JP2006033226A - Gradation correcting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gradation correcting circuit capable of providing high contrast to primary color signals, without losing brightness in appearance. <P>SOLUTION: A gradation information calculation circuit 101 calculates a luminance signal Y from the primary color signals, a luminance distribution extract circuit 102 generates a normalized cumulative frequency distribution HST, and a gradation correction conversion table generating circuit 104 generates a correction amount ΔY. Signal selection circuits 107 to 109 output a red selection signal SR, a green selection signal SG, and a blue selection signal SB, on the basis of a value of a correction rate of change YK from a correction change rate calculation circuit 105; multiplier circuits 110 to 112 multiply the signals with the correction rate of change YK, respectively to output a red multiplication signal MR, a green multiplication signal MG, and a blue multiplication signal MB; and adder circuits 113 to 115 respectively add a red primary color signal RI, a green primary color signal GI and a blue primary color signal BI to them to output primary color signals RO, GO and BO. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gradation correction apparatus that corrects the gradation of a video signal.

  Various display quality enhancement technologies have been proposed and put into practical use in display devices that perform gradation display in a digital manner, such as plasma display panels (hereinafter abbreviated as PDP) and liquid crystal display devices (hereinafter abbreviated as LCD). It has become. Among these image quality enhancement technologies, technologies relating to smoothing processing of the luminance distribution of video signals for realizing high contrast by effectively utilizing the gradation dynamic range of the display device have been proposed (for example, Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4). The smoothing process of the luminance distribution of the video signal is a process of correcting the video signal so as to smooth the luminance distribution of the video signal for one frame or one field, and the video is more clearly displayed on the display device. It is a technique for displaying on the screen. In such a luminance distribution smoothing process (hereinafter, also simply referred to as a smoothing process), it is possible to improve the contrast of an image or to brighten a dark image as a whole.

  FIG. 15 is a diagram comparing luminance distributions before and after the smoothing process according to the prior art. FIG. 15A is a diagram showing a frequency distribution of luminance for one frame before smoothing processing in a certain video signal, and FIG. 15B is 1 after smoothing processing by a conventional gradation correction device. It is a figure which shows the frequency distribution of the brightness | luminance for a flame | frame. 15A and 15B, the horizontal axis represents the brightness of the video signal (hereinafter abbreviated as the luminance level), and the vertical axis represents how many video areas of that luminance level exist in one frame. Appearance frequency (hereinafter abbreviated as frequency) is shown. In the example shown in FIG. 15A, the frequency is high around the middle of the luminance level. When smoothing processing is performed on the video signal shown in FIG. 15A, the luminance distribution is smoothed over the entire range of luminance levels as shown in FIG. 15B. As a result, in the video signal shown in FIG. 15B, darker and brighter portions are increased as compared with the video signal shown in FIG.

Generally, these smoothing processes are performed on the luminance signal. On the other hand, in a PDP or LCD, an image is displayed by three primary color signals of a red primary color signal, a green primary color signal, and a blue primary color signal. For this reason, in the conventional gradation correction device, the red primary color signal, the green primary color signal, and the blue primary color signal are once converted into luminance signals, and the luminance distribution is smoothed on the converted luminance signals. Then, the luminance signal before smoothing is compared with the luminance signal after smoothing to obtain the conversion ratio of the luminance signal, and the conversion ratio is multiplied by the red primary signal, green primary signal, and blue primary signal. Increase the contrast.
Japanese Unexamined Patent Publication No. 63-040472 JP 08-115417 A JP 2002-165095 A Japanese Patent Laid-Open No. 08-023460

  However, in the above-described gradation correction apparatus, the red primary color signal, the green primary color signal, and the blue primary color signal are multiplied by the same conversion ratio, so that the brightness level is reduced by the smoothing process as compared with that before the smoothing process. In an image area with a high luminance level, there is a problem that the absolute value of the difference between each of the red primary color signal, the green primary color signal, and the blue primary color signal becomes small. In such a case, colors with high visual sensitivity such as skin color may appear to be missing.

  An object of the present invention is to provide a gradation correction apparatus capable of increasing the contrast of a primary color signal so that the vividness of an appearance is not lost even for a color with high visual sensitivity.

  In order to achieve such an object, the gradation correction apparatus of the present invention includes a luminance correlation information generating unit that generates luminance correlation information having a correlation with luminance from a plurality of input primary color signals, and luminance correlation. Correction information generating means for generating correction information for smoothing the luminance distribution extracted based on the information, correction change rate calculating means for calculating the correction change rate based on the luminance correlation information and the correction information, Mixed signal generating means for generating a mixed signal having a correlation with all of the plurality of primary color signals input, and the plurality of input depending on whether the value of the correction change rate is a value greater than or equal to 0 The present invention is characterized in that correction is performed on the primary color signal.

  With this configuration, the primary color signal can be output with high contrast by gradation correction, and the change in color balance is suppressed in areas where the luminance level increases due to gradation correction, while saturation is reduced in areas where the luminance level decreases. High contrast can be realized while suppressing the decrease.

