JP2013250314A - Image processor, display device, information processor and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processor able to improve image quality even in the case where neither a pixel with a low luminance value nor a pixel with a high luminance value is present.SOLUTION: A correction determining unit 21 determines whether all the respective luminance values of input image data are present within a specific luminance range smaller than the entire luminance range or not. If any of the luminance values is outside the specific luminance range, a correcting unit 22 converts the luminance values according to a predetermined tone curve. Conversely, if all the luminance values are within the specific luminance range, the correcting unit 22 corrects the tone curve on the basis of the input luminance range in which the luminance values are present, and converts the luminance values according to the corrected tone curve.

Description

  The present invention relates to an image processing apparatus that converts each luminance value of image data according to a tone curve.

  In a display device that displays an image such as an LCD (Liquid Crystal Display), the image quality may be lowered depending on a luminance histogram that is a distribution of luminance values of the display image.

  For example, as in the luminance histogram shown in FIG. 7A, when there are many pixels (pixels) with low luminance values and the display image is entirely dark, black pixels are generated in which pixels with low luminance values in the display image are painted black. As a result, the image quality may be lowered.

  Also, as in the luminance histogram shown in FIG. 7B, when there are many pixels with high luminance values and the display image is bright overall, whiteout occurs in which pixels with high luminance values in the display image are painted white, resulting in image quality. May become low.

  Furthermore, as in the luminance histogram shown in FIG. 7C, when the luminance values of the pixels are gathered in the intermediate gradation and the contrast of the display image is low, the brightness of the display image is not clearly recognized, and the display image is thin overall. It may be visible.

  On the other hand, Patent Document 1 describes an image processing device that converts each luminance value of image data according to a tone curve corresponding to a luminance histogram of the image data. The tone curve is a conversion curve indicating the correspondence between the luminance value before conversion and the luminance value after conversion.

  For example, when there are many pixels with low luminance values, the image processing apparatus described in Patent Document 1 converts each luminance value according to a tone curve in which a region with a low luminance value is a convex curve, and has a high luminance value. When there are many pixels, each luminance value of the image data is converted according to a tone curve in which a region having a high luminance value becomes a downwardly convex curve.

  This makes it possible to reduce pixels with low luminance values when the display image is totally dark, and reduce pixels with high luminance when the display image is overall bright, so It becomes possible to suppress.

  In addition, when the contrast of the display image is low, the image processing apparatus described in Patent Document 1 is a tone curve in which a region having a low luminance value has a downward convex curve and a region having a high luminance value has a convex curve upward. According to the above, each luminance value of the image data is converted. This makes it possible to make pixels with low luminance values darker and pixels with high luminance values brighter, so that the brightness of the display image can be clearly recognized.

JP 2007-0697907

  However, in the image processing apparatus described in Patent Document 1, the luminance values of the image data are gathered in the intermediate gradation, and the luminance value is low even when there are no pixels with low luminance values or pixels with high luminance values. Each luminance value of the image data is converted according to a tone curve in which the region has a downwardly convex curve and the region having a high luminance value becomes an upwardly convex curve.

  For this reason, low brightness areas and high brightness areas in the tone curve are not used, and pixels with low brightness values or pixels with high brightness values do not exist in the converted image data. There is. In this case, the contrast of the display image does not increase, and there is a possibility that the image quality cannot be increased.

  An object of the present invention is to provide an image processing device, a display device, and an image processing method capable of improving image quality even when there is no pixel having a low luminance value or a pixel having a high luminance value.

  An image processing apparatus according to the present invention includes a correction determination unit that determines whether all the luminance values of each pixel of input image data are in a specific luminance range smaller than the entire luminance range, and any of the luminance values. If the luminance value is outside the specific luminance range, each luminance value is converted according to a predetermined tone curve, and if all the luminance values are within the specific luminance range, the luminance value is present in the tone curve. A correction unit that performs correction based on the input luminance range and converts each luminance value according to the corrected tone curve.

