Gradation correction device for video luminance signal

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to controlling the gradation of a video luminance signal in a video device (International Patent Classification H04N5 / 16).

【0002】

[Conventional technology]

In recent years, a gradation correction device for an image luminance signal is known as described in Japanese Patent Application Laid-Open No. 4-265075.

【0003】

FIG. 20 shows a block diagram of a conventional image luminance signal gradation correction device. In FIG. 20, 101 is an input video brightness signal, 102 is an average image level (average brightness level), 103 is an output video brightness signal, 104 is a black extension amplifier, 105 is a black extension level control circuit, 106 is a black detection circuit, and 107 is. The gain control amplifier, 108 is a black-pedestal comparison circuit, 109 is a black peak hold circuit, and 110 is an average image level detection circuit.

【0004】

The operation of the conventional video luminance signal gradation correction device configured as described above will be described below.

【0005】

First, the black detection circuit 106 detects the black level (corresponding to the minimum value of the present invention) of the input video luminance signal. If this black level is larger than the pedestal level, the gain of the gain control amplifier 107 is increased and the gain of the black extension amplifier 104 is increased by the black extension level control circuit 105, and the gradation of the relatively dark part of the image is extended in the black direction. The gradation is corrected by the thing. The black level of the gradation-corrected output video brightness signal 103 is detected by the black peak hold circuit 109, compared by the black-pedestal comparison circuit 108, and the gain of the gain control amplifier is adjusted so that the correction result does not fall below the pedestal. At the same time, the average image level detection circuit 110 is configured to control the gain of the black extension amplifier according to the average brightness level to realize more optimum black level gradation correction.

【0006】

[Problems to be Solved by the Invention]

In this video luminance signal gradation correction device, in order to detect only the black level (minimum value) of the video luminance signal and correct only the gradation of the dark portion of the video luminance signal, the bright portion of the video luminance signal. In addition, there is a problem that the overall contrast cannot be improved, and improvement for this problem is required.

【0007】

[Means for solving problems]

In order to solve this problem, the present invention takes a video luminance signal as an input, detects both the minimum value and the maximum value during the effective video period, and the gradation of the input luminance signal from the difference between the maximum value and the minimum value. By determining a coefficient for correcting the above and applying the coefficient to the input video luminance signal, an output luminance signal is obtained and gradation correction is performed.

【0008】

As a result, it is possible to perform overall gradation correction from a bright portion and a bright portion to a dark portion of the image luminance signal, and it is possible to obtain a more effective gradation correction effect.

【0009】

BEST MODE FOR CARRYING OUT THE INVENTION

The invention according to claim 1 of the present invention takes a video luminance signal as an input, detects the minimum value and the maximum value during the effective video period, and determines the gradation of the input luminance signal from the difference between the maximum value and the minimum value. The image luminance signal is a gradation correction device configured to obtain an output luminance signal and perform gradation correction by determining a coefficient to be corrected and applying the coefficient to the input video luminance signal. The dynamic range of the output luminance signal is effective by detecting the minimum and maximum values of the luminance signal and assigning the minimum value to the blackest level of the output video luminance signal and the maximum value to the whitest level of the output luminance signal. It has the effect of expanding to and improving the contrast.

【0010】

The invention according to claim 2 is a sample window generation circuit that generates a window that detects the minimum value and the maximum value of the video brightness signal, a minimum value detection circuit that detects the minimum value in the sample window, and a sample window. A maximum value detection circuit that detects the maximum value, a first subtraction circuit that subtracts the minimum value from the maximum value, and a division circuit that uses this subtraction result as the denominator and inputs a predetermined constant value to the molecule. , A second subtraction circuit that subtracts the minimum value from the input brightness signal, a negative limit circuit that limits the negative value of this subtraction result to zero, and a multiplication circuit that multiplies the output of this limit circuit by the output of the division circuit. This is a video brightness signal gradation correction device provided with a limit circuit to prevent the multiplication result from overflowing. It detects the minimum and maximum values of the video brightness signal and outputs the minimum value to the output video brightness signal. The blackest level and the maximum value of are assigned to the whitest level of the output video brightness signal, the gradation correction coefficient between them is obtained by the first subtraction circuit and division circuit, and the dynamic range of the output brightness signal is calculated by the multiplication circuit. It has the effect of effectively correcting and enlarging and improving the contrast. At this time, it also has an effect that it can be limited by the second subtraction circuit, the negative limit circuit, and the limit circuit so as not to exceed the dynamic range.

