JP4397623B2 - Tone correction device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gradation correction apparatus and a gradation correction method for correcting gradation of a video signal.
[0002]
[Prior art]
In a display device that performs gradation display in a digital manner, such as a plasma display panel (hereinafter referred to as PDP) or a liquid crystal display device (hereinafter referred to as LCD), a limited gradation dynamic range is effectively utilized. In order to achieve high contrast, smoothing processing of the luminance distribution of the video signal is performed (see, for example, Patent Documents 1 to 4). In such a luminance distribution smoothing process, the contrast is improved in order to make the image appear clearer, and the overall dark image is improved more brightly.
[0003]
FIG. 13A is a diagram showing an example of a luminance frequency distribution in one frame before the smoothing process, and FIG. 13B is a luminance frequency in one frame after the smoothing process by the conventional gradation correction apparatus. It is a figure which shows distribution. 13A and 13B, the horizontal axis indicates the luminance level, and the vertical axis indicates the appearance frequency (hereinafter abbreviated as frequency).
[0004]
In the example of FIG. 13A, the frequency is high at an intermediate luminance level. According to the smoothing process, the frequency distribution is smoothed over the entire range of luminance levels as shown in FIG. Thereby, high contrast is realized.
[0005]
In general, the luminance distribution smoothing process is performed on the luminance signal. Therefore, in the conventional gradation correction device, the red primary color signal (R signal), the green primary color signal (G signal), and the blue primary color signal (B signal) are converted into a luminance signal and two color difference signals by color coordinate conversion. A luminance distribution smoothing process is performed on the signal. Thereafter, the processed luminance signal and the two color difference signals are converted into a red primary color signal, a green primary color signal, and a blue primary color signal by inverse color coordinate conversion (see, for example, Patent Documents 5 and 6).
[0006]
[Patent Document 1]
Japanese Unexamined Patent Publication No. 63-040472
[Patent Document 2]
JP 08-115417 A
[Patent Document 3]
JP 2002-165095 A
[Patent Document 4]
Japanese Patent Laid-Open No. 08-023460
[Patent Document 5]
Japanese Patent Laid-Open No. 09-247483
[Patent Document 6]
JP 2003-009172 A
[0007]
[Problems to be solved by the invention]
In the conventional gradation correction device, an arithmetic error occurs when the three primary color signals are converted into a luminance signal and two color difference signals by color coordinate conversion, and the smoothed luminance signal and the two color difference signals are converted into colors. A calculation error also occurs when the three primary color signals are converted by the inverse coordinate transformation. As a result, the three primary color signals obtained by the smoothing process are degraded, and the displayed video is degraded.
[0008]
In addition, nine multiplications are necessary in the color coordinate conversion, and nine multiplications are also necessary in the color coordinate reverse conversion. Therefore, when the color coordinate conversion circuit for performing color coordinate conversion and the color coordinate reverse conversion circuit for performing color coordinate reverse conversion are realized by hardware, a total of 18 multiplication circuits are required. Therefore, the circuit scale of the gradation correction device increases.
[0009]
An object of the present invention is to provide a gradation correction apparatus and a gradation correction method capable of increasing the contrast of a primary color signal without increasing the circuit scale and without causing image deterioration.
[0010]
[Means for Solving the Problems]
The gradation correction apparatus according to 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 a luminance correlation generated by the luminance correlation information generating unit. Correction information generating means for generating correction information for smoothing the luminance distribution based on the information, and luminance correlation information generated by the luminance correlation information generating means based on the correction information generated by the correction information generating means. A correction ratio calculation unit that calculates a corresponding correction ratio and a multiplication unit that multiplies each of the input primary color signals by the correction ratio calculated by the correction ratio calculation unit.
[0011]
In the gradation correction apparatus according to the present invention, luminance correlation information having a correlation with luminance is generated from a plurality of input primary color signals by the luminance correlation information generating means, and the luminance distribution information is generated based on the luminance correlation information. Correction information for the smoothing process is generated by the correction information generation means. Then, based on the correction information generated by the correction information generating means, a correction ratio corresponding to the luminance correlation information generated by the luminance correlation information generating means is calculated by the correction ratio calculating means, and a plurality of the correction ratios inputted thereto are inputted. The primary color signals are respectively multiplied by multiplication means.