  Further, when the value of the correction change rate is smaller than 0, the multiplication signal is generated by multiplying the value of the correction change rate by the mixed signal of the mixed signal generating means, and this multiplied signal and a plurality of primary color signals inputted thereto A sum signal obtained by adding to may be output. According to such a configuration, it is possible to realize high contrast while suppressing a decrease in saturation in a region where the luminance level is lowered by gradation correction.

  Further, when the value of the correction change rate is a value equal to or greater than 0, a multiplication signal is generated by multiplying the value of the correction change rate and the input primary color signals, and the multiplication signal and the input primary colors An addition signal obtained by adding the signals may be output. According to such a configuration, it is possible to realize high contrast while suppressing a change in color balance in an area where the luminance level is increased by gradation correction.

  In addition, the correction information generation unit detects the distribution of the appearance frequency of each value of the luminance correlation information for each frame, and the correction stores the correction amount at each value as correction information based on the distribution of the appearance frequency An information storage unit, and a correction change rate corresponding to the luminance correlation information may be calculated based on the correction information read from the correction information storage unit. According to such a configuration, it is possible to create correction information and a correction change rate for tone correction based on the distribution of the appearance frequency of each value of the luminance correlation information.

  According to the present invention, even when the luminance signal after the smoothing process is smaller than the luminance signal before the smoothing process, the primary color signal is increased in contrast so that the vividness of the appearance is not lost. It becomes possible.

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

(First embodiment)
FIG. 1 is a block diagram showing a configuration of a gradation correction apparatus according to the first embodiment of the present invention. 1 includes a gradation information calculation circuit 101, correction information generation means 150, signal selection circuits 107, 108, 109, a correction change rate calculation circuit 105, a mixed signal calculation circuit 106, and multiplication circuits 110, 111, 112. And addition circuits 113, 114, and 115. The correction information generation unit 150 includes a luminance distribution extraction circuit 102, a signal selection circuit 103, and a gradation correction conversion table creation circuit 104. In FIG. 1, a red primary color signal RI, a green primary color signal GI, and a blue primary color signal BI are digital primary color signals, and the value of the red primary color signal RI indicates a red luminance level (gradation) and a green primary color signal. The GI value represents the green luminance level (gradation), and the blue primary color signal BI represents the blue luminance level (gradation).

  The gradation information calculation circuit 101 receives a red primary color signal RI, a green primary color signal GI, and a blue primary color signal BI. The gradation information calculation circuit 101 that is a luminance correlation information generation unit includes three multiplication circuits, and luminance correlation information having a correlation with luminance from the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI. As a result, the luminance signal Y is calculated. The gradation information calculation circuit 101 outputs the calculated luminance signal Y to the luminance distribution extraction circuit 102, the signal selection circuit 103, the correction change rate calculation circuit 105, and the mixed signal calculation circuit 106.

  The luminance distribution extraction circuit 102 performs a luminance distribution extraction process from the luminance signal Y, creates a normalized cumulative frequency distribution HST, and outputs it to the signal selection circuit 103. Details of the luminance distribution extraction circuit 102 will be described later.

  The signal selection circuit 103 displays the luminance signal Y during the vertical effective scanning period (period during which video is displayed), the normalized cumulative frequency distribution HST during the vertical blanking period (period during which no video is displayed), the vertical synchronization signal, etc. And output to the gradation correction conversion table creation circuit 104. Here, the vertical effective scanning period is a period for displaying an image in one vertical scanning period, and the vertical blanking period is a period provided for a CRT that displays an image by scanning with an electron beam. The period during which the electron beam returns from the vertical scanning end point to the vertical scanning start point in one vertical scanning period.

  The gradation correction conversion table creation circuit 104 in the correction information generation means 150 creates a gradation correction conversion table for smoothing processing based on the normalized cumulative frequency distribution HST in the vertical blanking period, The correction information is stored in a correction information storage means (not shown). In the vertical effective scanning period, a correction amount ΔY, which is correction information for smoothing the luminance distribution, is generated from the luminance signal Y using the gradation correction conversion table, and the correction amount ΔY is used as a correction change rate. Output to the calculation circuit 105. This correction amount ΔY will be described later.

  The correction change rate calculation circuit 105, which is a correction change rate calculation means, includes one division circuit and divides the correction amount ΔY by the luminance signal Y, thereby smoothing the luminance distribution for the three digital primary color signals. A correction change rate YK for processing is calculated. The correction change rate calculation circuit 105 outputs the correction change rate YK to the signal selection circuits 107, 108, and 109 and the multiplication circuits 110, 111, and 112.

  The mixed signal calculation circuit 106 receives a red primary color signal RI, a green primary color signal GI, a blue primary color signal BI, and a luminance signal Y. The mixed signal calculation circuit 106, which is a mixed signal generating means, converts all of the red primary color signal RI, the green primary color signal GI, the blue primary color signal BI, and the luminance signal Y to the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI. As a mixed signal that is a correlated signal, a red mixed signal BLR, a green mixed signal BLG, and a blue mixed signal BLB are generated. Then, the red mixed signal BLR is output to the signal selection circuit 107, the green mixed signal BLG is output to the signal selection circuit 108, and the blue mixed signal BLB is output to the signal selection circuit 109. A method for calculating the red mixed signal BLR, the green mixed signal BLG, and the blue mixed signal BLB will be described later.