  The display device according to the present invention includes the image processing device and a display unit that displays an output image indicated by output image data that is input image data in which each luminance value is converted by the image processing device.

  An information processing apparatus according to the present invention includes the display device.

  According to the image processing method of the present invention, it is determined whether all the luminance values of each pixel of the input image data are present in a specific luminance range smaller than the total luminance range, and any one of the luminance values is specified. When the luminance value is outside the luminance range, each luminance value is converted according to a predetermined tone curve, and when all the luminance values are within the specific luminance range, the tone curve is converted into the input luminance range where each luminance value exists. And each luminance value is converted in accordance with the corrected tone curve.

  According to the present invention, it is possible to improve the image quality even when there is no pixel having a low luminance value or a pixel having a high luminance value.

It is a block diagram which shows the structure of the display apparatus of the 1st Embodiment of this invention. It is a figure for demonstrating an example of level correction. It is a figure which shows an example of a base tone curve. It is a figure which shows the other example of a base tone curve. It is a figure which shows the other example of a base tone curve. It is a figure which shows the other example of a base tone curve. It is a figure which shows an example of a correction | amendment tone curve. It is a figure which shows the other example of a correction | amendment tone curve. It is a figure which shows the other example of a correction | amendment tone curve. It is a figure which shows the other example of a correction | amendment tone curve. It is a flowchart for demonstrating operation | movement of the display apparatus of the 1st Embodiment of this invention. It is a figure which shows the structure of the display apparatus of the 2nd Embodiment of this invention. It is a figure which shows an example of a brightness | luminance histogram. It is a figure which shows the other example of a brightness | luminance histogram. It is a figure which shows the other example of a brightness | luminance histogram.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, components having the same function may be denoted by the same reference numerals and description thereof may be omitted.

  FIG. 1 is a block diagram showing the configuration of the display device according to the first embodiment of the present invention. In FIG. 1, the display device includes an image processing unit 1 and a display unit 2. Note that the display device may be incorporated in the information processing apparatus. Examples of the information processing apparatus include a mobile phone, a smartphone, a game machine, a tablet PC (Personal Computer), a notebook PC, and a PDA (Personal Digital Assistant: portable information terminal).

  The image processing unit 1 converts the luminance value of each pixel of the input image data, which is input image data, into an output luminance value according to a tone curve, and converts the input luminance data into an output luminance value as output image data. An image processing apparatus that generates data. The display unit 2 displays an output image indicated by the output image data generated by the image processing unit 1.

  Note that the image data may indicate a still image or a moving image. The luminance value is, for example, a Y value (0 to 255) in the image data in the YCbCr format. Hereinafter, the luminance value is assumed to be a Y value, and the luminance value of each pixel of the input image data may be referred to as an input luminance value. The tone curve is a conversion curve for converting the input luminance value, and more specifically, a curve indicating the correspondence between the input luminance value and the output luminance value.

  Specifically, the image processing unit 1 includes a luminance histogram collection unit 11, a level correction determination unit 12, an image processing determination unit 13, and a luminance tone curve setting unit 14.

  The luminance histogram collection unit 11 is a creation unit that creates a luminance histogram of input image data based on the input image data. The luminance histogram is data indicating the distribution of each input luminance value of the input image data. More specifically, the luminance histogram is data indicating the number of pixels of the luminance value for each luminance value.

  The level correction determination unit 12 is a correction determination unit that determines whether level correction is performed on input image data based on the luminance histogram created by the luminance histogram collection unit 11.

  More specifically, the level correction determination unit 12 determines whether or not to perform level correction by determining whether or not all of the input luminance values are present in the specific luminance range based on the luminance histogram. . At this time, the level correction determination unit 12 determines that the level correction is performed when all of the input luminance values are within the specific luminance range, and the level correction is performed when any of the input luminance values is outside the specific luminance range. Is determined not to be performed.