【0011】

The invention according to claim 3 stabilizes the correction process by providing a smoothing filter for the vertical video signal period on the value at which the minimum value is detected and treating the output of this filter as a new minimum value. The video luminance signal gradation correction device according to claim 1, wherein the gradation correction device is characterized by the above-mentioned effect, and has an effect of stabilizing the gradation correction process by passing the minimum value through a smoothing filter.

【0012】

The invention according to claim 4 stabilizes the correction process by providing a smoothing filter for the vertical video signal cycle on the value at which the maximum value is detected and treating the output of this filter as a new maximum value. The video luminance signal gradation correction device according to claim 1, wherein the gradation correction device is characterized by the above-mentioned effect, and has an effect of stabilizing the gradation correction process by passing the maximum value through a smoothing filter.

【0013】

The invention according to claim 5 has an effect of gradation correction by providing an addition / subtraction circuit for adding / subtracting a constant value to a value at which a minimum value is detected and treating the output of the addition / subtraction circuit as a new minimum value. The video luminance signal gradation correction device according to claim 1, wherein the amount can be adjusted. The black side of the video luminance signal is obtained by adding or subtracting a constant value to the detected minimum value. It has the effect of being able to adjust the correction effect of.

【0014】

The invention according to claim 6 provides an addition / subtraction circuit for adding / subtracting a constant value to the value at which the maximum value is detected, and treats the output of the addition / subtraction circuit as a new maximum value to have an effect of gradation correction. The video luminance signal gradation correction device according to claim 1, wherein the amount can be adjusted. The white side of the video luminance signal is obtained by adding or subtracting a constant value to the maximum detected value. It has the effect of being able to adjust the correction effect of.

【0015】

The invention according to claim 7 is provided with an average luminance level detection circuit for detecting the average luminance level of the input video luminance signal, and an addition / subtraction circuit for changing a constant value according to claim 5 at this average luminance level. The image luminance signal gradation correction device according to claim 5, wherein the effect of the gradation correction is adjusted according to the average luminance level, and the black side is determined by the average luminance level of the input luminance signal. It has an effect that the gradation correction effect of the above can be further adjusted according to the average luminance level of the image.

【0016】

The invention according to claim 8 is provided with an average luminance level detection circuit for detecting the average luminance level of the input video luminance signal, and an addition / subtraction circuit for changing a constant value according to claim 6 at this average luminance level. The image luminance signal gradation correction device according to claim 6, wherein the effect of the gradation correction is adjusted according to the average luminance level, and the white side is determined by the average luminance level of the input luminance signal. It has an effect that the gradation correction effect of the above can be further adjusted according to the average luminance level of the image.

【0017】

The invention according to claim 9 is provided with a minimum value selection circuit in which this value and a preset limit value are input to the value at which the minimum value is detected, and the smaller value is output as a new minimum value. The gradation correction device for the video brightness signal according to claim 1, wherein the effect of the gradation correction is limited, and the value is equal to or higher than a certain value with respect to the detected minimum value. By limiting the gradation so that it does not become excessive, it has an effect that excessive gradation can be prevented and more natural gradation correction can be performed.

【0018】

The invention according to claim 10 is provided with a maximum value selection circuit in which this value and a preset limit value are input to the value at which the maximum value is detected, and the larger value is output as a new maximum value. The gradation correction device for the video brightness signal according to claim 1, wherein the effect of the gradation correction is limited, and the value is less than or equal to a certain value with respect to the detected maximum value. By limiting the gradation so that it does not become excessive, it has an effect that excessive gradation can be prevented and more natural gradation correction can be performed.