  The signal selection circuit 107 receives the red primary color signal RI, the signal selection circuit 108 receives the green primary color signal GI, and the signal selection circuit 109 receives the blue primary color signal BI. The signal selection circuit 107 selects the red primary color signal RI when the correction change rate YK is a value greater than or equal to 0, and selects the red mixed signal BLR when the correction change rate YK is a value smaller than 0, thereby selecting the red color. The selection signal SR is output to the multiplication circuit 110. Further, the signal selection circuit 108 selects the green primary color signal GI when the correction change rate YK is a value equal to or greater than 0, and selects the green mixed signal BLG when the correction change rate YK is a value smaller than 0. The selection signal SG is output to the multiplication circuit 111. The signal selection circuit 109 selects the blue primary color signal BI when the correction change rate YK is a value equal to or greater than 0, and selects the blue mixed signal BLB when the correction change rate YK is a value smaller than 0, and The selection signal SB is output to the multiplication circuit 112.

  The multiplication circuit 110 multiplies the red selection signal SR and the correction change rate YK, and outputs the multiplication result to the addition circuit 113 as a red multiplication signal MR. The multiplication circuit 111 multiplies the green selection signal SG and the correction change rate YK, and outputs the multiplication result to the addition circuit 114 as a green multiplication signal MG. The multiplication circuit 112 multiplies the blue selection signal SB and the correction change rate YK, and outputs the multiplication result to the addition circuit 115 as a blue multiplication signal MB. Therefore, when the correction change rate YK is a value smaller than 0, that is, when the red mixed signal BLR, the green mixed signal BLG, and the blue mixed signal BLB are selected as the red selection signal SR, the green selection signal SG, and the blue selection signal SB, respectively, multiplication is performed. The circuits 110, 111, and 112 output a red multiplication signal MR, a green multiplication signal MG, and a blue multiplication signal MB, and the correction change rate YK is a value of 0 or more, that is, a red selection signal SR, a green selection signal SG, and a blue selection signal. When red primary color signal RI, green primary color signal GI, and blue primary color signal BI are selected as SB, red multiplication signal MR, green multiplication signal MG, and blue multiplication signal MB are output from multiplication circuits 110, 111, and 112, respectively. .

  Further, the red primary color signal RI is input to the adder circuit 113, the green primary color signal GI is input to the adder circuit 114, and the blue primary color signal BI is input to the adder circuit 115. Then, the adding circuit 113 adds the red primary color signal RI and the red multiplication signal MR, and outputs the addition result as a red primary color signal RO. The adder circuit 114 adds the green primary color signal GI and the green multiplication signal MG, and outputs the addition result as the green primary color signal GO. The adder circuit 115 adds the blue primary color signal BI and the blue multiplication signal MB, and outputs the addition result as the blue primary color signal BO. Therefore, when the correction change rate YK is a value smaller than 0, that is, when the red multiplication signal MR, the green multiplication signal MG, and the blue multiplication signal MB are output from the multiplication circuits 110, 111, and 112, the addition circuits 113, 114, and 115 A red primary color signal RO, a green primary color signal GO, and a blue primary color signal BO are output, and the correction change rate YK is a value of 0 or more, that is, the red multiplication signal MR, the green multiplication signal MG, and the blue multiplication signal from the multiplication circuits 110, 111, and 112. When MB is output, the adder circuits 113, 114, 115 output a red primary color signal RO, a green primary color signal GO, and a blue primary color signal BO.

  Next, the configuration and operation of the luminance distribution extraction circuit 102 in the correction information generation unit 150 will be described. FIG. 2 is a block diagram showing a configuration of the luminance distribution extraction circuit 102 of the gradation correction apparatus shown in FIG.

Luminance distribution extraction circuit 102 shown in FIG. 2, the address decoder 201, n number of counters _{202 1, 202 2, ····,} 202 n ( _hereinafter, abbreviated to 202 1 to 202 _n), the cumulative frequency distribution creating circuit 203, a gain control circuit 204 and a normalization circuit 205. Here, n represents the number of luminance levels (the number of gradations). For example, n is 256 when the luminance signal Y has 8 bits. Hereinafter, in the first embodiment of the present invention, description will be made assuming that n = 256, but the number of gradations is not limited to this, and can be set to an arbitrary value.

First, the luminance signal Y is input to the address decoder 201. The address decoder 201 outputs pulses P1 to Pn to any _{one of} the counters 202 ₁ to 202 _n according to the value of the luminance signal Y.

For example, the address decoder 201, when the luminance level of the luminance signal Y is 0 and outputs a pulse P1 to the counter 202 _1, and outputs a pulse P2 to the counter 202 ₂ when the value of the luminance signal Y is 1, When the value of the luminance signal Y is n−1, the pulse Pn is output to the counter 202 _n .

The counters 202 _{1 to} 202 _n respectively count the pulses P 1 to Pn, calculate the frequencies H 1 to Hn of each luminance level for each frame, and output the calculated H 1 to Hn to the cumulative frequency distribution creation circuit 203. The cumulative frequency distribution creating circuit 203, which is a frequency distribution detecting means for detecting the frequency distribution of each value of the luminance signal Y, accumulates the frequencies H1 to Hn of each luminance level of the luminance signal Y for each frame, thereby accumulating the cumulative frequency. A distribution RD is generated, and the cumulative frequency distribution RD is output to the gain control circuit 204.

