JP5111310B2 - Image processing method and image processing apparatus - Google Patents

Description

  The present invention relates to an image processing method and an image processing apparatus that execute dynamic γ processing.

  There is an image processing method that adaptively executes γ conversion processing according to the characteristics of an input video signal. In this specification, this processing is referred to as dynamic γ processing. The flow of dynamic γ processing will be described by taking the case where the image data is 8 bits as an example. First, as shown in FIG. 8, for a pixel in one frame, a histogram is detected with the horizontal axis representing luminance gradation and the vertical axis representing the number of pixels. Next, as indicated by arrows in FIG. 8, the minimum luminance value and the maximum luminance value in one frame are detected from the histogram. Subsequently, as shown in FIG. 9, a gradation conversion curve is generated so that the minimum luminance value is output to 0 gradation and the maximum luminance value is output to 255 gradation, and γ conversion is performed.

  However, if γ conversion is performed at the same time as the histogram detection for one frame is completed, the tone conversion curve cannot be rewritten in time, and there is a problem that the tone conversion curve cannot be applied to the frame in which the histogram is detected.

  As a countermeasure to this problem, there is a method described in Japanese Patent Application Laid-Open No. 2006-295686 (Patent Document 1). This performs image processing in the order of histogram detection, IP conversion (interlace-progressive conversion), and dynamic γ processing using histogram information. An image processing apparatus described in Patent Literature 1 is shown in FIG.

Patent Document 1 describes that a frame memory is required for IP conversion, and an image is delayed by one frame. Therefore, in the processing order shown in FIG. 10, frame delay occurs in IP conversion, so that it is possible to perform dynamic γ processing without delay for the input video signal from which the histogram is detected.
JP 2006-295686 A

  In general, an image displayed on a television is subjected not only to IP conversion and dynamic γ processing but also to various image processing. One of the processes is an enhancer process (outline enhancement process). The enhancer process extracts the high-frequency component of the input video signal to enhance the contour of the image, and adds it to the original input video signal to add undershoot and overshoot to the contour portion of the image to enhance the contour. This is a process for performing an outline-enhanced signal. In the enhancer process, when a waveform as shown in FIG. 11A is input, a signal with an undershoot and overshoot component as shown in FIG. 11B is output. For this reason, when an undershoot is applied, a pixel having a darker luminance value than the input video signal is generated, and when an overshoot is applied, a pixel having a brighter luminance value than the input video signal is generated.

  In the enhancer process, it is considered preferable to perform the enhancer process after the IP conversion because the process for the progressive signal has a higher degree of freedom of selection of the emphasized frequency than the process for the interlaced signal.

However, for example, when image processing is executed in the processing order of histogram detection, IP conversion, enhancer processing, and dynamic γ processing, there are the following problems. In the gradation conversion curve creation, a gradation conversion curve as shown in FIG. 9 is created from a histogram that does not reflect undershoot and overshoot given by the enhancer process.
Due to the undershoot that occurs in the enhancer process, the minimum brightness value of the image is smaller than before the enhancer process, and due to the overshoot, the maximum brightness value of the image is greater than that before the enhancer process. However, in the gradation conversion curve of FIG. 9, the undershoot generated after the enhancer process is output at 0 gradation, and the overshoot is output at 255 gradation. For this reason, there is a problem that the effects of undershoot and overshoot are canceled and the sharpness of the image improved by the enhancer processing is reduced.

  The present invention has been made in view of the above circumstances, and the objects thereof are as follows. That is, it is an object to provide an image processing method and an image processing apparatus that perform dynamic γ processing so as not to suppress the effects of undershoot and overshoot imparted by enhancer processing in order to improve sharpness.

In order to achieve the above object, the first aspect of the present invention employs the following configuration. That is, detection means for detecting the minimum and maximum luminance values of pixels in an image included in the video signal, and input in gradation conversion based on the minimum and maximum luminance values detected by the detection means A creation unit that creates a gradation conversion curve that indicates the relationship between the luminance value and the output luminance value, and a process that performs the enhancer process on the image according to an enhancer intensity that indicates the intensity of the enhancer process that enhances the contour of the image And gradation conversion means for performing gradation conversion on the image subjected to the enhancer processing by the processing means using the gradation conversion curve created by the creation means, and the detection The minimum value and the maximum value of the luminance value detected by the means are changed according to the enhancer intensity, and the creating means uses the changed minimum value and the changed maximum value after the change to change the gradation conversion card. An image processing apparatus characterized by creating a.