【0019】

The invention according to claim 11 is provided with an average luminance level detection circuit for detecting the average luminance level of the input video luminance signal, and an addition / subtraction circuit for changing the limit value according to claim 9 at this average luminance level. The image luminance signal gradation correction device according to claim 9, wherein the effect of gradation correction is adjusted by changing the limit level of the minimum value according to the average brightness level. By correcting the limit value that limits the detected minimum value so that it does not exceed a certain value by the average brightness level of the video brightness signal, the floor is adjusted according to the average brightness level of the input video brightness signal. It has the effect of preventing excessive tone extension and performing more natural gradation correction.

【0020】

The invention according to claim 12 is provided with an average luminance level detection circuit for detecting the average luminance level of the input video luminance signal, and an addition / subtraction circuit for changing the limit value according to claim 10 at this average luminance level. The image luminance signal gradation correction device according to claim 10, wherein the effect of gradation correction is adjusted by changing the limit level of the maximum value according to the average brightness level. By correcting the limit value that limits the maximum value detected so that it does not fall below a certain value, the average brightness level of the video brightness signal is adjusted according to the average brightness level of the input video brightness signal. It has the effect of preventing excessive tone extension and performing more natural gradation correction.

【0021】

The invention according to claim 13 limits the effect of gradation correction by inputting a correction coefficient determined by a correction coefficient determination circuit and a preset limit value and limiting the correction coefficient to a limit value or less. The image brightness signal gradation correction device according to claim 1, wherein the gradation correction device is used, and when the value of the determined correction coefficient is large and the amount of gradation extension is large, the correction is performed. By limiting the coefficient by the limit value, the correction effect can be limited, and more natural gradation correction can be performed.

【0022】

The invention according to claim 14 is provided with an average luminance level detection circuit for detecting the average luminance level of the input video luminance signal, and an addition / subtraction circuit for changing the limit value according to claim 13 at this average luminance level. The image luminance signal gradation correction device according to claim 13, wherein the effect of gradation correction is adjusted by changing the limit level of the limit circuit according to the average brightness level. When the value of the corrected correction coefficient is large and the amount of extension of gradation is large, the correction coefficient is limited by the limit value according to the average brightness level of the input video luminance signal, so that the floor is more natural. It has the effect of being able to perform adjustment.

【0023】

The invention according to claim 15 is a sample window generation circuit that receives a horizontal synchronization signal and a vertical synchronization signal of an input video brightness signal as inputs and generates a window for detecting the minimum value and the maximum value of the video brightness signal, and a sample window. A minimum value detection circuit that detects the minimum value, a first smoothing filter that smoothes the minimum value with a vertical video signal cycle, and a first that adds or subtracts a first constant value to the output of this filter. Addition / subtraction circuit, minimum value selection circuit that limits the output of this first addition / subtraction circuit to less than or equal to the preset first limit value, maximum value detection circuit that detects the maximum value in the sample window, and this maximum A second smoothing filter that smoothes the value with a vertical video signal cycle, a second addition / subtraction circuit that adds / subtracts a second constant value to the output of this filter, and the output of this second addition / subtraction circuit are pre-populated. The maximum value selection circuit that limits to the set second limit value or higher, the first subtraction circuit that subtracts the output of the minimum value selection circuit from the output of the maximum value selection circuit, and the subtraction result as the denominator are used in advance in the molecule. The first division circuit that inputs a predetermined third constant value is compared with the output of this division circuit and the preset third limit value, and the output value of the division circuit is limited to the third limit value or less. The limit circuit of, the second subtraction circuit that subtracts the output of the minimum value selection circuit from the input brightness signal, the negative side limit circuit that limits the negative value of this subtraction result to zero, and the output of this negative side limit circuit. This is a sample window generation circuit that is provided with a multiplication circuit that multiplies the output of the first limit circuit and a second limit circuit that prevents the multiplication result from overflowing. Allows the maximum and minimum values of any range of the image to be detected, and the smoothing filter can stabilize the processing. First and second addition / subtraction circuits, maximum value selection circuit, minimum value selection circuit, and first limit circuit. The correction effect can be adjusted by, and the negative side limit circuit and the second limit circuit have the effect of preventing the dynamic range from being exceeded.