  A predetermined correction gain limiting parameter GP is input to the gain control circuit 204. In the first embodiment of the present invention, the value of the correction gain restriction parameter GP is set in advance. Then, the gain control circuit 204 performs processing for gain correction on the cumulative frequency distribution RD based on the correction gain restriction parameter GP to obtain a corrected cumulative frequency distribution GR, and outputs the corrected cumulative frequency distribution GR to the normalization circuit 205. . The processing of the gain control circuit 204 will be described later.

  The normalization circuit 205 normalizes the given corrected cumulative frequency distribution GR to obtain a normalized cumulative frequency distribution HST, and outputs the normalized cumulative frequency distribution HST.

  Next, regarding the details of the operations of the gradation information calculation circuit 101 in FIG. 1 and the luminance distribution extraction circuit 102 in FIG. 2, along the processing from the calculation of the luminance signal Y to the calculation of the normalized cumulative frequency distribution HST, This will be described using an example.

  FIG. 3 is a diagram illustrating an example of a frequency distribution of primary color signals. 3A is a diagram illustrating an example of the frequency distribution of the red primary color signal RI, FIG. 3B is a diagram illustrating an example of the frequency distribution of the green primary color signal GI, and FIG. 3C is a blue primary color. It is a figure which shows frequency distribution of signal BI. 3A, 3B, and 3C, the horizontal axis represents the red input luminance level (the value of the red primary color signal RI), the green input luminance level (the value of the green primary color signal GI), and the blue input luminance level (blue). The value of the primary color signal BI), and the vertical axis represents the frequency.

The gradation information calculation circuit 101 in FIG. 1 calculates the luminance signal Y from the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI according to the following equation.
Y = α ・ RI + β ・ GI + γ ・ BI
In the above equation, α, β, and γ are predetermined coefficients. As described above, the gradation information calculation circuit 101 calculates the luminance signal Y by multiplying the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI by respective predetermined coefficients and adding them. Then, the luminance distribution extraction circuit 102 calculates a normalized cumulative frequency distribution HST from the luminance signal Y.

  FIG. 4 is a diagram showing an example of the frequency distribution of the luminance signal Y calculated by the gradation information calculation circuit 101 of the gradation correction apparatus according to the first embodiment of the present invention. The horizontal axis in FIG. 4 indicates the luminance level (value of the luminance signal Y), and the vertical axis indicates the frequency. In the first embodiment of the present invention, the luminance level has a value from 0 to 255.

  In the example illustrated in FIG. 4, the frequency is 0 in the low range a and the high range b. Therefore, the ranges a and b have a margin that can widen the frequency distribution by the smoothing process. In order to perform the smoothing process, first, the frequency of each luminance level is cumulatively calculated in order to calculate the cumulative frequency distribution RD. The calculation of the cumulative frequency distribution RD is performed by the cumulative frequency distribution creation circuit 203 in the luminance distribution extraction circuit 102 as described above.

  FIG. 5 is a diagram showing an example of the cumulative frequency distribution RD created by the cumulative frequency distribution creation circuit 203 of the gradation correction apparatus according to the first embodiment of the present invention. The horizontal axis in FIG. 5 represents the luminance level (value of the luminance signal Y), and the vertical axis represents the cumulative frequency. As described above, the cumulative frequency distribution creation circuit 203 calculates the cumulative frequency distribution RD in which the respective frequencies at the respective luminance levels from the minimum luminance level to the maximum luminance level are accumulated.

  Further, the cumulative frequency distribution creation circuit 203 may be configured to detect a feature amount such as an average value, a mode value, a minimum value, a maximum value, a deviation coefficient, a white area, and a black area of the luminance level. Based on the detected feature values, the normalization circuit 205 calculates a normalized maximum luminance level used for normalization of the corrected cumulative frequency distribution GR.

  Next, the gain control circuit 204 generates an offset based on the correction gain limiting parameter GP. Here, this offset will be described.

  FIG. 6 is a diagram illustrating an example of an offset generated by the gain control circuit 204 of the gradation correction apparatus according to the first embodiment of the present invention. The horizontal axis in FIG. 6 indicates the luminance level, and the vertical axis indicates the offset value. The gain control circuit 204 gradually increases from the minimum luminance level as shown in FIG. 6 to the maximum luminance level, and generates a different offset for each luminance level. Then, a corrected cumulative frequency distribution GR is generated by adding an offset corresponding to each luminance level to the cumulative frequency distribution RD shown in FIG.

  At this time, the gain control circuit 204 can change the offset based on the correction gain limiting parameter GP. For example, when the value of the correction gain limiting parameter GP is small, the slope of the offset OF is increased as shown by a solid line, and when the value of the correction gain limiting parameter GP is large, the slope of the offset OF is shown as shown by a broken line. Can be reduced.

