparatus according to the first aspect of the present invention, the lightness correction amount may be reduced geometrically. In such a case, even if the image quality is automatically adjusted, if a bright output result is intended, a bright output result can be obtained more accurately, and a dark output result is intended. If it is, a dark output result can be obtained more accurately. For example, the correction amount correction unit may correct the lightness correction amount by dividing the lightness correction amount by an exponential function using the exposure correction amount as a parameter. In such a case, the lightness correction amount can be reduced geometrically as the exposure correction amount increases.

  The image processing apparatus according to the first aspect of the present invention further includes a lightness characteristic value acquisition unit that analyzes the image data and acquires a lightness characteristic value indicating characteristics relating to the lightness of the image data, and determines the correction amount. The unit may determine the lightness correction amount so as to reduce a deviation between the lightness reference value and the acquired lightness characteristic value. In such a case, the characteristics relating to the brightness of the image data can be corrected more appropriately based on the characteristics of the individual image data.

  The image processing apparatus according to the first aspect of the present invention further includes an input unit for inputting a lightness correction tendency for the image data, and the correction amount determination unit is based on the input lightness correction tendency. Then, the brightness correction amount of the image data may be determined. In such a case, the characteristics relating to the brightness of the image data can be corrected more appropriately based on the input tendency of brightness correction.

  The image processing apparatus according to the first aspect of the present invention may further include an image output unit that outputs an image using the image data adjusted in brightness. In such a case, it is possible to output an image with corrected characteristics relating to brightness.

  In the image processing apparatus according to the first aspect of the present invention, the correction amount correction unit corrects the brightness correction amount in consideration of a luminance difference before and after contrast correction, and the image data and the exposure correction amount are: It may be stored in the same file. In such a case, the influence on brightness by contrast correction can be compensated. In addition, it is possible to easily associate the exposure correction amount with the image data.

  A second aspect of the present invention provides an image processing apparatus that executes image processing on image data using image data and information on exposure correction performed on the image data. An image processing apparatus according to a second aspect of the present invention comprises: a lightness characteristic value acquisition unit that analyzes the image data and acquires a lightness characteristic value indicating characteristics related to the lightness of the image data; and a reference for image quality adjustment related to lightness The image quality adjustment unit that reduces the deviation between the brightness reference value and the acquired brightness characteristic value, and the exposure correction performed on the image data based on the exposure correction information increases as the degree of exposure correction increases. And a deviation reduction amount adjusting unit for reducing the degree of deviation reduction.

  According to the image processing apparatus of the second aspect of the present invention, when reducing the deviation between the lightness reference value that is a reference for image quality adjustment related to lightness and the acquired lightness characteristic value, based on exposure correction information, Since the degree of deviation reduction is reduced as the degree of exposure correction performed on the image data increases, it is possible to automatically adjust the image quality of the image data without impairing the output conditions relating to the arbitrarily set brightness. it can. Therefore, even when the image quality is automatically adjusted, if a bright output result is intended, a bright output result can be obtained as intended, and a dark output result is intended. In this case, a dark output result can be obtained as intended. Note that the degree of deviation reduction may be reduced geometrically. In such a case, when a bright output result is intended, a bright output result can be obtained more precisely according to the intention, and when a dark output result is intended, it can be more accurately intended. A dark output result can be obtained along.

  The image processing apparatus according to the second aspect of the present invention is also realized as a method and a program in addition to this, and is realized in various aspects in the same manner as the image processing apparatus according to the first aspect of the present invention. Can be done.

  A third aspect of the present invention provides an image processing method for image data using image data and an exposure correction amount for the image data. The image processing method according to the third aspect of the present invention determines a lightness correction amount of the image data using a lightness reference value that is a reference for image quality adjustment relating to lightness, and the lightness correction as the exposure correction amount increases. The amount is corrected to be small, and the lightness correction amount is applied to adjust the lightness of the image data.

  According to the image processing method of the third aspect of the present invention, it is possible to obtain the same operational effects as those of the image processing apparatus according to the first aspect of the present invention. The image processing method according to the third aspect of the present invention can be realized in various aspects in the same manner as the image processing apparatus according to the first aspect of the present invention.

  According to a fourth aspect of the present invention, there is provided a computer-readable recording medium on which an image processing program for executing image processing on image data using image data and an exposure correction amount for the image data is recorded. An image processing program recorded on a computer-readable recording medium according to a fourth aspect of the present invention has a function of determining a lightness correction amount of the image data using a lightness reference value that is a reference for image quality adjustment relating to lightness. And a computer that realizes a function of correcting the brightness correction amount to be smaller as the exposure correction amount is increased and a function of adjusting the brightness of the image data by applying the corrected brightness correction amount. To do.

  According to the computer-readable recording medium on which the image processing program according to the fourth aspect of the present invention is recorded, the same operational effects as those of the image processing apparatus according to the first aspect of the present invention can be obtained. Further, the computer-readable recording medium recording the image processing program according to the fourth aspect of the present invention can be realized in various aspects in the same manner as the image processing apparatus according to the first aspect of the present invention. .