【0024】

The invention according to claim 16 provides an average brightness level detection circuit for detecting the average brightness level in the sample window output from the sample window generation circuit among the input video brightness signals, and obtains the average brightness level detected by the average brightness level detection circuit. A first gain control circuit for gain control, a second gain control circuit for gain control of the average brightness level, a third gain control circuit for gain control of the average brightness level, and a fourth gain control circuit for gain control of the average brightness level. The first constant value is added to or subtracted from the output of the gain control circuit of, the fifth gain control circuit that gain-controls the average brightness level, and the first gain control circuit, and the result is converted to a new first constant value. A first addition / subtraction circuit that replaces and outputs, and a second addition / subtraction circuit that adds / subtracts a second constant value to the output of the second gain control circuit and replaces the result with a new second constant value for output. , Add or subtract the first limit value to the output of the third gain control circuit, replace this result with the new first limit value and output it to the output of the third gain control circuit and the output of the fourth gain control circuit. The second limit value is added / subtracted, the result is replaced with a new second limit value and output, and the third limit value is added / subtracted to the output of the fifth gain control circuit. It is equipped with a fifth addition / subtraction circuit that replaces the result with a new third limit value and outputs it, and is characterized by controlling the correction effect of gradation correction according to the average brightness level of the input video brightness signal. The image brightness signal gradation correction device according to claim 15 is used, and each effect control value (constant value, limit value) according to claim 15 is adjusted according to the average brightness level of the input video brightness signal. By doing so, it has the effect of being able to perform more natural gradation correction.

【0025】

The invention according to claim 17 is a pedestal level detection circuit that detects a pedestal level of a video signal, a comparison circuit that compares the pedestal level and the level of an input video luminance signal based on the pedestal level detection result, and a comparison thereof. As a result, the video luminance signal according to claim 2, wherein when the input video luminance signal is smaller than the pedestal level, the gradation correction is stopped to prevent the synchronous signal from being subjected to the gradation correction. When the input video luminance signal is below the pedestal level, that is, in the video synchronization signal portion, the effect on the synchronization signal can be eliminated by eliminating the gradation correction effect of the present invention. It has the effect of being able to do it.

【0026】

The invention according to claim 18 is provided with a pedestal level detection circuit for detecting the pedestal level of the video signal and an addition circuit for adding the detected pedestal level to the output video luminance signal, and the pedestal level before and after gradation correction. The video luminance signal gradation correction device according to claim 2, wherein the pedestal level of the input video luminance signal and the pedestal level of the output video luminance signal can be made the same. It has the effect of.

【0027】

(Embodiment 1) Hereinafter, the embodiment of the invention described in claim 1 of the present invention will be described with reference to FIGS. 1 and 2.

【0028】

FIG. 1 is a block diagram of the present invention, FIG. 2 shows the input / output characteristics of the gradation correction device of the present invention, and in FIG. 1, 1 is a minimum value detection circuit for each field or frame of the input video luminance signal a. Detect the minimum value of. 2 is a maximum value detection circuit that detects the maximum value of the input video luminance signal a in each field or frame unit. 3 is a subtraction circuit that subtracts the minimum value b from the maximum value c and outputs the luminance distribution amount d. 4 is a correction coefficient determination circuit, which determines the correction coefficient e, which is the correction amount of the input video luminance signal a, from the luminance distribution amount d by calculation. In 5 is a correction circuit, the output video luminance signal f is obtained by applying the correction coefficient e to the input video luminance signal a. In FIG. 2, the slope of the straight line connecting the detected minimum and maximum values is the correction coefficient e. By multiplying the input video luminance signal a by this correction coefficient e, it is converted into an output video luminance signal f and gradation correction is performed.

【0029】

(Embodiment 2) Next, the embodiment of the invention described in claim 2 of the present invention will be described with reference to FIGS. 3 and 2.