  FIG. 7 is a diagram illustrating an example of the corrected cumulative frequency distribution GR generated by the gain control circuit 204 of the gradation correction apparatus. The horizontal axis in FIG. 7 indicates the luminance level, and the vertical axis indicates the cumulative frequency. Further, the corrected cumulative frequency distribution GR when the offset OF has a large slope is indicated by a solid line, and the corrected cumulative frequency distribution GR when the offset OF has a small slope is indicated by a broken line. As shown in FIG. 6, the maximum value of the corrected cumulative frequency distribution GR increases as the slope of the offset OF increases.

  The normalization circuit 205 normalizes the corrected cumulative frequency distribution GR output from the gain control circuit 204 to create a normalized cumulative frequency distribution HST. At that time, the normalization circuit 205 performs a normalization operation of the corrected cumulative frequency distribution GR so that the maximum cumulative frequency of the normalized cumulative frequency distribution HST becomes the maximum luminance level obtained by the cumulative frequency distribution creation circuit 203.

  FIG. 8 is a diagram illustrating an example of the normalized cumulative frequency distribution HST generated by the normalization circuit 205 of the gradation correction apparatus. The horizontal axis in FIG. 8 indicates the luminance level, and the vertical axis indicates the normalized frequency. Also, the normalized cumulative frequency distribution HST when the offset OF shown in FIG. 6 is large is indicated by a solid line, and the normalized cumulative frequency distribution HST when the offset OF is small is indicated by a broken line. When the horizontal axis is the X axis and the vertical axis is the Y axis, the ramp straight line LP indicated by a linear function of Y = X is indicated by a one-dot chain line.

  As shown in FIG. 8, when the slope of the offset OF is large, that is, when the value of the correction gain restriction parameter GP is small, the displacement amount of the normalized cumulative frequency distribution HST with respect to the ramp straight line LP is small. This is because the cumulative frequency increases as the offset increases, and as a result, the parameter for normalization increases and the normalized cumulative frequency distribution HST is averaged. Accordingly, when the slope of the offset OF is small, that is, when the value of the correction gain restriction parameter GP is large, the displacement amount of the normalized cumulative frequency distribution HST with respect to the ramp straight line LP becomes large. The above is the description from the calculation of the luminance signal Y to the calculation of the normalized cumulative frequency distribution HST. Next, details of the operation from the calculated normalized cumulative frequency distribution HST to the output of the output signals RO, GO, and BO will be described.

  The gradation correction conversion table creation circuit 104 shown in FIG. 1 calculates the correction amount ΔY by subtracting the ramp straight line LP from the normalized cumulative frequency distribution HST obtained by the normalization circuit 205. FIG. 9 is a diagram showing an example of the distribution of the correction amount ΔY calculated by the gradation correction conversion table creation circuit 104 of the gradation correction apparatus according to the first embodiment of the present invention. In FIG. 9, the horizontal axis indicates the luminance level, and the vertical axis indicates the correction amount ΔY. The correction amount ΔY when the offset OF has a large inclination is indicated by a solid line, and the correction amount ΔY when the offset OF has a small inclination is indicated by a broken line. When the offset OF has a large inclination, that is, when the value of the correction gain restriction parameter GP is small, the correction amount ΔY is small, and when the offset OF has a small inclination, that is, when the value of the correction gain restriction parameter GP is large, the correction amount ΔY. As described with reference to FIG. Therefore, the correction gain for smoothing can be set by the value of the correction gain restriction parameter GP.

  In the first embodiment of the present invention, the gradation correction conversion table creation circuit 104 in the correction information generation unit 150 includes a lookup table (LUT) memory (not shown) as the correction information storage unit. Have. Then, the luminance signal Y is made to correspond to the address of the LUT memory, and the correction amount ΔY is stored as data at that address. That is, the correction amount ΔY stored in the LUT memory becomes a gradation correction conversion table. The gradation correction conversion table creation circuit 104 reads the correction amount ΔY, which is correction information, from the corresponding address of the LUT memory, using the luminance signal Y input via the signal selection circuit 103 during the vertical effective scanning period as an address signal, It outputs to the correction change rate calculation circuit 105.

  The correction change rate calculation circuit 105 divides ΔY input from the gradation correction conversion table creation circuit 104 by the luminance signal Y input from the gradation information calculation circuit 101. In this way, the corrected change rate YK is calculated and output to the signal selection circuits 107, 108, and 109 as a control signal of the signal selection circuit, and is output to the multiplication circuits 110, 111, and 112 as an operation signal of the multiplication circuit.

  FIG. 10 is a diagram showing an example of the distribution of the correction change amount YK calculated by the correction change rate calculation circuit 105 of the gradation correction apparatus according to the first embodiment of the present invention. The horizontal axis in FIG. 10 indicates the luminance level, and the vertical axis indicates the correction change amount YK. However, when the luminance level Y = 0, the correction change amount YK = 0. Further, the correction change amount YK when the offset OF has a large inclination is indicated by a solid line, and the correction change amount YK when the offset OF has a small inclination is indicated by a broken line.

  The correction for the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI is switched as described above according to the value of the correction change amount YK. The detailed operation will be described.