[0012]
As described above, since the luminance distribution is smoothed based on correction information common to a plurality of primary color signals, the circuit scale can be reduced. In addition, since the luminance distribution is smoothed on each of the plurality of input primary color signals, the calculation error is small and the deterioration of the video is prevented. Therefore, it is possible to increase the contrast of the primary color signal without increasing the circuit scale and without causing deterioration of the image.
[0013]
Furthermore, since a plurality of primary color signals are multiplied by a common correction ratio, a change in color balance is unlikely to occur between the input primary color signals and the obtained primary color signals.
[0014]
The correction ratio calculation unit may calculate a ratio between the correction information generated by the correction information generation unit and the luminance correlation information generated by the luminance correlation information generation unit and the luminance correlation information as a correction ratio. In this case, the correction ratio can be easily calculated with a simple circuit configuration.
[0015]
The luminance correlation information generation unit may generate a luminance signal as the luminance correlation information.
In this case, since the luminance signal includes an average element of the luminances of the plurality of primary color signals, it is possible to smooth the average luminance distribution of the plurality of primary color signals. As a result, high contrast can be achieved without degrading the image quality of the video.
[0016]
A plurality of primary color signals including a red primary color signal, a green primary color signal, and a blue primary color signal; and a multiplying unit that multiplies the input red primary color signal by the correction ratio calculated by the correction ratio calculating unit; A second multiplication circuit that multiplies the input green primary color signal by the correction ratio calculated by the correction ratio calculation means; and a third multiplier that multiplies the input blue primary color signal by the correction ratio calculated by the correction ratio calculation means. The multiplication circuit may be included.
[0017]
In the multiplication means, the correction ratio calculated by the correction ratio calculation means is multiplied by the red primary color signal input by the first multiplication circuit, and the correction ratio calculated by the correction ratio calculation means is input by the second multiplication circuit. The blue primary color signal input by the third multiplication circuit is multiplied by the corrected green primary color signal and the correction ratio calculated by the correction ratio calculating means.
[0018]
In this case, an image can be displayed as it is using the red primary color signal, the green primary color signal, and the blue primary color signal without performing color coordinate conversion and color coordinate reverse conversion. Thereby, the circuit scale can be reduced and the deterioration of the video is prevented.
[0019]
The correction information generating means is based on the frequency distribution detecting means for detecting the distribution of the appearance frequency of each value of the luminance correlation information generated by the luminance correlation information generating means for each frame, and the distribution detected by the frequency distribution detecting means. Correction information storage means for storing the correction amount at each value as correction information, the correction ratio calculation means is a luminance correlation generated by the luminance correlation information generation means based on the correction information read from the correction information storage means A correction ratio corresponding to the information may be calculated.
[0020]
In this case, the distribution of the frequency of appearance of each value of the luminance correlation information is detected for each frame, and the correction amount for each value is stored as correction information in the correction information storage means within a predetermined range based on the distribution. Then, a correction ratio corresponding to the luminance correlation information is calculated based on the correction information read from the correction information storage unit.
[0021]
According to a second aspect of the present invention, there is provided a gradation correction method comprising: generating luminance correlation information having a correlation with luminance from a plurality of input primary color signals; and smoothing a luminance distribution based on the generated luminance correlation information. Generating correction information for the conversion processing, calculating a correction ratio corresponding to the luminance correlation information generated based on the generated correction information, and a plurality of primary colors inputted with the calculated correction ratio Each step of multiplying the signals.
[0022]
In the gradation correction method according to the second invention, luminance correlation information having a correlation with the luminance is generated from the plurality of input primary color signals, and the luminance distribution smoothing process is performed based on the luminance correlation information. Correction information is generated. Then, a correction ratio corresponding to the luminance correlation information generated based on the generated correction information is calculated, and the input primary color signals are respectively multiplied by the correction ratio.
[0023]
As described above, since the luminance distribution is smoothed based on correction information common to a plurality of primary color signals, the circuit scale can be reduced. In addition, since the luminance distribution is smoothed on each of the plurality of input primary color signals, the calculation error is small and the deterioration of the video is prevented. Therefore, it is possible to increase the contrast of the primary color signal without increasing the circuit scale and without causing deterioration of the image.
[0024]
Furthermore, since a plurality of primary color signals are multiplied by a common correction ratio, a change in color balance is unlikely to occur between the input primary color signals and the obtained primary color signals.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a gradation correction apparatus according to an embodiment of the present invention will be described.