In the second invention of the present invention, the following configuration is adopted. That is, first detection means for detecting a histogram from luminance values of pixels in an image included in a video signal, correction means for correcting the histogram detected by the first detection means with a low-pass filter, and low-pass filter by the correction means Second detection means for detecting a minimum value and a maximum value of the luminance value in the histogram corrected in step (b), and an input luminance value in gradation conversion based on the minimum value and the maximum value detected by the second detection means; Creating means for creating a gradation conversion curve indicating a relationship between output luminance values; processing means for performing enhancer processing on the image according to enhancer strength indicating the strength of enhancer processing for enhancing the contour of the image; Using the gradation conversion curve created by the creating means, a scale is applied to an image that has undergone the enhancer processing by the processing means. A gradation conversion unit for converting an image processing apparatus characterized by having a.

In the third invention of the present invention, the following configuration is adopted. That is, the detecting means detects the minimum and maximum luminance values of the pixels in the image included in the video signal, and the creating means sets the minimum and maximum luminance values detected in the detecting step. A creation step for creating a gradation conversion curve indicating a relationship between an input luminance value and an output luminance value in gradation conversion,
A processing step in which processing means performs enhancer processing on the image according to an enhancer strength indicating the strength of enhancer processing that emphasizes the contour of the image, and a gradation conversion means is created in the creation step. A gradation conversion step for performing gradation conversion on an image that has been subjected to the enhancer process in the processing step using a gradation conversion curve, and a minimum luminance value detected in the detection step; In the image processing method, the maximum value is changed according to the enhancer intensity, and in the creation step, the gradation conversion curve is created using the changed minimum value and the changed maximum value after the change. is there.

In the fourth aspect of the present invention, the following configuration is adopted. That is, the first detection unit detects a histogram from the luminance value of the pixel in the image included in the video signal, and the correction unit corrects the histogram detected in the first detection step with a low-pass filter. A correction step; a second detection step in which the second detection means detects a minimum value and a maximum value of luminance values in the histogram corrected by the low-pass filter in the correction step; and a creation means in the second detection step. A creation step for creating a gradation conversion curve indicating a relationship between an input luminance value and an output luminance value in gradation conversion based on the detected minimum value and maximum value, and processing means enhances the contour of the image A processing step for performing enhancer processing on the image in accordance with enhancer strength indicating the strength of enhancer processing, and a gradation converting means, A gradation conversion step of performing gradation conversion on the image subjected to the enhancer processing in the processing step using the gradation conversion curve created in the creation step. Is the method.

  According to the present invention, it is possible to perform dynamic γ processing that does not suppress the effects of undershoot and overshoot imparted by the enhancer processing in order to improve sharpness.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings.

<Example 1>
FIG. 1 shows a block diagram of an image processing apparatus in this embodiment. This image processing apparatus includes a histogram detection unit 101, an enhancer strength setting unit 102, a Min / Max detection unit 103, a Min / Max change unit 104, a gradation conversion curve creation unit 105, an IP conversion unit 106, an enhancer unit 107, and a γ conversion. Part 108. The operation of this embodiment configured as described above will be described below.

  The histogram detection unit 101 detects a histogram of 256 luminance signals having a gradation of 0 to 255 from a luminance signal in one frame from an input video signal.

  The enhancer strength setting unit 102 sets the enhancer strength G. Then, values are output to the Min / Max changing unit 104 and the enhancer unit 107 according to the set strength. This output value is a value specified by the user, for example. In this embodiment, the output value is 0, 1 or 2, and “2” is set when the enhancer strength is increased, “1” is set when the strength is intermediate, and “0” is set when the strength is decreased. Output as. In this embodiment, the enhancer strength G output from the enhancer strength setting unit 102 is “2”.

  The Min / Max detection unit 103 detects the minimum luminance value and the maximum luminance value in one frame from the histogram of the luminance signal detected by the histogram detection unit 101. In this embodiment, the minimum luminance value detected by the Min / Max detection unit 103 is Min, and the maximum luminance value is Max. The luminance value detection unit of the present invention corresponds to the Min / Max detection unit 103 in the present embodiment.

  The Min / Max changing unit 104 changes Min and Max in one frame detected by the Min / Max detecting unit 103, and the Min / Max changing unit 104 has tables as shown in FIGS. is there. In these tables, a minimum luminance value change amount and a maximum luminance value change amount corresponding to the enhancer strength G output from the enhancer strength setting unit 102 are stored. In this embodiment, the updated minimum luminance value and the updated maximum luminance value after being updated by the Min / Max changing unit 104 are set as Min_a and Max_a, respectively. In the present embodiment, the enhancer strength G output by the enhancer strength setting unit 102 is 2, so the values Min_a = Min−10 and Max_a = Max + 10 are obtained from the tables of FIGS. 2A and 2B. . The luminance value changing unit of the present invention corresponds to the Min / Max changing unit 104 in the present embodiment.