  The specific luminance range is a range smaller than the total luminance range (0 ≦ Y ≦ 255) that the input luminance value can take. For example, the minimum luminance value of the specific luminance range is larger than the minimum luminance value (Y = 0) of the entire luminance range, and the maximum luminance value of the specific luminance range is the maximum luminance value (Y = 255) of the entire luminance range. ) Is smaller. The specific luminance range may be set in advance or may be set by a user who uses the display device.

  The level correction is to correct the brightness and contrast of the image indicated by the input image data, and is performed by the luminance tone curve setting unit 14 as will be described later.

  FIG. 2 is a diagram for explaining an example of level correction.

  As shown in FIG. 2A, all input luminance values of the input image data are assumed to be in the input luminance range from 50 to 200. In this case, if the tone curve is defined by a straight line passing through (input luminance value, output luminance value) = (0, 0) and (255, 255), for example, the output luminance value is 0 to 49. , 201 to 255 no longer exist, so the output image may be an image with no clear contrast.

  The level correction is to correct the tone curve so that the output luminance range in which the output luminance value exists is widened, thereby making it possible to make the output image clear and bright.

  For example, the level correction is performed by compressing a tone curve defined by a straight line passing through (input luminance value, output luminance value) = (0, 0) and (255, 255) in the axial direction of the input luminance value, This is realized by correcting the tone curve so that it falls within the input luminance range (50 ≦ Y ≦ 200). In this case, the corrected tone curve is a straight line passing through (input luminance value, output luminance value) = (50, 0) and (200, 255), and the luminance histogram after level correction is shown in FIG. It will be shown in Therefore, the contrast of the output image is increased, and the output image can be made a clear and bright image.

  Returning to the description of FIG. When it is determined that level correction is to be performed, the level correction determination unit 12 corrects the luminance histogram based on the input luminance range. Specifically, the level correction determination unit 12 outputs an output luminance value obtained by converting each input luminance value according to the corrected tone curve in the input luminance range (50 to 200 in the case of FIG. 2) in the luminance histogram. The luminance histogram is expanded in the axial direction of the input luminance value so as to coincide with the luminance range (0 to 255 in the case of FIG. 2).

  Then, the level correction determination unit 12 outputs the corrected luminance histogram to the image processing determination unit 13. Further, the level correction determination unit 12 outputs level correction information indicating the input luminance range to the luminance tone curve setting unit 14. In the present embodiment, the input luminance range includes the lowest minimum luminance value Ymin (50 in the case of FIG. 2) among the input luminance values of the input image and the highest maximum luminance among the input luminance values of the input image. It is assumed that it is represented by a value Ymax (200 in the case of FIG. 2).

  On the other hand, when it is determined that level correction is not performed, the level correction determination unit 12 outputs the luminance histogram calculated by the luminance histogram collection unit 11 to the image processing determination unit 13 as it is.

  The image processing determination unit 13 is an analysis unit that analyzes the luminance histogram output from the level correction determination unit 12 and outputs the analysis result to the luminance tone curve setting unit 14.

  More specifically, the image processing determination unit 13 classifies the luminance histogram into any of a plurality of predetermined patterns, and outputs an analysis result indicating the classified pattern to the luminance tone curve setting unit 14.

In the present embodiment, the image processing determination unit 13 classifies the luminance histogram into any of the following patterns A to D.
Pattern A: Crushed black image (image in which the luminance histogram is biased toward the low luminance value side)
Pattern B: Whiteout image (image with luminance histogram biased toward high luminance value)
Pattern C: Black-out and white-out image (image in which the luminance histogram is biased toward the low luminance value side and the high luminance value side)
Pattern D: Not applicable image (image not corresponding to patterns A to C)
For example, the image processing determination unit 13 holds representative luminance histograms A ′ to C ′ corresponding to the patterns A to C in advance. Then, the image processing determination unit 13 performs pattern matching between the actual histogram that is the luminance histogram from the level correction determination unit 12 and each of the representative luminance histograms A ′ to C ′, and the actual histogram and the representative luminance The similarity with each of the histograms A ′ to C ′ is obtained. The level correction determination unit 12 classifies the luminance histograms into patterns A to C corresponding to the representative luminance histograms A ′ to C ′ having the highest similarity when at least one of the similarities is equal to or greater than a threshold value. When all the degrees are less than the threshold, the luminance histogram is classified into the pattern D.

