JP2011130437A - Image processing apparatus and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus which properly corrects a difference in color reproduction ranges between input and output devices. <P>SOLUTION: An image processing apparatus comprises a control means and a correction means. Based on an output color reproduction range of an image output device that outputs an image based on input image data and a color reproduction distribution of pixels of the input image data, the control means controls an image correction parameter for correcting each of out-of-range pixels located outside the output color reproduction range among the pixels of the input image data. Based on the image correction parameter controlled by the control means, the correction means corrects the input image data. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  Embodiments described herein relate generally to an image processing apparatus and an image processing method.

  Various techniques for automatically correcting images taken with a digital camera or the like have been proposed. For example, a technique has been proposed in which a histogram is created from bitmap data corresponding to a captured image, a feature amount is extracted from the created histogram, and the image is corrected based on the feature amount.

JP 2002-232728 A

  However, due to the difference in the color reproduction range between input / output devices, that is, the difference in gamut, when the image is output by an output device such as a display or a multifunction printer (MFP), the saturation or gradation of the image is reduced. May fall. This is because the correction amount for dealing with the difference in gamut between the input / output devices is insufficient or excessive.

  An object of the present invention is to provide an image processing apparatus and an image processing method excellent in correction to cope with a difference in color reproduction range between input / output devices.

  According to the embodiment, the image processing apparatus includes a control unit and a correction unit. The control means is configured to output the output of each pixel of the input image data based on an output color reproduction range of an image output device that outputs an image based on the input image data and a color reproduction distribution of each pixel of the input image data. An image correction parameter for correcting each out-of-range pixel out of the color reproduction range is controlled. The correction unit corrects the input image data based on the image correction parameter controlled by the control unit.

It is sectional drawing which shows an example of a hardware structure of the image processing apparatus which concerns on embodiment. It is a block diagram which shows an example of a structure of each function of the image processing apparatus which concerns on embodiment. 6 is a flowchart illustrating an example of a printing process performed by the image processing apparatus. It is a flowchart which shows an example of an image correction process. It is a flowchart which shows an example of a gamut difference calculation process. It is a figure for demonstrating the distance calculation of an output gamut boundary surface and an attention pixel. It is a figure which shows an example of the gamut plot after a correction process and before a gamut mapping process. It is a figure which shows an example of the gamut plot after a correction process and after a gamut mapping process. It is a figure which shows an example of the gamut plot before the gamut mapping process at the time of correction processing non-application. It is a figure which shows an example of the gamut plot after a gamut mapping process at the time of correction processing non-application.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating an example of a hardware configuration of an image processing apparatus according to the embodiment. FIG. 2 is a block diagram illustrating an example of a configuration of each function of the image processing apparatus according to the embodiment.

  The image processing apparatus shown in FIGS. 1 and 2 is, for example, a multifunction printer (MFP). As shown in FIGS. 1 and 2, the image processing apparatus includes an external information input unit 11, a paper storage unit 12, and a printing unit 13. Further, as illustrated in FIG. 2, the image processing apparatus includes a control unit 20, and the control unit 20 includes a CPU 21, a storage device 22, and an arithmetic I / O unit 23.

  The external information input unit 11 receives a print job command, a bitmap image, and input image gamut information transmitted from, for example, a personal computer via a network.

  The arithmetic I / O unit 23 receives the print job command, the bitmap image, and input image gamut information (information on the input color reproduction range). The CPU 21 stores the print job command, the bitmap image, and the input image gamut information in the storage device 22. The arithmetic I / O unit 23 also receives output image gamut information (information relating to the output color reproduction range) transmitted from the printing unit 13. The CPU 21 stores the output image gamut information in the storage device 22. Alternatively, in response to the initial setting, the storage device 22 stores the output image gamut information of the printing unit 13.

  The input image gamut information is, for example, gamut data on the display of the personal computer. That is, it is the gamut data (data relating to the color reproduction range of the display) of the display that displayed the image based on the bitmap image. The output image gamut information is gamut data of the printing unit 13 (data related to the color reproduction range of the printing unit 13).