By such a method, it is possible to predict a change in the minimum luminance value and the maximum luminance value in one screen that changes due to occurrence of undershoot and overshoot in the enhancer unit 107. In addition, when calculating | requiring Min_a and Max_a, it is not restricted to the method by a table like a present Example, You may carry out with the calculation formula which is a function of G.

  The tone conversion curve creating unit 105 creates a tone conversion curve from Min_a and Max_a changed by the Min / Max changing unit 104. A gradation conversion curve created from Min and Max detected by the Min / Max detection unit 103 is indicated by a dotted line in FIG. Here, as described above, Min and Max are the minimum luminance value and the maximum luminance value detected from the histogram before the enhancer processing. FIG. 3 shows the relationship between the input luminance on the horizontal axis and the output luminance on the vertical axis corresponding thereto. However, undershoot and overshoot occur due to the enhancer process, so that a pixel having a pixel value smaller than Min or a pixel larger than Max is formed. In the gradation conversion curve indicated by the dotted line in FIG. 3, these gradations are compressed.

  On the other hand, in the present embodiment, the gradation conversion curve is created from the values Min_a = Min−10 and Max_a = Max + 10 obtained by the Min / Max changing unit 104, so the gradation conversion curve as shown by the solid line in FIG. become. This gradation conversion curve is created by predicting changes in the minimum luminance value and the maximum luminance value in one frame that change due to undershoot and overshoot that occur after enhancer processing. Therefore, it is possible to perform gradation conversion that does not compress the luminance value of the pixel generated by undershoot and overshoot and does not cancel the effect of the enhancer processing.

  The IP conversion unit 106 performs processing for converting the input interlace signal into a progressive signal. The IP conversion unit 106 includes a frame memory, and an image for one frame is delayed when performing IP conversion. Therefore, it is possible to create a gradation conversion curve for the frame in which the histogram is detected, and to secure time for performing dynamic γ processing.

  The enhancer unit 107 performs enhancer processing according to the output value from the enhancer strength setting unit 102. In the present embodiment, since the enhancer strength setting unit 102 sets “2” as the enhancer strength, the applied undershoot and overshoot increase.

  The γ conversion unit 108 performs gradation conversion according to the input luminance data using the gradation conversion curve created by the gradation conversion curve creation unit 105 from the input contour-enhanced signal, and the data after γ conversion is converted into data. Output. Note that the gradation conversion unit of the present invention corresponds to the γ conversion unit 108 in this embodiment.

  In the image processing apparatus having the above-described configuration, it is possible to create a gradation conversion curve after predicting the effects of undershoot and overshoot imparted by enhancer processing to improve sharpness. Thereby, the problem that the dynamic γ processing suppresses the effect of the enhancer processing can be reduced. In addition, dynamic γ processing can be performed on a frame in which a histogram is detected without delay.

<Example 2>
FIG. 4 shows a block diagram of the image processing apparatus in the present embodiment. This image processing apparatus includes an edge intensity detection unit 201 in addition to the image processing apparatus of FIG. 1 used in the first embodiment. The same blocks as those in FIG. 1 used in Example 1 are denoted by the same reference numerals. The operation of this embodiment configured as described above will be described below.

The edge strength detection unit 201 detects a forward difference absolute value S1 of luminance data in one frame. A larger advance difference absolute value S1 means that the image includes a larger edge. In this embodiment, the advance difference absolute value S1 is a horizontal advance difference absolute value as shown in (Equation 1) for calculating the absolute value of the luminance difference between adjacent pixels.
| Y (i, j) -Y (i + 1, j) | (Formula 1)

Here, Y (i, j) is the luminance data of the position (i, j) of the (x, y) coordinates in the screen. In addition to (Equation 1), the edge strength may be obtained by detecting the absolute value of the forward difference in the vertical direction as shown in (Equation 2).
| Y (i, j) −Y (i, j + 1) | (Formula 2)

  Next, the edge strength detection unit 201 outputs the edge strength S according to the maximum value in one frame of the detected forward difference absolute value S1. In this embodiment, the edge strength has three levels of 0, 1, and 2. Here, it is assumed that arbitrary integers A and B have a relationship of “0 <B <A”. When the maximum value in one frame of S1 detected by the edge strength detection unit 201 is A or more, “S = 2”, when it is B or less, “S = 0”, and when B <S1 <A, “S” = 1 "is output. In this embodiment, the edge strength S output from the edge strength detection unit 201 is “1”.