  According to a fifth aspect of the present invention, there is provided an image processing apparatus that executes image processing on image data associated with shooting information indicating shooting conditions at the time of shooting. An image processing apparatus according to a fifth aspect of the present invention analyzes an acquired image data, acquires an image quality characteristic value indicating an image quality characteristic of the image data, and the acquired image data A search unit for searching for shooting information indicating a shooting intention from the shooting information associated with the image quality, and a deviation between a predetermined image quality adjustment reference value for image quality adjustment and the acquired image quality characteristic value is reduced. If the image quality adjustment unit that adjusts the image quality of the image data and the shooting information indicating the shooting intention can be detected, the deviation reduction can be performed using the searched shooting information indicating the shooting intention. And a deviation reduction amount adjusting unit for adjusting the degree.

  According to the image processing device of the fifth aspect of the present invention, the degree of deviation reduction during the image quality adjustment process is adjusted using the shooting information indicating the shooting intention among the shooting information indicating the shooting conditions at the time of shooting. Therefore, it is possible to execute image quality adjustment processing that reflects the shooting intention.

  In the image processing device according to the fifth aspect of the present invention, when the shooting information indicating the shooting intention cannot be detected, the degree of reduction of the deviation is adjusted depending on the shooting information indicating the shooting intention. It does not have to be done. In such a case, the image quality adjustment process can be executed without using shooting information indicating the shooting intention.

  The fifth aspect of the present invention can also be realized in the form of a recording medium on which a method and a program are recorded.

  Hereinafter, an image processing apparatus according to the present invention will be described based on examples with reference to the drawings.

A. Image processing system configuration:
The configuration of an image processing system to which the image processing apparatus according to this embodiment can be applied will be described with reference to FIGS. FIG. 1 is an explanatory diagram illustrating an example of an image processing system to which the image processing apparatus according to the present embodiment can be applied. FIG. 2 is a block diagram illustrating a schematic configuration of a digital still camera capable of generating image data to be processed by the image processing apparatus according to the present embodiment. FIG. 3 is a block diagram illustrating a schematic configuration of a color printer that functions as an image processing apparatus according to the present embodiment.

  The image processing system 10 includes a digital still camera 12 as an input device that generates image data, a personal computer PC as an image processing device that performs image processing on image data generated by the digital still camera 12, and an image A color printer 20 is provided as an output device for outputting. As the output device, in addition to the printer 20, a monitor 14 such as a CRT display or LCD display, a projector, or the like can be used. In the following description, the color printer 20 is used as the output device.

  The digital still camera 12 is a camera that electrically acquires an image by imaging light information on a digital device (CCD or photomultiplier tube). As shown in FIG. 2, a CCD for collecting optical information is used. And the like, an image acquisition circuit 122 for acquiring an image by controlling the optical circuit 121, an image processing circuit 123 for processing the acquired digital image, and a memory for temporarily storing each data And a control circuit 124 for controlling each circuit. The digital still camera 12 stores the acquired image as digital data in a storage device such as the memory card MC. As a storage format of image data in the digital still camera 12, a JPEG format is generally used, but other storage formats such as a RAW format, a TIFF format, a GIF format, and a BMP format may be used.

  The digital still camera 12 has a selection / determination button 126 for setting a shooting mode, an exposure correction amount (exposure correction value), a light source, and the like, previews a shot image, and uses the selection / determination button 126 to set an exposure correction amount and the like. Is provided with a liquid crystal display 127. Since the appropriate exposure is automatically set in the digital still camera 12, the exposure correction amount set in the digital still camera 12 is set as a plus correction amount or a minus correction amount with respect to the appropriate exposure. The exposure correction amount is expressed by the exposure amount EV. When there is no exposure correction, EV is set to ± 0. When the exposure is to be corrected brightly with respect to the appropriate exposure, +0.1 EV and +2.0 EV. When the exposure correction amount is set on the plus side as in the above and it is desired to correct the exposure to be dark with respect to the appropriate exposure, the exposure correction amount is set on the minus side, such as -0.1 EV and -2.0 EV.

  The digital still camera 12 used in the image data output system 10 stores shooting information PI of image data as an image file GF in the memory card MC in addition to the image data GD. That is, the shooting information PI is automatically stored in the memory card MC as an image file GF together with the image data GD at the time of shooting. For example, when shooting parameters such as exposure correction amount and light source are set to arbitrary values by the user, the image data GD generated according to the set exposure correction amount and the values of the set parameters are described. The image file GF including the captured image information PI is stored in the memory card MC.

  The image file GF generated in the digital still camera 12 is sent to the color printer 20 via, for example, the cable CV, the computer PC, or via the cable CV. Alternatively, the memory card MC in which the image file GF is stored by the digital still camera 12 is connected to the printer 20 via the computer PC mounted in the memory card slot or directly to the printer 20. As a result, the image file is sent to the color printer 20. In this embodiment, the case where the color printer 20 executes image processing and output (printing) processing in a stand-alone manner will be described.

  A color printer 20 shown in FIG. 3 is a printer capable of outputting a color image. For example, four color inks of cyan (C), magenta (M), yellow (Y), and black (K) are used as a printing medium. This is an ink jet printer that forms an image by forming a dot pattern by jetting it upward. Alternatively, it is an electrophotographic printer that forms an image by transferring and fixing color toner onto a printing medium. In addition to the above four colors, light cyan (light cyan, LC), light magenta (light magenta, LM), and dark yellow (dark yellow, DY) may be used as the color ink.