When the value of the correction change amount YK is 0 or more, that is, when YK shown in FIG. 10 is in the positive region, as shown in FIG. 1, the signal selection circuits 107, 108, 109 to the multiplication circuit 110 are used. , 111, 112 are inputted with SR = RI, SG = GI, and SB = BI as the red selection signal SR, the green selection signal SG, and the blue selection signal SB, respectively. The multiplication circuits 110, 111, and 112 calculate the red multiplication signal MR, the green multiplication signal MG, and the blue multiplication signal MB based on the equations (1), (2), and (3), respectively, and the addition circuits 113, 114 , 115. Here, assuming that the luminance signal after smoothing processing for the luminance signal Y is Y ′, Equations (1), (2), and (3) are as follows.
MR = YK · SR = (ΔY / Y) · RI = {(Y′−Y) / Y} · RI (1)
MG = YK · SG = (ΔY / Y) · GI = {(Y′−Y) / Y} · GI (2)
MB = YK · SB = (ΔY / Y) · BI = {(Y′−Y) / Y} · BI (3)
The adder circuits 113, 114, and 115 calculate the red primary color signal RO, the green primary color signal GO, and the blue primary color signal BO based on the following formulas (4), (5), and (6).
RO = RI + MR = RI + {(Y′−Y) / Y} · RI = (Y ′ / Y) · RI (4)
GO = GI + MG = GI + {(Y′−Y) / Y} · GI = (Y ′ / Y) · GI (5)
BO = BI + MB = BI + {(Y′−Y) / Y} · BI = (Y ′ / Y) · BI (6)
However, as described above, the application of Expressions (1) to (6) is applied when the value of the correction change amount YK is 0 or more, and is limited to ΔY ≧ 0, that is, Y ′ ≧ Y.

  On the other hand, when the value of the correction change amount YK is smaller than 0 (when YK is in a negative region in FIG. 10), that is, when ΔY <0, the signal selection circuits 107, 108, 109 to the multiplication circuit 110, The red selection signal SR, the green selection signal SG, and the blue selection signal SB output to 111 and 112 are SR = BLR, SG = BLG, and SB = BLB, respectively.

Here, the red mixed signal BLR calculated from the mixed signal calculating circuit 106 is a mixed signal of the red primary color signal RI and the luminance signal Y, the green mixed signal BLG is a mixed signal of the green primary color signal GI and the luminance signal Y, The blue mixed signal BLB is a mixed signal of the blue primary color signal BI and the luminance signal Y, and is calculated based on the equations (7), (8), and (9), respectively. If the mixing ratio of the primary color signal is a (a = 0 to 1) and the mixing ratio of the luminance signal is b (b = 0 to 1), Expressions (7), (8), and (9) are It is expressed as follows.
BLR = a · RI + b · Y (where a + b = 1) (7)
BLG = a · GI + b · Y (where a + b = 1) (8)
BLB = a · BI + b · Y (where a + b = 1) (9)
Further, the multiplication circuits 110, 111, and 112 calculate the red multiplication signal MR, the green multiplication signal MG, and the blue multiplication signal MB based on the following expressions (10), (11), and (12), and add them. Output to circuits 113, 114, and 115.
MR = YK · SR = (ΔY / Y) · BLR = {(Y′−Y) / Y} · BLR (10)
MG = YK · SG = (ΔY / Y) · BLG = {(Y′−Y) / Y} · BLG (11)
MB = YK · SB = (ΔY / Y) · BLB = {(Y′−Y) / Y} · BLB (12)
The adder circuits 113, 114, and 115 calculate the red primary color signal RO, the green primary color signal GO, and the blue primary color signal BO based on the following formulas (13), (14), and (15), and output them. To do.
RO = RI + MR = RI + {(Y′−Y) / Y} · BLR (13)
GO = GI + MG = GI + {(Y′−Y) / Y} · BLG (14)
BO = BI + MB = BI + {(Y′−Y) / Y} · BLB (15)
However, as described above, the expressions (7) to (15) are applied when the value of the correction change amount YK is smaller than 0 and limited to when ΔY <0.

  The above is the description of the operation from the normalized cumulative frequency distribution HST to the output of the output signals RO, GO, and BO. Here, the output signals RO, GO, and BO will be described in more detail.

  First, when ΔY is a value greater than or equal to 0, that is, when the smoothed luminance signal Y ′ is larger than the luminance signal Y, the calculation is performed based on the equations (4), (5), and (6). The three digital primary color signals RO, GO and BO will be described. FIG. 11 is a diagram showing an example of the relationship between the luminance signal Y and the smoothed luminance signal Y ′ in the first embodiment of the present invention. The horizontal axis in FIG. 11 indicates the value of the luminance signal Y, and the vertical axis indicates the value of the luminance signal Y ′ after the smoothing process.

  In the example of FIG. 11, when the value of the luminance signal Y is high, the luminance signal Y ′ after the smoothing process has a higher value than the value of the luminance signal Y. That is, when the value of the luminance signal Y is relatively high, the luminance signal Y ′ after the smoothing process is smoothed to a range having a higher luminance level than the luminance signal Y.

  FIG. 12 is a diagram illustrating an example of a relationship between luminance levels of three primary color signals before and after the smoothing process when ΔY ≧ 0 in the first embodiment of the present invention. FIG. 12A is a diagram showing the relationship between the luminance levels of the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI before smoothing processing of one pixel, and FIG. It is a figure which shows the relationship of the luminance level of the red primary color signal RO after the smoothing process of a pixel, the green primary color signal GO, and the blue primary color signal BO.