  The luminance tone curve setting unit 14 is a tone curve used for conversion of each input luminance value of the input image data based on the analysis result from the image processing determination unit 13 and the level correction information from the level correction determination unit 12. Determine the tone curve used.

  Specifically, first, the luminance tone curve setting unit 14 holds in advance four base tone curves that are tone curves corresponding to the patterns A to D, and from these patterns, the pattern indicated by the analysis result A base tone curve corresponding to is selected as a predetermined tone curve.

  3A to 3D are diagrams showing examples of the base tone curve.

  The base tone curve shown in FIG. 3A is a tone curve corresponding to the pattern A (black crushing image), and a region with a low luminance value is a convex curve so that pixels with a low luminance value in the output image become brighter. It has become.

  The base tone curve shown in FIG. 3B is a tone curve corresponding to the pattern B (out-of-white image), and a region having a high luminance value becomes a downward convex curve so that pixels having a high luminance value in the output image are darkened. It has become.

  The base tone curve shown in FIG. 3C is a tone curve corresponding to the pattern C (blackout & whiteout image). Pixels with low brightness values in the output image become bright and pixels with high brightness values in the output image appear. A region with a low luminance value has an upwardly convex curve, and a region with a high luminance value has a downwardly convex curve so as to be dark.

  The base tone curve shown in FIG. 3D is a tone curve corresponding to the pattern D (non-applicable image), and a region having a low luminance value becomes a downward convex curve so that the contrast of the output image is high. The high region is a convex curve. The base tone curve corresponding to the pattern D (non-applicable image) may be a straight line (input luminance value Y = output luminance value Y).

  Returning to the description of FIG. When a predetermined tone curve is selected, the luminance tone curve setting unit 14 confirms whether or not the level correction determination unit 12 determines to perform level correction.

  When level correction is not performed, the luminance tone curve setting unit 14 determines a predetermined tone curve as a use tone curve.

  On the other hand, when performing level correction, the luminance tone curve setting unit 14 corrects a predetermined tone curve based on the level correction information in order to perform input image data level correction, and uses the corrected tone curve as a tone curve to be used. To decide.

  In the tone curve correction, as described above, the luminance tone curve setting unit 14 compresses the predetermined tone curve in the axial direction of the input luminance value so that the predetermined tone curve falls within the input luminance range.

  4A to 4D are diagrams illustrating an example of a corrected tone curve that is a corrected tone curve. Each of the correction tone curves shown in FIGS. 4A to 4D is obtained by compressing the base tone curve shown in each of FIGS. 3A to 3D in the axial direction of the input luminance value so as to be within the input luminance range.

  Returning to the description of FIG. When the use tone curve is determined, the brightness tone curve setting unit 14 converts each input brightness value of the input image data into an output brightness value according to the use tone curve, and generates output image data.

  Next, the operation of the display device will be described.

  FIG. 5 is a flowchart for explaining an example of the operation of the display device.

  First, image data is input to the luminance histogram collection unit 11. The luminance histogram collection unit 11 analyzes each input luminance value of the input image data that has been input, and creates a luminance histogram of the input image data. Then, the luminance histogram collection unit 11 outputs the input image data and the luminance histogram to the level correction determination unit 12 (step S101).

  When the level correction determination unit 12 receives the input image data and the luminance histogram, the level correction determination unit 12 determines whether or not all the input luminance values are included in the specific luminance range based on the luminance histogram. It is then determined whether or not level correction is performed (step S102).