  The color printer 20 includes a printing unit 21 that includes a print head or a rotating drum and executes a printing process on a printing medium, a slot 22 that accommodates a memory card MC, and a control circuit 23 that controls the operation of each unit of the color printer 20. I have. The control circuit 23 includes an arithmetic processing unit (CPU) 231 that executes various arithmetic processes, a read-only memory (ROM) 232 that stores programs executed by the CPU 231 in a nonvolatile manner, arithmetic processing results in the CPU 231, and acquired A random access memory (RAM) 233 for temporarily storing data is provided. The control circuit 23 analyzes the shooting information PI read from the memory card MC, and controls the movement of a paper feed motor, carriage motor, print head, etc. (not shown) based on the analyzed shooting information PI.

B. Image file structure:
The image file GF according to the present embodiment can have a file structure in accordance with, for example, a digital still camera image file format standard (Exif). Exif file specifications are defined by the Japan Electronics and Information Technology Industries Association (JEITA). JPEG-Exif files that store compressed JPEG data as image data, and TIFF-Exif files that store uncompressed TIFF data. Exists. In the following description, a compressed file, that is, a JPEG-Exif file will be used.

  A schematic configuration of an image file according to an Exif format that can be used in the present embodiment will be described with reference to FIG. FIG. 4 is an explanatory diagram showing a schematic internal structure of the image file GF according to the Exif format. Note that terms such as file structure, data structure, and storage area in this embodiment mean an image of a file or data in a state where the file or data is stored in the storage device.

  The image file GF includes an SOI marker segment 101 indicating the head of the compressed data, an APP1 marker segment 102 that stores Exif attached information, an APP2 marker segment 103 that stores Exif extension data, a DQT marker segment 104 that defines a quantization table, DHT marker segment 105 that defines the Huffman table, DRI marker segment 106 that defines the insertion interval of the restart marker, SOF marker segment 107 that indicates various parameters related to the frame, SOS marker segment 108 that indicates various parameters related to the scan, and compressed data It includes an EOI marker segment 109 indicating the end. The compressed image data GD is stored in the image data storage area 110 between the SOS marker segment 108 and the EOI marker segment 109. The recording order of each marker segment is arbitrary except that the APP1 and APP2 marker segments are recorded immediately after the SOI marker segment, and the SOS marker segment is recorded with the image data interposed immediately before the EOI marker segment.

  The APP1 marker segment 102 includes an APP1 marker 1021, an Exif identification code 1022, attached information 1023, and a thumbnail image 1024. The attached information takes a TIFF structure including a file header (TIFF header), and Exif-JPEG stores Exif-specific attached information including 0th IFD for storing attached information related to compressed image data and shooting information PI. An Exif IFD and a 1st IFD for storing auxiliary information related to thumbnail images are included. The Exif IFD is pointed by an offset from the TIFF header stored in the 0th IFD. In IFD, a tag is used to identify each piece of information, and each piece of information is sometimes called by a tag name.

  The shooting information PI is information (image quality generation information) related to the image quality when the image data is generated (taken) in the image data generation device such as the digital still camera 12, and is automatically recorded with shooting. Parameters relating to exposure time, ISO sensitivity, aperture, shutter speed, focal length, and exposure correction amount, light source, shooting mode, and the like arbitrarily set by the user.

  Detailed attached information stored in the Exif IFD will be described with reference to FIG. FIG. 5 is an explanatory diagram showing an example of detailed attached information stored in the Exif IFD of the image file GF that can be used in this embodiment.

The Exif IFD stores Exif version information, color space information, image data generation date and time, and shooting condition tags. In the tag relating to the shooting condition (shooting information IP), parameter values such as exposure time, lens F value, exposure control mode, ISO sensitivity, exposure correction amount, light source, white balance, flash, focal length, and the like are stored according to predetermined offsets. Has been. On the image processing device (output device) side, desired photographing information PI can be acquired by designating an offset corresponding to desired tag information (parameter).
C. Image processing in the color printer 20:

  Hereinafter, image processing executed by the color printer 20 will be described with reference to FIGS. FIG. 6 is a flowchart showing a processing routine of image processing in the image processing apparatus (color printer 20) according to the present embodiment. FIG. 7 is a flowchart showing a processing routine of image quality adjustment processing (automatic image quality adjustment processing) using a reference value in the image processing apparatus (color printer 20) according to the present embodiment. FIG. 8 is an explanatory diagram showing the brightness correction amount according to the conventional method and the brightness correction amount according to the method according to the present embodiment in comparison.

  When the memory card MC is inserted into the slot 22, the control circuit 23 (CPU 231) of the color printer 20 reads the image file GF from the memory card MC, and temporarily stores the read image file GF in the RAM 233 (step S100). . The CPU 231 expands the image data GD included in the read image file GF, performs a matrix operation using the matrix S on the expanded image data GD, and executes a YCbCr → RGB color conversion process (step S110).