[0026]
FIG. 1 is a block diagram showing a configuration of a gradation correction apparatus according to an embodiment of the present invention.
[0027]
The gradation correction apparatus 100 of FIG. 1 includes a gradation information calculation circuit 5, a conversion ratio calculation circuit 7, a luminance distribution extraction circuit 10, a switching circuit 11, a gradation correction conversion table creation circuit 12, and multiplication circuits 21, 22, and 23. Including.
[0028]
A red primary color signal (R signal) RI, a green primary color signal (G signal) GI, and a blue primary color signal (B signal) BI are input to the gradation information calculation circuit 5 of the gradation correction apparatus 100 of FIG. Further, the red primary color signal RI is input to the multiplication circuit 21, the green primary color signal GI is input to the multiplication circuit 22, and the blue primary color signal BI is input to the multiplication circuit 23.
[0029]
Here, the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI are digital primary color signals, respectively. The value of the red primary color signal RI, the value of the green primary color signal GI, and the value of the blue primary color signal BI are respectively a red luminance level (gradation), a green luminance level (gradation), and a blue luminance level (gradation). To express.
[0030]
The gradation information calculation circuit 5 includes three multiplication circuits, and calculates the luminance signal Y1 from the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI. The gradation information calculation circuit 5 supplies the calculated luminance signal Y1 to the conversion ratio calculation circuit 7, the luminance distribution extraction circuit 10, and the switching circuit 11.
[0031]
The luminance distribution extraction circuit 10 performs a luminance distribution extraction process, which will be described later, from the luminance signal Y1, creates a normalized cumulative frequency distribution SS, and gives it to the switching circuit 11.
[0032]
The switching circuit 11 provides the luminance signal Y1 to the gradation correction conversion table creation circuit 12 during the vertical effective scanning period, and provides the normalized cumulative frequency distribution SS to the gradation correction conversion table creation circuit 12 during the vertical blanking period. Here, the vertical effective scanning period refers to a period during which an image is displayed in one vertical scanning period, and the vertical blanking period refers to the vertical scanning start point from the vertical scanning end point in one vertical blanking period. The period to return to.
[0033]
The gradation correction conversion table creation circuit 12 creates and stores a gradation correction conversion table for smoothing processing based on the normalized cumulative frequency distribution SS in the vertical blanking period. In addition, the gradation correction conversion table creation circuit 12 generates a correction amount ΔY from the luminance signal Y1 using the gradation correction conversion table in the vertical effective scanning period, and supplies the correction amount ΔY to the conversion ratio calculation circuit 7.
[0034]
The conversion ratio calculation circuit 7 includes one multiplication circuit, and uses the correction amount ΔY and the given luminance signal Y1 to convert the luminance distribution smoothing process for the three digital primary color signals. Is calculated. A method for calculating the conversion ratio YR will be described later. The conversion ratio calculation circuit 7 gives the calculated conversion ratio YR to the multiplication circuits 21, 22 and 23.
[0035]
The multiplication circuit 21 multiplies the red primary color signal RI and the conversion ratio YR, and outputs the multiplication result as a red primary color signal R0. The multiplication circuit 22 multiplies the green primary color signal GI and the conversion ratio YR, and outputs the multiplication result as the green primary color signal G0. The multiplication circuit 23 multiplies the blue primary color signal BI and the conversion ratio YR, and outputs the multiplication result as the blue primary color signal B0.
[0036]
Next, the configuration and operation of the luminance distribution extraction circuit 10 will be described. FIG. 2 is a block diagram showing a configuration of the luminance distribution extraction circuit 10 of FIG.
[0037]
The luminance distribution extraction circuit 10 shown in FIG. 2 includes an address decoder 30 and n counters 4. ₁ , 4 ₂ , ..., 4 _n (Hereinafter 4 ₁ ~ 4 _n A cumulative frequency distribution generation circuit 50, a gain control circuit 60, and a normalization circuit 70. Here, n corresponds to the number of luminance levels (the number of gradations). For example, n is 256 when the luminance signal Y1 has 8 bits. Hereinafter, for ease of understanding, n = 256, but the number of gradations is not limited to this, and can be set to any value.