  FIG. 3 is a flowchart illustrating an example of a printing process performed by the image processing apparatus. As shown in FIG. 3, the image processing apparatus receives a print job command, a bitmap image, and input image gamut information transmitted from, for example, a personal computer via a network (ACT1). The control unit 20 (CPU 21) applies an image correction process to be described later to the bitmap image (ACT2), and further performs a gamut mapping process (color compression process) on the bitmap image to which the image correction process is applied. Execute (ACT3). Further, the control unit 20 (CPU 21) controls the conveyance of the paper stored in the paper storage unit 12 (ACT4). In response to this, the paper storage unit 12 picks up and conveys the paper. The printing unit 13 forms an image based on the bitmap image subjected to the gamut mapping process on the conveyed paper (ACT5), and carries out the paper on which the image is formed (ACT6).

  FIG. 4 is a flowchart illustrating an example of the image correction process described above. As shown in FIG. 4, the control unit 20 (CPU 21) calculates a correction feature amount for image quality correction based on the bitmap image stored in the storage device 22 (ACT 21). For example, the control unit 20 (CPU 21) calculates the local average brightness as the correction feature amount. That is, the control unit 20 (CPU 21) converts the bitmap image into a YCbCr image, and calculates the average value (local average brightness) by adding the luminance values in the rectangular area of the Y component image of the YCbCr image.

  As described above, the control unit 20 (CPU 21) calculates a correction feature amount and then calculates a gamut difference (ACT 22). For example, the control unit 20 (CPU 21) counts the number of out-of-range pixels out of the output gamut (output color reproduction range) indicated by the output image gamut information among the pixels constituting the bitmap image, and according to the count result Calculate the gamut difference. Alternatively, the control unit 20 (CPU 21) calculates the gamut difference based on the distance between the output gamut boundary (boundary of the output color reproduction range) indicated by the output image gamut information and the pixels outside each range. For example, the control unit 20 (CPU 21) calculates a gamut difference corresponding to the sum of the distances between the output gamut boundary indicated by the output image gamut information and the pixels outside the range.

  The control unit 20 (CPU 21) executes image correction processing based on the gamut difference (ACT 23). As will be described in detail later, the control unit 20 (CPU 21) variably controls the image correction parameter based on the gamut difference, and executes image correction processing based on the variably controlled image correction parameter. For example, the image correction parameter is a parameter for controlling the strength of image correction processing. Therefore, the control unit 20 can control the strength of the image correction process according to the gamut difference.

  Hereinafter, description will be given focusing on the calculation of the gamut difference based on the distance between the boundary of the output color reproduction range and the pixels outside each range.

  FIG. 5 is a flowchart illustrating an example of a gamut difference calculation process. As shown in FIG. 5, the control unit 20 (CPU 21) converts the input image into Lab (ACT 221). Subsequently, the control unit 20 (CPU 21) determines whether the pixel of interest among the plurality of pixels constituting the input image is inside or outside the output gamut (output gamut boundary) (ACT 222). When the target pixel is located outside the output gamut (output gamut boundary) (ACT 222, YES), as shown in FIG. The calculated distance value is added to the gamut difference (ACT 223). The control unit 20 (CPU 21) executes the above process for all the pixels constituting the input image, and calculates the gamut difference (ACT 221 to ACT 224).

  In summary, the control unit 20 (CPU 21) is out of each range out of the output gamut (output gamut boundary) out of each pixel constituting the input image based on the output gamut and the color reproduction distribution of each pixel constituting the input image. The situation (distribution) of the pixels is detected, and a gamut difference is calculated based on the situation (distribution) of each out-of-range pixel. In other words, the control unit 20 (CPU 21) detects a situation (distribution) of how much each out-of-range pixel is out of the output gamut, and calculates a gamut difference based on the situation of each out-of-range pixel.

  As described above, the control unit 20 (CPU 21) executes image correction processing based on the calculated gamut difference (ACT 23). For example, the control unit 20 (CPU 21) variably controls the local brightness correction parameter based on the calculated gamut difference, and executes the local brightness correction process based on the variably controlled local brightness correction parameter. That is, the control unit 20 (CPU 21) controls the strength of the local brightness correction process based on the calculated gamut difference, and executes the local brightness correction process.

The following equation [Equation 1] shows an example of local brightness correction processing.