  As described above, the image file GF in this embodiment stores image data in the JPEG file format as the image data GD, and the image data in the JPEG file format is data obtained by compressing YCbCr data. Also, RGB data is generally used in image processing in current personal computer PCs and printers. Therefore, decompression (decoding) of JPEG file format image data and color conversion processing of YCbCr data to RGB data are required. The matrix S is a matrix generally used when converting YCbCr data to RGB data in the JFIF format that defines the specifications for JPEG files, and is a matrix well known to those skilled in the art. Is omitted.

  The CPU 231 executes image quality adjustment processing using the reference value for the RGB data obtained by the conversion (step S120). The image quality adjustment process using the reference value is generally an image process called automatic image quality adjustment process, and is a preferable standard parameter stored in the ROM 232 in advance without depending on an external input. This is a process of adjusting the image quality using the value (reference value). The parameters used in such image quality adjustment are, for example, parameters relating to image quality such as brightness and sharpness. A correction amount to be corrected is obtained by using standard parameter values for these parameters, and the obtained correction amount is applied. Adjust the image quality. Details will be described later with reference to FIG.

  The CPU 231 executes color conversion processing for converting image data (RGB data) that has been subjected to automatic image quality adjustment processing into CMYK data (step S130). That is, the color system of the image data is converted into the CMYK color system which is the color system used when the color printer 20 executes the printing process. Specifically, it is executed using a lookup table in which the RGB color system stored in the ROM 232 is associated with the CMYK color system.

  After completing the above image processing, the CPU 231 executes print output processing using the obtained image data (step S140), and ends this processing routine. In the print output process, the CPU 231 executes halftone process and resolution conversion process, and sends the processed data to the printing unit 21 as raster data.

The automatic image quality adjustment process will be described in detail with reference to FIG. The CPU 231 executes image data analysis (step S200). That is, in the automatic image quality adjustment processing in the present embodiment, various characteristic parameter values indicating the characteristics of the image data GD by analyzing the image data GD in units of pixels, for example, the minimum luminance value, the maximum luminance value, the brightness representative value, etc. Get image statistics. At this time, since the image data GD is RGB data, the minimum luminance value Ymin, the maximum luminance value Ymax, and the like are obtained using the equation Y = 0.30R + 0.59G + 0.11B.
The CPU 231 performs level correction (contrast correction) using the minimum luminance value Ymin and the maximum luminance value Ymax (step S210). Specifically, if the RGB components of the original image data GD are R, G, B and the corrected RGB components are R ′, G ′, B ′, (R ′, G ′, B ′) = 255 * Correction is performed on each pixel using the equation (R, G, B) (Ymax−Ymin) −Ymin. The CPU 231 calculates a luminance difference ΔY = Ymod−Yorg between the luminance value at 128 points of the original image data (image data before level correction) and the luminance value Ymod at 128 points of the corrected image data (step S220). Note that 128 points is one of the horizontal axis (input value) points in the tone curve, where the horizontal axis represents the input value of the image data (original image data) and the vertical axis represents the output value of the image data (corrected image data). One. In this embodiment, level correction is executed after conversion to RGB data. However, these processes may be executed using the luminance component Y at the stage of YCbCr data.

  The CPU 231 calculates the original lightness correction amount (lightness correction amount not considering the exposure correction amount) tCurve_Yorg using Equation 1 below (step S230).

  For example, when the lightness reference value Bref = 128 and the lightness representative value Bsmp = 56 obtained by sampling (analysis), tCurve_Yorg = 16 (see FIG. 8). The brightness reference value Bref is, for example, 8-bit information that can take a value of 0 to 255, and is set to 128 in this embodiment.

  The CPU 231 determines whether or not shooting information PI (Exif IFD) is included in the image data GF (step S240). If the CPU 231 determines that shooting information PI is included (step S240: Yes), A corrected brightness correction amount tCurve_Y considering the exposure correction amount (exposure amount) EV is calculated (step S250). The corrected brightness correction amount tCurve_Y is calculated using the following Equation 2.

  Here, the luminance difference ΔY is a correction term for compensating for the influence on the brightness of the image data GD caused by the contrast (level) correction. If the signs of the luminance difference ΔY and the exposure correction amount EV are different, the corrected brightness correction amount tCurve_Y is calculated with the luminance difference ΔY = 0. In such a case, since the photographer's intention regarding exposure and the direction of automatic correction are contradictory, the compensation value resulting from contrast correction is not applied in order to prioritize the photographer's intention.

  The CPU 231 applies the obtained corrected brightness correction amount tCurve_Y to the tone curve, executes image quality adjustment including brightness (step S260), and ends this processing routine. That is, the characteristic of the tone curve is corrected using the corrected brightness correction amount tCurve_Y, and the output values (output levels) of the R, G, and B components of the image data GD are corrected for each pixel using the corrected tone curve. (change.

  If the CPU 231 determines that the shooting information PI is not included (step S240: No), the exposure correction amount (exposure amount) EV cannot be taken into account, and the original brightness correction amount tCurve_Yorg is used as the tone curve. The image quality adjustment including brightness is applied to execute (step S270), and this processing routine is ended.