  When any one of the input luminance values is not included in the specific luminance range, the level correction determination unit 12 determines that level correction is not performed, and outputs the input image data and the luminance histogram as they are to the image processing determination unit 13 ( Step S103).

  On the other hand, when all of the input luminance values are included in the specific luminance range, the level correction determination unit 12 determines to perform level correction, and from the luminance histogram, the minimum luminance value Ymin that is the minimum value of the input luminance values, The maximum luminance value Ymax, which is the maximum value of the input luminance value, is acquired, and the luminance histogram is corrected based on the input luminance range from the minimum luminance value Ymin to the maximum luminance value Ymax. Then, the level correction determination unit 12 outputs the corrected luminance histogram and the input image data to the image processing determination unit 13, and sets level correction information indicating the minimum luminance value Ymin and the maximum luminance value Ymax as a luminance tone curve setting. It outputs to the part 14 (step S104).

  When receiving the luminance histogram and the input image data, the image processing determination unit 13 classifies the received luminance histogram into any one of the patterns A to D, and generates the classified pattern as an analysis result. Then, the image processing determination unit 13 outputs the analysis result and the input image data to the luminance tone curve setting unit 14 (step S105).

  The luminance tone curve setting unit 14 receives an analysis result and input image data from the luminance tone curve setting unit 14. When the level correction determination unit 12 outputs level correction information in step S104, the luminance tone curve setting unit 14 receives the level correction information.

  Then, the brightness tone curve setting unit 14 selects a base tone curve corresponding to the pattern indicated by the analysis result as a predetermined tone curve from the four base tone curves held in advance (step S106).

  When a predetermined tone curve is selected, the luminance tone curve setting unit 14 confirms whether or not level correction is performed (step S107). For example, the luminance tone curve setting unit 14 confirms whether or not level correction information has been received. When the level correction information is received, the luminance tone curve setting unit 14 determines that level correction is to be performed and does not receive level correction information. It is determined that level correction is not performed.

  When level correction is not performed, the luminance tone curve setting unit 14 converts each input luminance value of the input image data into an output luminance value according to a predetermined tone curve, and generates output image data (step S108).

  On the other hand, when performing level correction, the luminance tone curve setting unit 14 corrects a predetermined tone curve so that it falls within the input luminance range from the minimum luminance value Ymin to the maximum luminance value Ymax indicated by the level correction information. Then, the luminance tone curve setting unit 14 converts each input luminance value of the input image data into an output luminance value according to the corrected tone curve, and generates output image data (step S109).

  When the output image data is generated, the luminance tone curve setting unit 14 outputs the output image data to the display unit 2. When receiving the output image data, the display unit 2 displays the output image indicated by the output image data (step S110).

  With the above operation, when the luminance histogram is classified into any of patterns A to C in step S105 and it is determined in step S102 that level correction is to be performed, at least one of blackening and overexposure and the level is determined. It will be corrected.

  If the luminance histogram is classified into any of patterns A to C in step S105 and it is determined in step S102 that level correction is not performed, level correction is not performed, and at least one of blackening and whiteout is performed. Will be corrected.

  If the luminance histogram is classified into the pattern D in step S105 and it is determined in step S102 that level correction is performed, only level correction is performed.

  If it is determined in step S105 that the luminance histogram is classified as pattern D and it is determined in step S102 that level correction is not performed, neither level correction nor blackout and whiteout correction is performed.

  As described above, according to the present embodiment, when all input luminance values of the input image data exist in the specific luminance range, the tone curve is corrected based on the input luminance range. Even when there is no pixel having a high luminance value, it is possible to increase the image contrast by increasing the contrast of the image.

  In the present embodiment, since the tone curve is compressed in the axial direction of the luminance value, the shape of the tone curve can be maintained, and the image quality can be further improved.