  For example, when the gamut difference is large, the input image is corrected by increasing the color compression amount for the input image. Thus, the corrected image becomes an image corresponding to the output gamut of the output device, and the corrected image can be output by the output device. That is, each pixel constituting the corrected image is within the output gamut. However, if the color compression amount for the input image is simply increased simply because the gamut difference is large, gradation collapse tends to occur.

Therefore, when the gamut difference is large, the control unit 20 (CPU 21) corrects the image more strongly before color compression (for example, local brightness correction) so that the gradation is maintained even after color compression. As described above, the control unit 20 (CPU 21) can adjust the image correction processing (correction amount) according to the gamut difference. For example, the control unit 20 (CPU 21) executes the local brightness correction process based on the following formula [Equation 2].

  In the above [Equation 2], the case where the gamut difference and the adjustment amount are linear is shown, but it may be nonlinear. As described above, the control unit 20 (CPU 21) executes the correction process (local brightness correction process) based on the above equation [Equation 2].

  Further, the control unit 20 (CPU 21) executes gamut mapping (color compression processing) after the correction processing based on the above equation [Equation 2]. FIG. 7 is a diagram illustrating an example of a gamut plot after the correction process based on the above equation [Formula 2] and before the gamut mapping process. FIG. 8 is a diagram illustrating an example of a gamut plot after the correction processing based on the above equation [Formula 2] and after the gamut mapping processing.

  On the other hand, FIG. 9 is a diagram illustrating an example of a gamut plot before the gamut mapping process in the case where the correction process based on the above equation [Equation 2] is not applied. FIG. 10 is a diagram illustrating an example of a gamut plot after the gamut mapping process in the case where the correction process based on the above equation [Formula 2] is not applied.

  In FIG. 10, the gradation of the pixel A and the pixel B plotted on the ab plane in the Lab space is crushed (while the distance between the pixel A and the pixel B is greatly reduced). FIG. 8 shows that the gradation of the pixel A and the pixel B plotted on the ab plane in the Lab space is maintained (the distance between the pixel A and the pixel B is not reduced so much).

  The control unit 20 (CPU 21) corrects the input image based on the above equation [Equation 2], then executes gamut mapping processing on the corrected image, and further controls image formation based on the gamut mapping processing image. In response to this, the paper storage unit 12 picks up and conveys the paper, and the printing unit 13 forms an image on the conveyed paper based on the gamut mapping processing image.

  The present embodiment will be summarized below.

  The image processing apparatus of the present embodiment outputs (displays or prints) bitmap data acquired by an image input apparatus such as a scanner or a digital camera. The image processing device performs image correction on the input image (bitmap data) transmitted from the image input device in order to improve the appearance of the image. At this time, the image processing apparatus controls the strength of image correction according to the characteristics of the bitmap data and the engine characteristics (particularly the color reproduction range). For example, the image processing apparatus (control unit 20) controls the intensity of the image correction based on the color reproduction distribution and engine characteristics (particularly the color reproduction range) of each pixel constituting the bitmap data. That is, the image processing apparatus (control unit 20) detects the situation of each out-of-range pixel out of the color reproduction range which is an engine characteristic among the respective pixels constituting the input image, and determines which out-of-range pixel is out of the color reproduction range The image correction parameter is variably controlled based on whether the image is deviated from the image, and the image is corrected (for example, local brightness correction) based on the variably controlled image correction parameter. That is, the image processing apparatus (control unit 20) can control the strength of image correction (for example, local brightness correction) based on the variably controlled image correction parameter.

  In particular, correction processing that improves contrast (such as local brightness correction and contrast correction) may cause blackout between input / output devices with different color reproduction ranges. At this time, if correction is performed without considering engine characteristics, there is a possibility that blackout may be promoted. As described above, the image processing apparatus according to the present embodiment controls the intensity of image correction (for example, local brightness correction) based on the characteristics of bitmap data and the engine characteristics, and thus can reduce such blackout. .