  For example, the correction of the tone curve characteristics using the corrected brightness correction amount tCurve_Y or the original brightness correction amount tCurve_Yorg is performed as shown in FIG. FIG. 9 is an explanatory diagram showing an example of tone curve correction in brightness correction. When the exposure correction amount EV is a positive value, that is, when the photographer wants to make the brightness brighter, for example, the output level OL1, corresponding to the lightness correction amount at a quarter of the input level. Lift OL2. On the other hand, when the exposure correction amount is a negative value, that is, when the photographer wants correction to darken the brightness, the output level OL3 is set according to the correction level at, for example, 3/4 of the input level. Lower. Values other than the points corresponding to the correction level are interpolated with a spline curve.

  FIG. 8 shows a comparison between the brightness correction amount obtained by the color printer 20 according to this embodiment and the brightness correction amount according to the conventional method. Here, the lightness correction by the conventional method is a method of obtaining the lightness correction amount by changing the lightness reference value Bref in accordance with the exposure correction amount EV in the above formula 1. For example, when the standard value of the lightness reference value Bref is 128, a value calculated using a conversion formula of 0.1 EV = 2 (lightness correction value) with respect to this standard value is obtained with respect to the lightness standard value 128. The brightness reference value Bref is corrected by adding. That is, Bref = standard value + (2 * exposure correction amount EV / 0.1). When the exposure correction amount EV is positive, the brightness correction value is added to the standard value, and when the exposure correction amount EV is negative. The brightness correction value is subtracted from the standard value.

  For example, when the brightness representative value Bsmp = 56 and the exposure correction amount EV = −1.0, the brightness reference value Bref is corrected from 128 to 108, and the brightness correction amount calculated using the corrected brightness reference value. Becomes 14. When the brightness representative value Bsmp = 56 and the exposure correction amount EV = −2.0, the brightness reference value Bref is corrected from 128 to 88, and the brightness correction amount calculated using the corrected brightness reference value. Becomes 11.

  On the other hand, according to the color printer 20 according to the present embodiment, when the luminance difference ΔY = + 5, the lightness representative value Bsmp = 56, and the exposure correction amount EV = −1.0, the respective values are applied to Equation 2. , Corrected brightness correction amount = 8. Further, when the luminance difference ΔY = + 5, the lightness representative value Bsmp = 56, and the exposure correction amount EV = −2.0, applying the respective values to Equation 2, the corrected lightness correction amount tCurve_Y = 4.

  Therefore, according to the color printer 20 (image processing apparatus) according to the present embodiment, the brightness of the image data GD can be automatically adjusted to reflect the shooting information PI included in the image file GF. Therefore, when the image output tendency is arbitrarily set by the user, the image quality adjustment by the automatic image quality adjustment process is suppressed, so that the automatic image quality adjustment process reflecting the user's intention can be executed.

  In particular, according to the color printer 20 of the present embodiment, the lightness correction amount is corrected by reducing the lightness correction amount not considering the exposure correction amount EV by 2 | EV |, so that the lightness correction amount is corrected by a conventional method. As compared with the above, it is possible to execute brightness correction more in accordance with the photographer's intention. That is, as the absolute value of the exposure correction amount increases, the corrected brightness correction amount tCurve_Y can be significantly reduced geometrically (exponentially). Therefore, the photographer's intention to make the output result brighter or darker can be more accurately reflected in the output result of the image data.

  Furthermore, according to the color printer 20 in the present embodiment, the brightness correction amount is corrected (corrected) in consideration of the luminance difference ΔY before and after the contrast correction (level correction). Can be compensated. Therefore, even when contrast correction is executed, it is possible to execute brightness correction that matches the photographer's intention.

In addition, since the image quality can be automatically adjusted using the shooting information PI included in the image file GF, the user can easily capture the image without adjusting the image quality on the photo retouching application or the printer driver. Reflected high-quality printing results can be obtained.
Other examples:

  In the image processing in the above embodiment, the image quality adjustment processing using the reference value is executed after the YCbCr-RGB color conversion processing, but further image processing may be added as shown in FIG. FIG. 10 is a flowchart showing a processing routine of image processing added in another embodiment. Since the steps before the YCbCr-RGB color conversion process (step S110) and the steps after the image quality adjustment process using the reference value (step S120) have been described, the description thereof will be omitted.

  Prior to the subsequent color conversion process, the CPU 231 performs gamma correction on the image data converted into RGB data in order to linearize the image data (step S111). The gamma value used in the gamma correction is a gamma value unique to the digital still camera, and may be acquired based on the parameters of the shooting information PI, or an image associated with the image data GD separately from the shooting information PI. It may be provided as processing information.

  The CPU 231 executes a color conversion process for converting RGB data into wRGB data using a matrix (step S112). Here, the wRGB color space is preferably a color space having a wide area including at least a part of the sRGB color space, as compared with a generally used sRGB color space. By using such a wide RGB color space, it is possible to connect to the subsequent automatic image quality adjustment processing without losing the value of the RGB data converted from the YCbCr data. The matrix used at this time is a matrix for converting RGB data to XYZ data, for example, a matrix M, a matrix for converting wRGB data to XYZ data, for example, a composite matrix N-1M of matrix N, or matrix M and Matrix N-1.

  The CPU 231 performs inverse gamma correction on the image data converted into wRGB data (step S113). The gamma value used for the inverse gamma correction is a gamma value unique to the color printer 20 and is stored in advance in the ROM 232, for example. By executing such inverse gamma correction, it is possible to generate image data GD in consideration of the gamma characteristics of the color printer 20.