  The Min / Max changing unit 104 changes the minimum luminance value and the maximum luminance value in one frame detected by the Min / Max detecting unit 103. The Min / Max changing unit 104 has tables as shown in FIGS. These tables store values for changing the minimum luminance value and the maximum luminance value according to the enhancer strength G output from the enhancer strength setting unit 102 and the edge strength S output from the edge strength detection unit 201. Yes. In this embodiment, the updated minimum luminance value and the updated maximum luminance value after being updated by the Min / Max changing unit 104 are set as Min_b and Max_b, respectively. In this embodiment, the edge strength S output from the edge strength detection unit 201 is “1”, and the enhancer strength G output from the enhancer strength setting unit 102 is “2”.

  In the Min / Max changing unit 104, values of Min_b = Min-7 and Max_b = Max + 7 are obtained from the tables of FIGS. 5A and 5B. In the present embodiment, in this way, changes in the minimum luminance value and the maximum luminance value that change due to occurrence of undershoot and overshoot in the enhancer unit 107 are predicted from the edge strength S and the enhancer strength G. Therefore, the minimum luminance value and the maximum luminance value after the enhancer process can be predicted with higher accuracy.

  As in the first embodiment, the tone conversion curve creating unit 105 creates a tone conversion curve from the values Min_b = Min−7 and Max_b = Max + 7 obtained by the Min / Max changing unit 104. Then, the γ conversion unit 108 performs gradation conversion according to the input luminance data, and outputs the data after γ conversion.

  With the image processing apparatus having the above configuration, it is possible to reduce the problem that the dynamic γ processing suppresses the effects of undershoot and overshoot imparted by the enhancer. In addition, dynamic γ processing can be performed on a frame in which a histogram is detected without delay.

<Example 3>
FIG. 6 shows a block diagram of the image processing apparatus in this embodiment. This image processing apparatus includes a histogram detection unit 101, an enhancer intensity setting unit 102, a Min / Max detection unit 103, a gradation conversion curve creation unit 105, an IP conversion unit 106, an enhancer unit 107, a γ conversion unit 108, and a histogram LPF unit 301. It is composed of The same blocks as those in FIG. 1 used in Example 1 are denoted by the same reference numerals. The operation of this embodiment configured as described above will be described below.

  In the present embodiment, the enhancer strength setting unit 102 sets the enhancer strength G and outputs it to the histogram LPF unit 301 and the enhancer unit 107.

  The histogram LPF unit 301 applies an LPF (low-pass filter) to the histogram detected by the histogram detection unit 101. Here, it is known that the histogram after the enhancer process is expanded to the low gradation side and the high gradation side as shown in FIG. 7 because undershoot and overshoot are given to the edge portion. Note that the dotted line in FIG. 7 represents the histogram before the enhancer process, and the solid line represents the histogram after the enhancer process. In the present embodiment, the histogram detected by the histogram detection unit 101 is subjected to LPF by the histogram LPF unit 301 so that a histogram expanded to the low gradation side and the high gradation side is created. Can be predicted.

  As described above, the enhancer strength G is input from the enhancer strength setting unit 102 to the histogram LPF unit 301. Here, when the LPF coefficient is increased, the histogram is expanded to a wider range. Therefore, the LPF coefficient in the histogram LPF unit 301 is increased as the enhancer strength G output from the enhancer strength setting unit 102 increases.

  The Min / Max detection unit 103 detects the minimum luminance value Min and the maximum luminance value Max from the histogram output from the histogram LPF unit 301. The obtained Min and Max are values that have already been corrected by the LPF, and therefore the Min / Max changing unit 104 is not necessary in the present embodiment.

  The gradation conversion curve creation unit 105 creates a gradation conversion curve from Min and Max obtained by the Min / Max detection unit 103. The γ conversion unit 108 performs gradation conversion according to the input luminance data, and outputs data after γ conversion.

  In the image processing apparatus having the above configuration, it is possible to reduce the problem that the dynamic γ processing suppresses the effects of undershoot and overshoot imparted by the enhancer. In addition, dynamic γ processing can be performed on a frame in which a histogram is detected without delay.