[0038]
First, the luminance signal Y1 is given to the address decoder 30. The address decoder 30 counters the counter 4 according to the value of the luminance signal Y1. ₁ ~ 4 _n Pulse P to either ₁ ~ P _n give.
[0039]
For example, when the value of the luminance signal Y1 is “0”, the address decoder 30 ₁ Pulse P ₁ When the value of the luminance signal Y1 is “1”, the counter 4 ₂ Pulse P ₂ When the value of the luminance signal Y1 is n-1, the counter 4 _n Pulse P _n give.
[0040]
Counter 4 ₁ ~ 4 _n Are each pulse P ₁ ~ P _n And the frequency of appearance of each luminance level for each frame (hereinafter abbreviated as frequency) H ₁ ~ H _n Is given to the cumulative frequency distribution creation circuit 50. The cumulative frequency distribution creation circuit 50 is configured to calculate the frequency H of each luminance level for each frame. ₁ ~ H _n Is accumulated to generate a cumulative frequency distribution RD, and the cumulative frequency distribution RD is given to the gain control circuit 60.
[0041]
The gain control circuit 60 is given a predetermined correction gain limiting parameter GP. In the present embodiment, the value of the correction gain restriction parameter GP is set in advance. The gain control circuit 60 performs a process for gain correction on the cumulative frequency distribution RD given from the cumulative frequency distribution creation circuit 50 based on the correction gain restriction parameter GP, and gives the corrected cumulative frequency distribution GR to the normalization circuit 70. . The processing of the gain control circuit 60 will be described later.
[0042]
The normalization circuit 70 performs normalization processing on the given corrected cumulative frequency distribution GR and outputs a normalized cumulative frequency distribution SS.
[0043]
Here, details of the operations of the gradation information calculation circuit 5 in FIG. 1 and the luminance distribution extraction circuit 10 in FIG. 2 will be described using examples.
[0044]
3A shows an example of the frequency distribution of the red primary color signal RI, FIG. 3B shows an example of the frequency distribution of the green primary color signal GI, and FIG. 3C shows the frequency of the blue primary color signal BI. It is a figure which shows distribution. 3A, 3B, and 3C, the horizontal axis indicates 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 (the blue primary color). The value of the signal BI), and the vertical axis indicates the frequency.
[0045]
The gradation information calculation circuit 5 in FIG. 1 calculates a luminance signal Y1 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.
[0046]
Y1 = α · RI + β · GI + γ · BI
In the above equation, α, β, and γ are predetermined coefficients.
[0047]
FIG. 4 is a histogram showing an example of the frequency distribution of the luminance signal Y1 calculated by the gradation information calculation circuit 5. The horizontal axis in FIG. 4 indicates the luminance level (value of the luminance signal Y1), and the vertical axis indicates the frequency. In the present embodiment, the luminance level has values “0” to “255”.
[0048]
In the example of FIG. 4, the frequency is 0 in the low range a and high range b. Therefore, the ranges a and b have a margin for performing the smoothing process by widening the luminance distribution.
[0049]
The cumulative frequency distribution creation circuit 50 of FIG. 2 calculates the cumulative frequency by sequentially calculating the frequency of each luminance level shown in FIG.
[0050]
FIG. 5 is a diagram showing an example of the cumulative frequency distribution RD created by the cumulative frequency distribution creation circuit 50. As shown in FIG. The horizontal axis in FIG. 5 indicates the luminance level (value of the luminance signal Y1), and the vertical axis indicates the cumulative frequency.
[0051]
In addition, the cumulative frequency distribution creation circuit 50 detects feature values such as the average value, mode value, minimum value, maximum value, deviation coefficient, white area, black area, etc. of the brightness level, and based on the detected feature values. A control value such as the maximum luminance level after normalization is calculated.
[0052]
Furthermore, the gain control circuit 60 generates an offset based on the correction gain limiting parameter GP.
[0053]
FIG. 6 is a diagram illustrating an example of the offset generated by the gain control circuit 60. The horizontal axis in FIG. 6 indicates the luminance level, and the vertical axis indicates the offset value.
[0054]
An example of the offset OF is indicated by a solid line, and another example of the offset OF is indicated by a broken line. The gain control circuit 60 increases the slope of the offset OF as shown by the solid line when the value of the correction gain restriction parameter GP is small, and as shown by the broken line when the value of the correction gain restriction parameter GP is large. Decrease the slope of the offset OF.