  The CPU 231 sequentially executes the above-described automatic image quality adjustment processing (step S120) and subsequent steps. According to the present embodiment, since the automatic image quality adjustment process can be executed without losing the value of the RGB data converted from the YCbCr data, a more appropriate image quality adjustment process can be executed.

  In the above-described embodiment, an example in which brightness image quality adjustment processing is automatically performed based on a single reference value has been described. However, a tendency of brightness correction on the operation panel of the color printer 20, for example, brightness or darkening. The image quality automatic adjustment button may be provided, and the lightness reference value Bref and the lightness correction amount may be changed according to the lightness correction tendency selected by the automatic image quality adjustment button.

  In the above embodiment, an example in which image quality adjustment processing is automatically executed has been described. However, an image quality automatic adjustment button is provided on the operation panel of the color printer 20, and image quality automatic adjustment selected by the image quality automatic adjustment button is performed. The image quality automatic adjustment process of the above embodiment may be executed only when it is selected.

  In the above embodiment, all image processing is executed in the color printer 20 without using the personal computer PC, and a dot pattern is formed on the print medium according to the generated image data GD. Or you may make it run a part on a computer. In this case, the image data processing application such as a retouch application or a printer driver installed in a hard disk of a computer is provided with the image processing function described with reference to FIGS. The image file GF generated by the digital still camera 12 is provided to the computer via a cable or a memory card MC. On the computer, an application is started by a user operation, and reading of the image file GF, analysis of the shooting information PI, conversion and adjustment of the image data GD are executed. Alternatively, the application is automatically started by detecting the insertion of the memory card MC or by detecting the insertion of the cable, reading the image file GF, analyzing the shooting information PI, and image data GD. Conversion and adjustment may be automatically performed.

  Further, all or part of the image processing executed by the personal computer PC may be executed by the digital still camera 12. In this case, the image data processing application such as a retouch application or a printer driver stored in the ROM or the like of the digital still camera 12 is provided with the image processing function described with reference to FIGS. . Printing data including a printing control command and printing image data generated by the digital still camera 12 is provided to the printer 20 via a cable or a memory card MC. The printer 20 that has received the print data forms a dot pattern on the print medium according to the print image data and outputs an image. The digital still camera 12 may provide printing image data (image processed image data) to the personal computer PC or the printer 20. In such a case, a print control command is given to the print image data in the personal computer PC or the printer 20.

  In the above embodiment, the automatic image quality adjustment has been described focusing on the lightness correction in consideration of the exposure correction amount, but other examples include, for example, shadow / contrast point, contrast, color balance, saturation, The automatic adjustment of the image quality reflecting the photographing information PI can be executed on the characteristic parameter values of the image data GD such as the sharpness.

  Furthermore, a characteristic parameter value for executing automatic image quality adjustment may be selected. For example, the color printer 20 may be provided with a parameter selection button or a shooting mode parameter selection button in which predetermined parameters are combined according to the subject, and parameters for executing automatic image quality adjustment may be selected with these selection buttons. When automatic image quality adjustment is executed on a personal computer, a parameter for executing automatic image quality adjustment may be selected on a user interface of a printer driver or a retouch application.

  In the above embodiment, the lightness correction amount is reduced geometrically as the exposure correction amount increases, but the degree of change in the lightness correction amount with respect to the exposure correction amount less than the predetermined exposure correction amount and the predetermined exposure The degree of change of the brightness correction amount with respect to the exposure correction amount equal to or greater than the correction amount may be made different. Alternatively, the reduction rate of the brightness correction amount may be decreased as the exposure correction amount increases. Even in such a case, it is possible to maintain the gradation of the highlight or shadow portion even when the exposure correction amount is large, and as a result, it is possible to prevent the occurrence of whiteout or blackout.

  In the above-described embodiments, the color printer 20 is used as an output device. However, a display device such as a CRT, LCD, or projector can be used as the output device. In such a case, an image processing program (display driver) that executes the image processing described with reference to FIGS. 6 to 8 is executed by the display device as the output device, for example. Alternatively, when a CRT or the like functions as a computer display device, an image processing program is executed on the computer side. However, finally output image data has an RGB color space instead of a CMYK color space.

  In such a case, the shooting information PI at the time of image data generation is reflected in the display result on a display device such as a CRT in the same manner that the information at the time of image data generation can be reflected in the print result via the color printer 20. be able to. Therefore, the image data GD generated by the digital still camera 12 can be displayed more accurately.

  In the above embodiment, an Exif format file has been described as a specific example of the image file GF, but the format of the image file according to the present invention is not limited to this. That is, any image file including image data GD and information relating to exposure correction associated with the image data GD may be used. Further, the information related to exposure correction may be image data shooting information PI or image processing control information for more actively controlling the image processing apparatus. The parameters stored as the shooting information PI shown in FIG. 8 used in the above embodiment are merely examples, and various parameters according to the Exif standard can be stored.

  The digital still camera 12 and the color printer 20 used in the above-described embodiments are merely examples, and the configuration is not limited to the description of each embodiment. The digital still camera 12 only needs to have at least a function capable of generating the image file GF according to the above embodiment. Further, in the color printer 20, at least the shooting information PI of the image file GF according to the present embodiment is analyzed, and the image quality is automatically adjusted to reflect the user's intention regarding the brightness, and the image is output (printed). I can do it.