【0030】

FIG. 3 shows a block diagram of the present invention. In FIG. 3, 1 to 3 have the same configuration as that of the first embodiment, 6 is a division circuit in which the luminance distribution amount d is used as the denominator and a constant value r is used as the numerator. Input and output the correction coefficient e. This constant value r corresponds to the maximum luminance level of the output video luminance signal. For example, when the output video luminance signal is 8 bits, 256 (decimal number) or the like is given. Reference numeral 7 denotes a sample window generation circuit that inputs a horizontal synchronization signal k and a vertical synchronization signal l, and a counter circuit can generate a desired sampling window g for which the maximum value and the minimum value are to be detected. 8 is the second subtraction circuit, which subtracts the minimum value b from the input video luminance signal a and outputs the subtracted video luminance signal h. Reference numeral 9 limits the non-subtractive portion of the subtracted video luminance signal h obtained by the second subtraction circuit, that is, the portion of the input video luminance signal a below the minimum value b to zero, and outputs the corrected video luminance signal i. 10 is a multiplication circuit that multiplies the corrected video luminance signal i by the correction coefficient e and outputs the multiplied video luminance signal j. Reference numeral 11 denotes a limit circuit, which limits the amplitude of the multiplied video luminance signal j so as not to exceed the dynamic range. With the above configuration, the gradation correction that has the input / output characteristics as shown in FIG. 2 is realized.

【0031】

(Embodiment 3) Next, the embodiment of the invention described in claim 3 of the present invention will be described with reference to FIG.

【0032】

FIG. 4 shows a block diagram of the present invention, and FIGS. 4 to 5 have the same configuration as that of the first embodiment. Reference numeral 12 denotes a smoothing filter, which performs cyclic filtering or average value filtering of the vertical video signal period (field or frame period) for the minimum value b, and processes by smoothly smoothing the fluctuation of the minimum value in the vertical video signal period. It is configured to stabilize.

【0033】

(Embodiment 4) Next, the embodiment of the invention described in claim 4 of the present invention will be described with reference to FIG.

【0034】

FIG. 5 shows a block diagram of the present invention, and FIGS. 5 to 5 have the same configuration as that of the first embodiment. Reference numeral 12 denotes a smoothing filter, which performs cyclic filtering or average value filtering of the vertical video signal period (field or frame period) for the maximum value b, and processes by smoothly smoothing the fluctuation of the maximum value in the vertical video signal period. It is configured to stabilize.

【0035】

(Embodiment 5) Next, the embodiment of the invention described in claim 5 of the present invention will be described with reference to FIGS. 6 and 2.

【0036】

FIG. 6 shows a block diagram of the present invention, and FIGS. 6 to 5 have the same configuration as that of the first embodiment. 13 is the effect of gradation correction by moving the position of the minimum value shown in Fig. 2 by adding or subtracting the preset constant value m to the minimum value b in the addition / subtraction circuit and setting it as the new minimum value b'. Is configured to control.

【0037】

(Embodiment 6) Next, the embodiment of the invention described in claim 6 of the present invention will be described with reference to FIGS. 7 and 2.

【0038】

FIG. 7 shows a block diagram of the present invention, and FIGS. 7 to 5 have the same configuration as that of the first embodiment. 13 is the effect of gradation correction by moving the position of the maximum value shown in Fig. 2 by adding or subtracting a preset constant value m to the maximum value c in the addition / subtraction circuit and setting it as the new minimum value c'. Is configured to control.

【0039】

(Embodiment 7) Next, the embodiment of the invention described in claim 7 of the present invention will be described with reference to FIGS. 8 and 2.

【0040】

FIG. 8 shows a block diagram of the present invention, and FIGS. 8 to 5 and 13 have the same configuration as that of the fifth embodiment. Reference numeral 14 denotes an average luminance level detection circuit that detects and outputs the average luminance level n of the input video luminance signal a. 15 adds or subtracts the average luminance level to the constant value m preset by the addition / subtraction circuit, and outputs the average luminance level correction constant value m'. By processing this m'in the same manner as the constant value of the fifth embodiment, a new minimum value b'can be obtained according to the average luminance level n, and the minimum value shown in FIG. 2 according to the average luminance level. It is configured to control the effect of gradation correction by moving the position of.