  For example, as described above, the image processing apparatus (control unit 20) variably controls the image correction parameter based on the sum of the distances between the boundaries of the output color reproduction range and the pixels outside the range. As a specific example, the image processing apparatus (control unit 20) sets the first image correction parameter based on the first total value (relatively low value), and the second total sum larger than the first total value. A second image correction parameter is set based on the value (relatively high value). Further, the image processing apparatus (control unit 20) converts the first brightness difference between the first and second out-of-range pixels to a second brightness difference wider than the first brightness difference based on the first image correction parameter. After that, the input image corrected by the first image correction parameter is subjected to gamut mapping processing (color compression). Further, the image processing apparatus (control unit 20) sets the first brightness difference between the first and second out-of-range pixels to a third brightness difference larger than the second brightness difference based on the second image correction parameter. After that, the input image corrected by the image correction parameter is subjected to gamut mapping processing (color compression).

  That is, when the gamut difference is relatively small (for example, when the adverse effect on the image quality is small even if the gradation difference of each out-of-range pixel is small), the image processing apparatus (control unit 20) One image correction parameter is set, and the brightness difference of each out-of-range pixel is slightly enlarged based on the first image correction parameter. Thereafter, the image processing apparatus (control unit 20) performs gamut mapping processing (color compression) on the input image corrected by the first image correction parameter (the brightness difference of each out-of-range pixel is slightly enlarged). As a result, the first and second out-of-range pixels (out-of-range pixels) fall within the output gamut (output color reproduction range).

  On the other hand, when the gamut difference is relatively large (for example, when the gradation difference between the pixels outside each range is small, the image quality is adversely affected), the image processing apparatus (control unit 20) Image correction parameters are set, and the brightness difference of each out-of-range pixel is enlarged relatively large based on the second image correction parameters. Thereafter, the image processing apparatus (control unit 20) performs gamut mapping processing (color compression) on the input image corrected by the second image correction parameter (the brightness difference between pixels outside each range is relatively large). As a result, the first and second out-of-range pixels (out-of-range pixels) fall within the output gamut (output color reproduction range). In this case, after the gamut mapping process (after color compression), the first and second out-of-range pixels (out-of-range pixels) are output gamut (output) while maintaining the brightness difference of the pixels before the gamut mapping process to some extent. Color reproduction range).

  Similarly, the image processing apparatus (control unit 20) variably controls the image correction parameter based on the number of out-of-range pixels that are out of the output color reproduction range. As a specific example, the image processing apparatus (control unit 20) sets the first image correction parameter based on the first out-of-range pixel number (relatively small value) and is larger than the first out-of-range pixel number. The second image correction parameter is set based on the second out-of-range pixel number (relatively large value). Further, the image processing apparatus (control unit 20) converts the first brightness difference between the first and second out-of-range pixels to a second brightness difference wider than the first brightness difference based on the first image correction parameter. After that, the input image corrected by the first image correction parameter is subjected to gamut mapping processing (color compression). Further, the image processing apparatus (control unit 20) sets the first brightness difference between the first and second out-of-range pixels to a third brightness difference larger than the second brightness difference based on the second image correction parameter. After that, the input image corrected by the image correction parameter is subjected to gamut mapping processing (color compression).

  That is, when the gamut difference is relatively small (for example, when the adverse effect on the image quality is small even if the gradation difference of each out-of-range pixel is small), the image processing apparatus (control unit 20) One image correction parameter is set, and the brightness difference of each out-of-range pixel is slightly enlarged based on the first image correction parameter. Thereafter, the image processing apparatus (control unit 20) performs gamut mapping processing (color compression) on the input image corrected by the first image correction parameter (the brightness difference of each out-of-range pixel is slightly enlarged). As a result, the first and second out-of-range pixels (out-of-range pixels) fall within the output gamut (output color reproduction range).

  On the other hand, when the gamut difference is relatively large (for example, when the gradation difference between the pixels outside each range is small, the image quality is adversely affected), the image processing apparatus (control unit 20) Image correction parameters are set, and the brightness difference of each out-of-range pixel is enlarged relatively large based on the second image correction parameters. Thereafter, the image processing apparatus (control unit 20) performs gamut mapping processing (color compression) on the input image corrected by the second image correction parameter (the brightness difference between pixels outside each range is relatively large). As a result, the first and second out-of-range pixels (out-of-range pixels) fall within the output gamut (output color reproduction range). In this case, after the gamut mapping process (after color compression), the first and second out-of-range pixels (out-of-range pixels) are output gamut (output) while maintaining the brightness difference of the pixels before the gamut mapping process to some extent. Color reproduction range).