[0055]
The gain control circuit 60 performs the following processing for gain correction based on the correction gain restriction parameter GP.
[0056]
The gain control circuit 60 adds the offset OF shown in FIG. 6 to the cumulative frequency distribution RD shown in FIG. 5 to generate a corrected cumulative frequency distribution GR.
[0057]
FIG. 7 is a diagram illustrating an example of the corrected cumulative frequency distribution GR generated by the gain control circuit 60. The horizontal axis in FIG. 7 indicates the luminance level, and the vertical axis indicates the cumulative frequency.
[0058]
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.
[0059]
The normalization circuit 70 normalizes the corrected cumulative frequency distribution GR given from the gain control circuit 60 and creates a normalized cumulative frequency distribution SS. Specifically, the normalization circuit 70 performs a normalization operation on the corrected cumulative frequency distribution GR so that the maximum cumulative frequency of the normalized cumulative frequency distribution SS becomes the maximum luminance level obtained by the cumulative frequency distribution creation circuit 50. .
[0060]
FIG. 8 is a diagram illustrating an example of the normalized cumulative frequency distribution SS created by the normalization circuit 70. The horizontal axis in FIG. 8 indicates the luminance level, and the vertical axis indicates the normalized frequency.
[0061]
In FIG. 8, the normalized cumulative frequency distribution SS when the offset OF in FIG. 6 is large is indicated by a solid line, and the normalized cumulative frequency distribution SS when the offset OF in FIG. 6 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.
[0062]
As shown in FIG. 8, when the slope of the offset OF is large, that is, when the value of the correction gain limiting parameter GP is small, the displacement amount of the normalized cumulative frequency distribution SS with respect to the ramp line LP becomes small, and the slope of the offset OF Is small, that is, when the value of the correction gain limiting parameter GP is large, the displacement amount of the normalized cumulative frequency distribution SS with respect to the ramp straight line LP becomes large.
[0063]
The gradation correction conversion table creation circuit 12 in FIG. 1 calculates the correction amount ΔY by subtracting the ramp straight line LP from the normalized cumulative frequency distribution SS obtained by the normalization circuit 70.
[0064]
FIG. 9 is a diagram illustrating an example of the distribution of the correction amount ΔY calculated by the gradation correction conversion table creation circuit 12. In FIG. 9, the horizontal axis indicates the luminance level, and the vertical axis indicates the correction amount ΔY.
[0065]
In FIG. 9, the correction amount ΔY when the inclination of the offset OF in FIG. 6 is large is indicated by a solid line, and the correction amount ΔY when the inclination of the offset OF in FIG. 6 is small is indicated by a broken line.
[0066]
As shown in FIG. 8, when the inclination of the offset OF is large, that is, when the value of the correction gain restriction parameter GP is small, the correction amount ΔY is small, and when the inclination of the offset OF is small, that is, the correction gain restriction parameter GP. When the value of is large, the correction amount ΔY is large. Therefore, the correction gain is determined by the set value of the correction gain restriction parameter GP.
[0067]
The gradation correction conversion table creation circuit 12 has a look-up table (LUT) memory. The luminance signal Y1 is made to correspond to the address of the lookup table memory, and the correction amount ΔY is stored as data at that address. The correction amount ΔY stored in the look-up table memory constitutes a gradation correction conversion table. The gradation correction conversion table creation circuit 12 receives the luminance signal Y1 given via the switching circuit 11 during the vertical effective scanning period as an address signal, reads the correction amount ΔY from the designated address in the lookup table memory, and converts the conversion ratio. This is given to the calculation circuit 7.
[0068]
Next, the configuration and operation of the conversion ratio calculation circuit 7 will be described. FIG. 10 is a block diagram showing the configuration of the conversion ratio calculation circuit 7.
[0069]
10 includes an adding circuit 71 and a dividing circuit 72.
The adding circuit 71 adds the luminance signal Y1 given from the gradation information calculating circuit 5 in FIG. 1 and the correction amount ΔY given from the gradation correction conversion table creating circuit 12 to generate a corrected luminance signal Y2. To the division circuit 72.
[0070]
FIG. 11 is a diagram illustrating an example of the relationship between the luminance signal Y1 supplied to the adding circuit 71 and the corrected luminance signal Y2 generated by the adding circuit 71. In FIG. 11, the horizontal axis indicates the value of the luminance signal Y1, and the vertical axis indicates the value of the corrected luminance signal Y2.