【0041】

(Embodiment 8) Next, the embodiment of the invention described in claim 8 of the present invention will be described with reference to FIGS. 9 and 2.

【0042】

FIG. 9 shows a block diagram of the present invention, and FIGS. 9 to 5 and 13 have the same configuration as that of the sixth embodiment. Reference numeral 14 denotes an average luminance level detection circuit that detects and outputs the average luminance level n of the input video luminance signal a. 15 adds or subtracts the average luminance level to the constant value m preset by the addition / subtraction circuit, and outputs the average luminance level correction constant value m'. By processing this m'in the same manner as the constant value of the sixth embodiment, a new maximum value c'can be obtained according to the average luminance level n, and the maximum value shown in FIG. 2 according to the average luminance level. It is configured to control the effect of gradation correction by moving the position of.

【0043】

(Embodiment 9) Next, the embodiment of the invention described in claim 9 of the present invention will be described with reference to FIGS. 10 and 2.

【0044】

FIG. 10 shows a block diagram of the present invention, and FIGS. 10 to 5 have the same configuration as that of the first embodiment. 16 compares the minimum value b with the preset limit value o in the minimum value selection circuit, limits the minimum value so that the minimum value b does not become larger than the limit value o, and sets it as the new minimum value b'. By outputting, the effect of gradation correction is limited by limiting the position of the minimum value shown in FIG. 2 so as not to go too far to the right.

【0045】

(Embodiment 10) Next, the embodiment of the invention described in claim 10 of the present invention will be described with reference to FIGS. 11 and 2.

【0046】

FIG. 11 shows a block diagram of the present invention, and FIGS. 11 to 5 have the same configuration as that of the first embodiment. 17 compares the maximum value c with the preset limit value p in the maximum value selection circuit, limits the maximum value so that the maximum value c does not become larger than the limit value p, and sets it as the new minimum value c'. By outputting, the effect of gradation correction is limited by limiting the position of the maximum value shown in FIG. 2 so as not to go too far to the left.

【0047】

(Embodiment 11) Next, the embodiment of the invention described in claim 11 of the present invention will be described with reference to FIGS. 12 and 2.

【0048】

FIG. 12 shows a block diagram of the present invention, and FIGS. 12 to 5 and 16 have the same configuration as that of the ninth embodiment. Reference numeral 14 denotes an average luminance level detection circuit, which has the same configuration as that of the seventh embodiment. 18 is an addition / subtraction circuit that adds / subtracts the average luminance level m and the preset limit value o and gives it to the minimum value selection circuit 16 as a new limit value o'so that the minimum value b does not become larger than the limit value o'. By limiting the minimum value and outputting it as a new minimum value b', gradation correction is performed by limiting the position of the minimum value shown in Fig. 2 according to the average brightness level so that it does not go too far to the right. It is configured to limit the effect of.

【0049】

(Embodiment 12) Next, the embodiment of the invention described in claim 12 of the present invention will be described with reference to FIGS. 13 and 2.

【0050】

FIG. 13 shows a block diagram of the present invention, and FIGS. 13 to 5 and 17 have the same configuration as that of the tenth embodiment. Reference numeral 14 denotes an average luminance level detection circuit, which has the same configuration as that of the seventh embodiment. 19 is an addition / subtraction circuit that adds / subtracts the average luminance level m and the preset limit value p and gives it to the maximum value selection circuit 17 as a new limit value p'so that the maximum value c does not become larger than the limit value p'. By limiting the maximum value and outputting it as a new maximum value c', gradation correction is performed by limiting the position of the maximum value shown in Fig. 2 according to the average brightness level so that it does not go too far to the left. It is configured to limit the effect of.

【0051】

(Embodiment 13) Next, the embodiment of the invention described in claim 13 of the present invention will be described with reference to FIGS. 14 and 2.