  In this embodiment, the tone curve is corrected so as to be within the input luminance range, so that the contrast of the image can be maximized.

  In the present embodiment, since each input luminance value is obtained with a tone curve corresponding to the luminance histogram, it is possible to correct not only image contrast but also black crushing and whiteout. Therefore, it is possible to improve the image quality.

  Further, in the present embodiment, when level correction is performed, the luminance histogram is also corrected, and each input luminance value is converted with a tone curve corresponding to the corrected luminance histogram. Therefore, when the contrast of the image is increased. It is possible to suppress occurrence of black crushing or whiteout. Therefore, it is possible to improve the image quality.

  Next, a second embodiment will be described.

  FIG. 6 is a diagram illustrating a configuration of the image processing apparatus according to the present embodiment. In FIG. 6, the image processing apparatus includes a correction determination unit 21 and a correction unit 22.

The correction determination unit 21 determines whether or not all the luminance values of each pixel of the input image data are present in a specific luminance range smaller than the entire luminance range. The correction determination unit 21 may perform this determination based on the luminance histogram, but may perform this determination by analyzing image data.
The correction unit 22 converts each luminance value according to a predetermined tone curve when any one of the luminance values is outside the specific luminance range. Further, the correction unit 22 corrects the tone curve based on the input luminance range in which each luminance value exists when all the luminance values are present in the specific luminance range, and according to the corrected tone curve, Convert luminance values,
Also in the present embodiment, as in the first embodiment, it is possible to increase the image contrast and improve the image quality.

  In each embodiment described above, the illustrated configuration is merely an example, and the present invention is not limited to the configuration.

DESCRIPTION OF SYMBOLS 1 Image processing part 2 Display part 11 Luminance histogram collection part 12 Level correction determination part 13 Image processing determination part 14 Luminance tone curve setting part 21 Correction determination part 22 Correction part

Claims (8)

A correction determination unit that determines whether all of the luminance values of each pixel of the input image data are present in a specific luminance range smaller than the entire luminance range;
When any one of the luminance values is outside the specific luminance range, each luminance value is converted according to a predetermined tone curve, and when all the luminance values are within the specific luminance range, the tone curve is An image processing apparatus comprising: a correction unit that performs correction based on an input luminance range in which each luminance value exists and converts each luminance value according to the corrected tone curve.   The image processing according to claim 1, wherein the correction unit compresses the tone curve in the axial direction of the luminance value based on the input luminance range when all the luminance values are present in the specific luminance range. apparatus.   The image processing according to claim 1, wherein the correction unit corrects the tone curve so that the tone curve falls within the input luminance range when all the luminance values are present in the specific luminance range. apparatus. A creation unit for creating a luminance histogram of the image data;
An analysis unit that classifies the luminance histogram into any of a plurality of predetermined patterns;
The correction unit holds a plurality of base tone curves corresponding to the plurality of patterns, and selects a base tone curve corresponding to the pattern classified by the analysis unit as the predetermined tone curve. 4. The image processing apparatus according to any one of items 3. The correction determination unit corrects the luminance histogram based on the input luminance range when all the luminance values are included in the specific luminance range,
The image processing apparatus according to claim 4, wherein the analysis unit classifies the corrected luminance histogram when all the luminance values are included in the specific luminance range. An image processing apparatus according to any one of claims 1 to 5,
A display unit that displays an output image indicated by output image data that is input image data in which each luminance value is converted by the image processing device.   An information processing apparatus comprising the display device according to claim 6. It is determined whether all the luminance values of each pixel of the input image data are present in a specific luminance range smaller than the entire luminance range,
When any one of the luminance values is outside the specific luminance range, each luminance value is converted according to a predetermined tone curve,
When all the luminance values are present in the specific luminance range, the tone curve is corrected based on the input luminance range in which each luminance value exists, and each luminance value is converted according to the corrected tone curve. Processing method.

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