  In the example shown in FIG. 12A, among the three digital signals, the luminance level of the red primary color signal RI is the highest, the luminance level of the blue primary color signal BI is next highest, and the luminance level of the green primary color signal GI is the highest. It is getting smaller. Then, the red primary color signal RO, the green primary color signal GI, and the blue primary color signal BI are multiplied by the same coefficient Y ′ / Y to calculate the red primary color signal RO, the green primary color signal GO, and the blue primary color signal BO. To do. Therefore, as shown in FIG. 12B, the correction amount for the red primary color signal RI having the highest luminance level among the three digital signals is the largest, and then the correction amount for the blue primary color signal BI is increased. The correction amount for the green primary color signal GI is the smallest.

  At this time, Y ′ / Y, which is a common coefficient, is multiplied to each of the three primary color signals, so that the ratio of the input red primary color signal RI, green primary color signal GI, and blue primary color signal BI is obtained by correction. The ratio of the red primary color signal RO, the green primary color signal GO, and the blue primary color signal BO is substantially equal, and the color balance hardly changes.

  Next, when ΔY is a value smaller than 0, that is, when the luminance signal Y ′ after the smoothing process is smaller than the luminance signal Y, based on the equations (13), (14), and (15). The three calculated digital primary color signals RO, GO, and BO will be described. In order to make the description easy to understand, the description will be made assuming that the mixing ratio a of primary color signals is zero.

When a = 0, the red primary color signal RO, the green primary color signal GO, and the blue primary color signal BO are respectively RO = RI + Y′−Y based on the equations (13), (14), and (15).
GO = GI + Y′−Y
BO = BI + Y′−Y
It becomes. Therefore, the red primary color signal RO, the green primary color signal GO, and the blue primary color signal BO are calculated by uniformly subtracting YY ′ from the input primary color signals RI, GI, and BI.

  FIG. 13 is a diagram illustrating an example of the relationship between the luminance levels of the three primary color signals before and after the smoothing process when ΔY <0 in the first embodiment of the present invention. FIG. 13A is a diagram showing the relationship between the luminance levels of the red primary color signal RI, green primary color signal GI, and blue primary color signal BI before smoothing processing of a certain pixel. FIG. It is a figure which shows the relationship of the luminance level of the red primary color signal RO after the smoothing process of a pixel, the green primary color signal GO, and the blue primary color signal BO.

  In the example shown in FIG. 13A, as in the example shown in FIG. 12, the luminance level of the red primary color signal RI is the highest among the three digital signals, and the luminance level of the blue primary color signal BI is the next highest. The luminance level of the green primary color signal GI is the smallest. Then, Y-Y ′ is uniformly subtracted from the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI to calculate the red primary color signal RO, the green primary color signal GO, and the blue primary color signal BO. Therefore, as shown in FIG. 13B, the respective difference values of the input red primary color signal RI, green primary color signal GI, and blue primary color signal BI, and the red primary color signal RO and green primary color signal obtained by the correction. The difference values of GO and blue primary color signal BO are substantially equal.

  In general, in the HSV color space, the saturation is a value obtained by dividing the difference value between the signal having the maximum luminance level and the signal having the minimum luminance level among the three digital signals by the signal having the maximum luminance level. . In the first embodiment of the present invention, as described above, the correction is performed while the respective difference values of the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI are stored. By doing so, it is possible to suppress a decrease in saturation, that is, loss of vividness of appearance such as color loss.

  When the primary color signal mixing ratio a = 0, the saturation change rate due to the correction is maximized, and as the primary color signal mixing ratio a is greater than 0, the saturation change rate due to the correction decreases, and the primary color signal When the mixing ratio a = 1, there is no change in saturation due to the correction.

  The three digital primary color signals calculated by the above processing will be described. FIG. 14 is a diagram showing the frequency distribution of the output signal when the input signal shown in FIG. 3 is corrected by the gradation correction apparatus according to the first embodiment of the present invention. 14A shows the frequency distribution of the red primary color signal RO, FIG. 14B shows the frequency distribution of the green primary color signal GO, and FIG. 14C shows the frequency of the blue primary color signal BO. It is a figure which shows distribution. 14A, 14B, and 14C, the horizontal axis indicates the output luminance level of each primary color signal, and the vertical axis indicates the frequency.

  As shown in FIG. 14A, the frequency distribution of the red primary color signal RO is wider than the frequency distribution of the red primary color signal RI shown in FIG. 3A from a low luminance level to a high luminance level. The range has been expanded. Further, as shown in FIG. 14B, the frequency distribution of the green primary color signal GO is also lower from the low luminance level to the high luminance level than the frequency distribution of the green primary color signal GI shown in FIG. It has been expanded to a wider range. Further, as shown in FIG. 14 (c), the frequency distribution of the blue primary color signal BO is lower than the frequency distribution of the blue primary color signal BI shown in FIG. 3 (c) from a low luminance level to a high luminance level. It has been expanded to a wider range. Therefore, in the first embodiment of the present invention, the luminance signal Y is calculated from the three input primary color signals, is smoothed, and the primary color signal is corrected so that the high-contrast primary color signal is obtained. Can be output. Further, by dividing the region where the luminance level is increased by the smoothing of the luminance signal Y and the region where the luminance level is decreased, and by applying different corrections to the primary color signal in each region, the change in the color balance in the region where the luminance level increases In contrast, in a region where the luminance level is lowered, high contrast can be realized while suppressing a decrease in saturation.