【0052】

FIG. 14 shows a block diagram of the present invention, and FIGS. 14 to 5 have the same configuration as that of the first embodiment. 23 compares the limit value q preset in the limit circuit with the correction coefficient e, limits the correction coefficient e so that it does not become larger than the limit value q, and then outputs it as a new correction coefficient e'to perform gradation correction. The effect of gradation correction is limited by limiting the input / output characteristics so that the slope of the input / output characteristics shown in FIG. 2 does not become too steep.

【0053】

(Embodiment 14) Next, the embodiment of the invention described in claim 14 of the present invention will be described with reference to FIGS. 15 and 2.

【0054】

FIG. 15 shows a block diagram of the present invention, and FIGS. 15 to 5 have the same configuration as that of the first embodiment. Further, 23 is a limit circuit having the same configuration as that of the thirteenth embodiment. Further, reference numeral 14 denotes an average luminance level detection circuit, which has the same configuration as that of the seventh embodiment. 20 adds / subtracts the preset limit value q and the average luminance level m in the addition / subtraction circuit, and outputs a new limit value q'. The limit circuit 23 compares the new limit value q'and the correction coefficient e, limits the correction coefficient e so that it does not become larger than the limit value q', and then outputs the new correction coefficient e'to perform gradation correction. As a result, the effect of gradation correction is limited by limiting according to the average luminance level so that the slope of the input / output characteristics shown in FIG. 2 does not become too steep.

【0055】

(Embodiment 15) Next, the embodiment of the invention described in claim 15 of the present invention will be described with reference to FIG.

【0056】

FIG. 16 shows a block diagram of the present invention, and FIGS. 16 to 5 have the same configuration as that of the first embodiment. Further, 6 to 11 have the same configuration as that of the second embodiment. Further, 12 has the same configuration as that of the third embodiment. Reference numeral 21 denotes a smoothing filter, which has the same configuration as the smoothing filter of the fourth embodiment. 13 has the same configuration as that of the fifth embodiment. Reference numeral 22 denotes an addition / subtraction circuit, which has the same configuration as the addition / subtraction circuit of the sixth embodiment. 16 has the same configuration as that of the ninth embodiment. 17 has the same configuration as that of the tenth embodiment. 23 has the same configuration as that of the thirteenth embodiment. With the above configuration, it is possible to realize a gradation correction device that has stable processing, is smooth, and can arbitrarily set the effect of gradation correction.

【0057】

(Embodiment 16) Next, the embodiment of the invention described in claim 16 of the present invention will be described with reference to FIG.

【0058】

FIG. 17 shows a block diagram of the present invention, and FIGS. 17 to 13 and 21 to 23 have the same configuration as that of the fifteenth embodiment. Reference numeral 14 denotes an average luminance level detection circuit, which has the same configuration as that of the seventh embodiment. Reference numeral 24 denotes a first gain control circuit, which controls the gain of the average luminance level n and adds or subtracts it to the second constant value s by the third addition / subtraction circuit 32 to obtain a new second constant value s'. Let it be the addition / subtraction value of the second addition / subtraction circuit 22. Further, 25 is a second gain control circuit, which controls the gain of the average luminance level n and adds or subtracts it to the first constant value m by the fourth addition / subtraction circuit 33 to obtain a new first constant value m'. This is used as the addition / subtraction value of the first addition / subtraction circuit 13. Reference numeral 26 denotes a third gain control circuit, which controls the gain of the average luminance level n and adds or subtracts it to the second limit value o by the fifth addition / subtraction circuit 34 to obtain a new second limit value o'. The limit value of the maximum value selection circuit 17 is used. Reference numeral 27 denotes a fourth gain control circuit, which controls the gain of the average luminance level n and adds / subtracts this to the first limit value p in the sixth addition / subtraction circuit 35 to obtain a new first limit value p'. The limit value of the minimum value selection circuit 16 is used. Reference numeral 37 denotes a fifth gain control circuit, which controls the gain of the average luminance level n and adds / subtracts this to the third limit value q in the seventh addition / subtraction circuit 36 to obtain a new third limit value q'. It is the limit value of the first limit circuit 23. With the above configuration, it is possible to realize a gradation correction device that has stable processing, is smooth, and can arbitrarily set the effect of gradation correction according to the average luminance level.