  In the above embodiment, the case where the image data GD and the shooting information PI are included in the same image file GF has been described as an example. However, the image data GD and the shooting information PI need not necessarily be stored in the same file. There is no. That is, image data GD and shooting information PI (image processing control information) need only be associated. For example, association data that associates image data GD and shooting information PI (image processing control information) is generated, or 1 or A plurality of image data GD and shooting information PI may be stored in independent files, and the shooting information PI associated with processing the image data GD may be referred to. In such a case, at the time of image processing using the shooting information PI, the image data and the shooting information PI are inseparable and function in the same manner as when stored in the same file. It is. Furthermore, a moving image file stored in an optical disc medium such as a CD-ROM, a CD-R, a DVD-ROM, a DVD-RAM is also included.

  As described above, the image processing apparatus according to the present invention has been described based on some embodiments. However, the above-described embodiments of the present invention are intended to facilitate understanding of the present invention and limit the present invention. It is not a thing. The present invention can be changed and improved without departing from the spirit and scope of the claims, and it is needless to say that the present invention includes equivalents thereof.

It is explanatory drawing which shows an example of the image processing system which can apply the image processing apparatus which concerns on a present Example. 1 is a block diagram illustrating a schematic configuration of a digital still camera capable of generating image data to be processed by an image processing apparatus according to an embodiment. 1 is a block diagram illustrating a schematic configuration of a color printer that functions as an image processing apparatus according to an embodiment. It is explanatory drawing which shows the schematic internal structure of the image file GF according to an Exif format. It is explanatory drawing which shows an example of the detailed attached information stored in Exif IFD of the image file GF which can be used for a present Example. 4 is a flowchart illustrating a processing routine of image processing in the color printer 20 according to the present embodiment. 4 is a flowchart showing a processing routine of automatic image quality adjustment processing using a reference value in the image processing apparatus (color printer 20) according to the present embodiment. It is explanatory drawing which shows the brightness correction amount by a conventional method, and the brightness correction amount by the method which concerns on a present Example by contrasting. It is explanatory drawing which shows an example of the correction of the tone curve in brightness correction. It is a flowchart which shows the process routine of the image process added in another Example.

Claims (29)