  The image processing apparatus of the present embodiment is configured as follows, for example.

  An image processing apparatus corrects an image of bitmap data, and calculates an input unit for inputting bitmap data and a feature amount used for image correction from the bitmap data, and uses the feature amount The image correction parameters for the corrected pixel values are adjusted according to the characteristics of the image output device and output.

  Further, the image processing apparatus uses gamut information as a characteristic of the output device. Further, the image processing apparatus has a characteristic of the output device in accordance with the printing conditions of the output device (double-sided printing / single-sided printing, Nin1 printing for reducing N images for printing on the N side, and paper type). Use gamut information determined from defined color material limit values.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 11 ... External information input part, 12 ... Paper storage part, 13 ... Printing part, 20 ... Control part, 21 ... CPU, 22 ... Memory | storage device, 23 ... Calculation I / O part

Claims (13)

Based on the output color reproduction range of the image output apparatus that outputs an image based on the input image data and the color reproduction distribution of each pixel of the input image data, the output color reproduction range out of the pixels of the input image data is deviated. Control means for controlling an image correction parameter for correcting each out-of-range pixel;
Correction means for correcting the input image data based on the image correction parameters controlled by the control means;
An image processing apparatus.   The image processing apparatus according to claim 1, wherein the control unit controls the image correction parameter based on a color reproduction distribution of each out-of-range pixel.   The control means controls the image correction parameter based on a distance between a boundary of the output color reproduction range and a pixel outside the range out of the output color reproduction range among the pixels of the input image data. 2. The image processing apparatus according to 2.   The image processing apparatus according to claim 3, wherein the control unit controls the image correction parameter based on a sum of distances between a boundary of the output color reproduction range and pixels outside the range. The control means sets a first image correction parameter based on a first total value, sets a second image correction parameter based on a second total value larger than the first total value,
The correction means expands a first brightness difference between the first and second out-of-range pixels to a second brightness difference larger than the first brightness difference based on the first image correction parameter, and 5. The image processing according to claim 4, wherein the first brightness difference of the first and second out-of-range pixels is expanded to a third brightness difference larger than the second brightness difference based on the second image correction parameter. apparatus.   The image processing apparatus according to claim 1, wherein the control unit controls the image correction parameter based on the number of out-of-range pixels. The control means sets a first image correction parameter based on a first out-of-range pixel number, and sets a second image correction parameter based on a second out-of-range pixel number larger than the first out-of-range pixel number. Set,
The correction means expands a first brightness difference between the first and second out-of-range pixels to a second brightness difference larger than the first brightness difference based on the first image correction parameter, and 7. The image processing according to claim 6, wherein the first brightness difference of the first and second out-of-range pixels is expanded to a third brightness difference that is larger than the second brightness difference based on the second image correction parameter. apparatus.   The control means detects each out-of-range pixel outside the output color reproduction range based on output gamut information corresponding to the output color reproduction range and input gamut information corresponding to the input color reproduction range. 8. The image processing apparatus according to any one of items 7.   The image processing apparatus according to claim 8, wherein the control unit detects each out-of-range pixel that is out of the output color reproduction range based on the output gamut information corresponding to an output condition of the image output apparatus.   The control means outputs the output based on the output gamut information corresponding to at least one print setting of single-sided printing, double-sided printing, and Nin1 printing for reducing N images for printing on N-side to one side. The image processing apparatus according to claim 8, wherein each out-of-range pixel out of the color reproduction range is detected.   The image processing apparatus according to claim 1, further comprising color compression means for color-compressing the input image data corrected by the correction means.   The image processing apparatus according to claim 11, wherein the color compression unit fits each out-of-range pixel into the output color reproduction range by the color compression. Based on the output color reproduction range of the image output apparatus that outputs an image based on the input image data and the color reproduction distribution of each pixel of the input image data, the output color reproduction range out of the pixels of the input image data is deviated. Control image correction parameters to correct each out-of-range pixel,
An image processing method for correcting the input image data based on the image correction parameter controlled by the control means.

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