1 is a block diagram of an image processing apparatus according to Embodiment 1. FIG. The table stored in the Min / Max change part of Example 1. FIG. 6 is a tone conversion curve created by the tone conversion curve creating unit according to the first embodiment. FIG. 4 is a block diagram of an image processing apparatus according to a second embodiment. The table stored in the Min / Max change part of Example 2. FIG. FIG. 9 is a block diagram of an image processing apparatus according to a third embodiment. The histogram before the enhancer process of Example 3, and after a process. A histogram obtained from the input video signal. Gradation conversion curve when performing γ conversion. FIG. 6 is a block diagram of an image processing apparatus that performs conventional dynamic γ processing. The figure explaining the signal processing of an enhancer process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Histogram detection part 102 Enhancer intensity | strength setting part 103 Min / Max detection part 104 Min / Max change part 105 Tone conversion curve creation part 106 IP conversion part 107 Enhancer part 108 γ conversion part 201 Edge intensity detection part 301 Histogram LPF part

Claims (9)

  Detecting means for detecting a minimum value and a maximum value of luminance values of pixels in an image included in the video signal;
  Creating means for creating a gradation conversion curve indicating the relationship between the input luminance value and the output luminance value in the gradation conversion based on the minimum value and the maximum value of the luminance values detected by the detecting means;
  Processing means for performing enhancer processing on the image according to enhancer strength indicating the strength of enhancer processing for enhancing the contour of the image;
  Gradation conversion means for performing gradation conversion on an image subjected to the enhancer processing by the processing means, using the gradation conversion curve created by the creation means;
Have
  The minimum and maximum luminance values detected by the detection means are changed according to the enhancer intensity,
  The creation means creates the gradation conversion curve using the changed minimum value and changed maximum value after the change.
An image processing apparatus.   The stronger the enhancer strength, the smaller the change minimum value with respect to the minimum value of the brightness value detected by the detection means, and the change maximum value is smaller than the maximum value of the brightness value detected by the detection means. growing
The image processing apparatus according to claim 1.   The minimum value and the maximum value of the luminance value detected by the detection means are changed according to the enhancer strength and the edge strength indicating the strength of the edge portion included in the image,
  The creation means creates the gradation conversion curve using the changed minimum value and the changed maximum value after the change.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus.   The detection means creates a histogram from luminance values of an image included in the video signal, and detects the minimum value and the maximum value.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus.   IP conversion means for performing IP conversion on the video signal,
  The processing means performs an enhancer process on the video signal subjected to IP conversion by the IP conversion means.
The image processing apparatus according to claim 1.   First detection means for detecting a histogram from luminance values of pixels in an image included in the video signal;
  Correction means for correcting the histogram detected by the first detection means with a low-pass filter;
  Second detection means for detecting a minimum value and a maximum value of luminance values in the histogram corrected by the low-pass filter by the correction means;
  Creating means for creating a gradation conversion curve indicating a relationship between an input luminance value and an output luminance value in gradation conversion based on the minimum value and the maximum value detected by the second detection means;
  Processing means for performing enhancer processing on the image according to enhancer strength indicating the strength of enhancer processing for enhancing the contour of the image;
  Gradation conversion means for performing gradation conversion on an image subjected to the enhancer processing by the processing means, using the gradation conversion curve created by the creation means;
An image processing apparatus comprising:   The coefficient of the low-pass filter increases as the enhancer strength increases.
The image processing apparatus according to claim 6.   A detecting step for detecting a minimum value and a maximum value of luminance values of pixels in an image included in the video signal;
  A creating step for creating a gradation conversion curve indicating a relationship between an input luminance value and an output luminance value in the gradation conversion based on the minimum value and the maximum value of the luminance value detected in the detection step;
  A processing step of performing an enhancer process on the image according to an enhancer intensity indicating an intensity of an enhancer process that enhances an outline of the image;
  A gradation conversion step in which gradation conversion means performs gradation conversion on the image subjected to the enhancer processing by the processing step using the gradation conversion curve created in the creation step;
Have
  The minimum and maximum luminance values detected in the detection step are changed according to the enhancer intensity,
  In the creation step, the gradation conversion curve is created using the changed minimum value and the changed maximum value after the change.
An image processing method.   A first detection step in which a first detection means detects a histogram from luminance values of pixels in an image included in the video signal;
  A correction step in which the correction means corrects the histogram detected in the first detection step with a low-pass filter;
  A second detecting step for detecting a minimum value and a maximum value of the luminance value in the histogram corrected by the low-pass filter in the correcting step;
  A creation step for creating a gradation conversion curve indicating a relationship between an input luminance value and an output luminance value in gradation conversion based on the minimum value and the maximum value detected in the second detection step;
  A processing step of performing an enhancer process on the image according to an enhancer intensity indicating an intensity of an enhancer process that enhances an outline of the image;
  A gradation conversion unit that performs gradation conversion on the image that has undergone the enhancer processing in the processing step using the gradation conversion curve created in the creation step.
Tep,
An image processing method comprising:

Images