  In the first embodiment of the present invention, the configuration in which the gradation information calculation circuit 101 calculates the luminance signal Y as luminance correlation information from the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI has been described. However, the present invention is not limited to this. For example, another signal having a correlation with the luminance may be calculated from the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI to obtain the luminance correlation information.

  Further, although the red mixed signal BLR, the green mixed signal BLG, and the blue mixed signal BLB calculated by the mixed signal calculation circuit 106 have been described as mixed signals including the luminance signal Y, the present invention is not limited to this. For example, it may be a mixed signal including other signals having a correlation with all the signals of the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI.

  In the gradation correction apparatus according to the present invention, the luminance level is increased by dividing the region where the luminance level is increased by the smoothing of the luminance signal Y and the region where the luminance level is decreased, and applying different corrections to the primary color signal in each region. It is useful as a tone correction device that corrects the tone of the video signal because it can achieve high contrast while suppressing the change in color balance in the region and suppressing the decrease in saturation in the region where the luminance level decreases. is there.

The block diagram which shows the structure of the gradation correction apparatus in the 1st Embodiment of this invention. The block diagram which shows the structure of the luminance distribution extraction circuit of the same gradation correction apparatus The figure which shows an example of the frequency distribution of a primary color signal The figure which shows an example of the frequency distribution of the luminance signal Y calculated in the gradation information calculation circuit of the gradation correction apparatus in the 1st Embodiment of this invention. The figure which shows an example of the cumulative frequency distribution RD produced by the cumulative frequency distribution creation circuit of the gradation correction apparatus The figure which shows an example of the offset produced | generated by the gain control circuit of the same gradation correction apparatus The figure which shows an example of the correction | amendment cumulative frequency distribution GR produced | generated by the gain control circuit of the same gradation correction apparatus The figure which shows an example of the normalization accumulation frequency distribution HST produced | generated by the normalization circuit of the same gradation correction apparatus The figure which shows an example of distribution of correction amount (DELTA) Y calculated by the gradation correction conversion table preparation circuit of the gradation correction apparatus The figure which shows an example of distribution of the correction variation | change_quantity YK calculated by the correction change rate calculation circuit of the same gradation correction apparatus. The figure which shows an example of the relationship between the luminance signal Y in the 1st Embodiment of this invention, and the luminance signal Y 'after a smoothing process. The figure which shows an example of the relationship of the luminance level of three primary color signals before the smoothing process in case of (DELTA) Y> = 0 in the 1st Embodiment of this invention, and a smoothing process. The figure which shows an example of the relationship of the luminance level of three primary color signals before the smoothing process in case of (DELTA) Y <0 in the 1st Embodiment of this invention, and a smoothing process. The figure which shows the frequency distribution of the output signal at the time of correcting the input signal shown in FIG. 3 with the same gradation correction apparatus Comparison of brightness distribution before and after smoothing by conventional technology

Explanation of symbols

101 gradation information calculation circuit 102 luminance distribution extraction circuit 103, 107, 108, 109 signal selection circuit 104 gradation correction conversion table creation circuit 105 correction change rate calculation circuit 106 mixed signal calculation circuit 110, 111, 112 multiplication circuits 113, 114 , 115 Adder circuit 150 Correction information generation means 201 Address decoder 202 _{1 to} 202 _n counter 203 Cumulative frequency distribution creation circuit 204 Gain control circuit 205 Normalization circuit

Claims (4)

Luminance correlation information generating means for generating luminance correlation information having correlation with luminance from a plurality of input primary color signals;
Correction information generating means for generating correction information for smoothing the luminance distribution extracted based on the luminance correlation information;
Correction change rate calculating means for calculating a correction change rate based on the luminance correlation information and the correction information;
A mixed signal generating means for generating a mixed signal having a correlation with all of the plurality of input primary color signals,
A gradation correction apparatus configured to perform correction on the plurality of input primary color signals depending on whether the value of the correction change rate is a value of 0 or more or a value smaller than 0. When the value of the correction change rate is smaller than 0, the correction change rate value is multiplied by the mixed signal of the mixed signal generating means to generate a multiplication signal, and the multiplication signal and a plurality of primary color signals inputted thereto The gradation correction apparatus according to claim 1, wherein an addition signal obtained by adding and is output. When the value of the correction change rate is a value equal to or greater than 0, a multiplication signal is generated by multiplying the value of the correction change rate and the input primary color signals, and the multiplication signal and the input plurality of input signals are generated. 2. The gradation correction apparatus according to claim 1, wherein an addition signal obtained by adding the primary color signal is output. The correction information generation means detects frequency distribution of the appearance frequency of each value of the brightness correlation information for each frame, and stores the correction amount at each value as correction information based on the distribution of the appearance frequency. 2. The apparatus according to claim 1, further comprising: an information storage unit configured to calculate a correction change rate corresponding to the luminance correlation information based on the correction information read from the correction information storage unit. Gradation correction device.

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