【0059】

(Embodiment 17) Next, the embodiment of the invention described in claim 17 of the present invention will be described with reference to FIG.

【0060】

FIG. 18 shows a block diagram of the present invention, and in FIG. 18, the configurations 1 to 3 and 6 to 11 are the same as those of the second embodiment. 28 is a pedestal level detection circuit that detects the brightness level of the back pouch or front pouch part of the input video brightness signal a and outputs the pedestal level u. Reference numeral 29 denotes a comparison circuit, which compares the input video luminance signal a with the pedestal level u and outputs a determination signal v indicating whether the input video luminance signal a is equal to or less than the pedestal. 30 is a correction stop circuit, and when the judgment signal v is equal to or less than the pedestal, the correction coefficient e is switched to the correction stop state. This makes it possible to prevent side effects on performing gradation correction on the synchronized signal.

【0061】

(Embodiment 18) Next, the embodiment of the invention described in claim 18 of the present invention will be described with reference to FIG.

【0062】

FIG. 19 shows a block diagram of the present invention, and in FIG. 19, the configurations of 1 to 3 and 6 to 11 are the same as those of the second embodiment. 28 has the same configuration as that of the 17th embodiment. 31 is an adder circuit that adds a pedestal level u to the corrected output luminance signal f to output a corrected output luminance signal w having the same pedestal level as the input video luminance signal. 38 is a third limit circuit that prevents overflow in the addition circuit 31 and outputs the output video luminance signal x. As a result, a gradation correction device having the same input and output pedestal levels can be realized.

【0063】

[Effect of the invention]

As described above, according to the present invention, it is possible to perform overall gradation correction from a bright portion and a bright portion to a dark portion of an image luminance signal, thereby obtaining a more effective gradation correction effect. It is possible to prevent the gradation correction from being applied to the synchronization signal portion of the video, and to obtain an advantageous effect that the gradation correction having the same input / output pedestal level can be realized.

[Simple explanation of drawings]

[Figure 1]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Figure 2]

Input / output characteristic diagram of the gradation correction device for the same video luminance signal [Fig. 3]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 4]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 5]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 6]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 7]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 8]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 9]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 10]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 11]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 12]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 13]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 14]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 15]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 16]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 17]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 18]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 19]

Block configuration diagram of a gradation correction device for an image luminance signal according to an embodiment of the present invention [Fig. 20]

Block configuration diagram of a conventional video luminance signal gradation correction device [Explanation of symbols]

1 Minimum value detection circuit 2 Maximum value detection circuit 3 Subtraction circuit 4 Correction coefficient determination circuit 5 Correction circuit 6 Division circuit 7 Sample window detection circuit 8 Subtraction circuit 9 Negative side limit circuit 10 multiplication circuit 11 Limit circuit 12 Smoothing filter 13 Addition / subtraction circuit 14 Average brightness level detection circuit 15 Addition / subtraction circuit 16 Minimum value selection circuit 17 Maximum value selection circuit 18 Addition / subtraction circuit 19 Addition / subtraction circuit 20 Addition / subtraction circuit 21 Smoothing filter 22 Addition / subtraction circuit 23 Limit circuit 24 Gain control circuit 25 Gain control circuit 26 Gain control circuit 27 Gain control circuit 28 Pedestal level detection circuit 29 Comparison circuit 30 Compensation stop circuit 31 Addition circuit 32 Addition / subtraction circuit 33 Addition / subtraction circuit 34 Addition / subtraction circuit 35 Addition / subtraction circuit 36 Addition / subtraction circuit 37 Gain control circuit 104 Black extension amplifier 105 Black extension level control circuit 106 Black detection circuit 107 Gain control amplifier 108 Black-pedestal comparison circuit 109 Black peak hold circuit 110 Average image level detection circuit