An image processing apparatus that performs image processing on image data using image data and an exposure correction amount for the image data,
A correction amount determination unit that determines a lightness correction amount of the image data using a lightness reference value that is a reference for image quality adjustment relating to lightness;
A correction amount correction unit that decreases the lightness correction amount as the exposure correction amount increases;
An image processing apparatus comprising: an image quality adjustment unit that adjusts the brightness of the image data by applying the corrected brightness correction amount. The image processing apparatus according to claim 1.
The correction amount correction unit includes a degree of change in the lightness correction amount with respect to the exposure correction amount less than a predetermined exposure correction amount, and a degree of change in the lightness correction amount with respect to the exposure correction amount greater than or equal to the predetermined exposure correction amount. Is an image processing device. The image processing apparatus according to claim 1.
The correction amount correction unit is an image processing apparatus that reduces a reduction rate of the brightness correction amount as the exposure correction amount increases. The image processing apparatus according to claim 2,
The correction amount correction unit is an image processing apparatus that reduces the lightness correction amount geometrically as the exposure correction amount increases. The image processing apparatus according to claim 4.
The correction amount correction unit is an image processing device that divides the brightness correction amount by an exponential function using the exposure correction amount as a parameter. The image processing apparatus according to claim 5 further includes:
A lightness characteristic value acquisition unit that analyzes the image data and acquires a lightness characteristic value indicating characteristics relating to the lightness of the image data;
The image processing apparatus, wherein the correction amount determination unit determines the lightness correction amount so as to reduce a deviation between the lightness reference value and the acquired lightness characteristic value. The image processing apparatus according to claim 5 further includes:
An input unit for inputting a tendency of brightness correction for the image data;
The correction amount determination unit is an image processing apparatus that determines a lightness correction amount of the image data based on the input lightness correction tendency. The image processing apparatus according to claim 6 further includes:
An image processing apparatus comprising an image output unit that outputs an image using the image data having the brightness adjusted. The image processing apparatus according to any one of claims 1 to 8,
The correction amount correction unit corrects the brightness correction amount in consideration of a luminance difference before and after contrast correction,
The image processing apparatus in which the image data and the exposure correction amount are stored in the same file. An image processing apparatus that performs image processing on image data using image data and information on exposure correction performed on the image data,
A lightness characteristic value acquisition unit that analyzes the image data and acquires a lightness characteristic value indicating characteristics relating to the lightness of the image data;
An image quality adjustment unit for reducing a deviation between a brightness reference value serving as a reference for image quality adjustment relating to brightness and the acquired brightness characteristic value;
An image processing apparatus comprising: a deviation reduction amount adjusting unit that reduces the degree of reduction of the deviation as the degree of exposure correction performed on the image data increases based on the exposure correction information. The image processing apparatus according to claim 10.
The correction amount correction unit includes a degree of change in the lightness correction amount with respect to the exposure correction amount less than a predetermined exposure correction amount, and a degree of change in the lightness correction amount with respect to the exposure correction amount greater than or equal to the predetermined exposure correction amount. Is an image processing device. The image processing apparatus according to claim 10.
The correction amount correction unit is an image processing apparatus that reduces a reduction rate of the brightness correction amount as the exposure correction amount increases. The image processing apparatus according to claim 12.
The degree of the reduction of the deviation is an image processing apparatus in which the deviation reduction amount adjustment unit reduces the degree of geometric progression. The image processing apparatus according to any one of claims 10 to 13,
The image processing apparatus in which the image data and the exposure correction information are stored in the same file. An image processing method for image data using image data and an exposure correction amount for the image data,
Determining a lightness correction amount of the image data using a lightness reference value serving as a reference for image quality adjustment relating to lightness;
As the exposure correction amount increases, the brightness correction amount is corrected to be small,
An image processing method for adjusting the brightness of the image data by applying the corrected brightness correction amount. The image processing method according to claim 15, wherein
In the correction of the lightness correction amount, the degree of change in the lightness correction amount with respect to the exposure correction amount less than a predetermined exposure correction amount, and the change in the lightness correction amount with respect to the exposure correction amount greater than or equal to the predetermined exposure correction amount. Image processing method with different degree of. The image processing method according to claim 15, wherein
The lightness correction amount is an image processing method in which a reduction rate is reduced as the exposure correction amount is increased. The image processing method according to claim 17,
The image processing method, wherein the lightness correction amount is corrected to be a geometric series smaller. The image processing method according to claim 15 further includes:
Analyzing the image data, obtaining a lightness characteristic value indicating characteristics relating to the lightness of the image data,
Determining the brightness correction amount so as to reduce a deviation between the brightness reference value and the acquired brightness characteristic value;
An image processing method for dividing the determined brightness correction amount by an exponential function using the exposure correction amount as a parameter. The image processing method according to claim 15 further includes:
Receiving a tendency of brightness correction for the image data;
Based on the received lightness correction tendency, determine a lightness correction amount of the image data,
An image processing method for dividing the determined brightness correction amount by an exponential function using the exposure correction amount as a parameter. A computer-readable recording medium that records an image processing program for performing image processing on image data using image data and an exposure correction amount for the image data, the image processing program comprising:
A function for determining a lightness correction amount of the image data using a lightness reference value serving as a reference for image quality adjustment relating to lightness;
A function of correcting the brightness correction amount to be smaller as the exposure correction amount is increased;
A computer-readable recording medium that causes a computer to execute a function of adjusting the brightness of the image data by applying the corrected brightness correction amount. The computer-readable recording medium according to claim 21,
The function of correcting the lightness correction amount includes the degree of change in the lightness correction amount with respect to the exposure correction amount less than a predetermined exposure correction amount and the lightness correction amount with respect to the exposure correction amount greater than or equal to the predetermined exposure correction amount. A computer-readable recording medium that has a function of varying the degree of change. The computer-readable recording medium according to claim 21,
The brightness correction amount is a computer-readable recording medium in which a reduction rate is reduced as the exposure correction amount is increased. The computer-readable recording medium according to claim 23,
The brightness correction amount is a computer-readable recording medium that is made geometrically smaller. The computer-readable recording medium according to claim 21, further comprising:
A function of analyzing the image data and obtaining a brightness characteristic value indicating characteristics relating to the brightness of the image data is realized by a computer,
The function of determining the correction amount determines the lightness correction amount so as to reduce a deviation between the lightness reference value and the acquired lightness characteristic value,
The function of correcting the brightness correction amount is a computer-readable recording medium that divides the determined brightness correction amount by an exponential function using the exposure correction amount as a parameter. The computer-readable recording medium according to claim 21, further comprising:
A function for inputting a tendency of brightness correction for the image data is realized by a computer,
The function of determining the correction amount determines a lightness correction amount of the image data based on the input lightness correction tendency,
The function of correcting the brightness correction amount is a computer-readable recording medium that divides the determined brightness correction amount by an exponential function using the exposure correction amount as a parameter. A computer-readable recording medium according to any one of claims 21 to 26 is further provided.
A computer-readable recording medium that causes a computer to realize a function of outputting the image data with adjusted brightness to an output device. An image processing apparatus that executes image processing on image data associated with shooting information indicating shooting conditions at the time of shooting,
An image quality characteristic value acquisition unit that analyzes the acquired image data and acquires an image quality characteristic value indicating the image quality characteristic of the image data;
A search unit for searching for shooting information indicating a shooting intention from the shooting information associated with the acquired image data;
An image quality adjustment unit that adjusts the image quality of the image data by reducing a deviation between an image quality adjustment reference value serving as a predetermined image quality adjustment reference and the acquired image quality characteristic value;
An image processing comprising: a deviation reduction amount adjustment unit that adjusts a degree of reduction of the deviation by using the searched shooting information indicating the shooting intention when the shooting information indicating the shooting intention can be detected. apparatus. The image processing apparatus according to claim 28, wherein
An image processing apparatus in which the degree of reduction of the deviation is not adjusted depending on the shooting information indicating the shooting intention when the shooting information indicating the shooting intention cannot be detected.

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