[0071]
In the example of FIG. 11, when the value of the luminance signal Y1 is low, the corrected luminance signal Y2 has a lower value than the value of the luminance signal Y1, and when the luminance signal Y1 is high, the corrected luminance signal Y2 is The value is higher than the value of the luminance signal Y1.
[0072]
That is, when the value of the luminance signal Y1 is relatively low, the corrected luminance signal Y2 is smoothed to a range with a lower luminance level, and when the value of the luminance signal Y1 is relatively high, the corrected luminance signal Y2 is further increased in luminance level. Is smoothed to a high range.
[0073]
Subsequently, the division circuit 72 of FIG. 10 calculates a ratio between the given corrected luminance signal Y2 and the luminance signal Y1. The division circuit 72 divides the corrected luminance signal Y2 by the luminance signal Y1 to calculate a conversion ratio YR (= Y2 / Y1) for performing luminance distribution smoothing processing on the three digital primary color signals. The division circuit 72 gives the conversion ratio YR to the multiplication circuits 21, 22, and 23.
[0074]
The multiplier circuit 21 calculates the red primary color signal R0 using the conversion ratio YR (= Y2 / Y1) according to the following equation.
[0075]
R0 = (Y2 / Y1) .RI = YR.RI
Similarly, the multiplication circuit 22 and the multiplication circuit 23 calculate the green primary color signal G0 and the blue primary color signal B0 using the conversion ratio YR (= Y2 / Y1) according to the following equation.
[0076]
G0 = (Y2 / Y1) · GI = YR · GI
B0 = (Y2 / Y1) · BI = YR · BI
Next, the three digital primary color signals calculated by the above equation will be described. 12A shows an example of the frequency distribution of the red primary color signal R0, FIG. 12B shows an example of the frequency distribution of the green primary color signal G0, and FIG. 12C shows the frequency of the blue primary color signal B0. It is a figure which shows distribution. 12A, 12B, and 12C, the horizontal axis represents the red output luminance level (the value of the red primary color signal R0), the green output luminance level (the value of the green primary color signal G0), and the blue output luminance level (the blue primary color). The value of the signal B0), and the vertical axis indicates the frequency.
[0077]
In the frequency distribution of the red primary color signal R0 in FIG. 12A, the luminance distribution is expanded to a low range and a high range as compared with the frequency distribution of the red primary color signal RI in FIG. Therefore, it is possible to realize a high contrast of the red primary color signal R0 by the smoothing process of the red primary color signal RI.
[0078]
Similarly, in the frequency distribution of the green primary color signal G0 in FIG. 12B, the luminance distribution is expanded to a low range and a high range as compared with the frequency distribution of the green primary color signal GI in FIG. . Therefore, it is possible to realize high contrast of the green primary color signal G0 by smoothing the green primary color signal GI. Furthermore, in the frequency distribution of the blue primary color signal B0 in FIG. 12C, the luminance distribution is expanded to a low range and a high range as compared with the frequency distribution of the blue primary color signal BI in FIG. Therefore, high contrast of the blue primary color signal B0 can be realized by the smoothing process of the blue primary color signal BI.
[0079]
In the gradation correction apparatus 100 according to the present embodiment, the gradation information calculation circuit 5 includes three multiplication circuits, and the conversion ratio calculation circuit 7 includes one division circuit. The divider circuit can be realized with a circuit scale substantially equivalent to that of the multiplier circuit. Three multiplication circuits 21, 22, and 23 are used. That is, the gradation correction apparatus 100 includes a circuit corresponding to seven multiplication circuits. Therefore, in the gradation correction apparatus 100, the circuit scale is significantly reduced as compared with the conventional gradation correction circuit having 18 multiplication circuits.
[0080]
Further, since the luminance distribution is smoothed on each of the input red primary color signal RI, green primary color signal GI, and blue primary color signal BI, and color coordinate conversion and color inverse coordinate conversion are not performed, the calculation error is small. Deterioration of the image is prevented. Thus, in the gradation correction apparatus 100, it is possible to increase the contrast of the primary color signal without increasing the circuit scale and without causing image degradation.
[0081]
Further, since a plurality of primary color signals are multiplied by a common conversion ratio YR, the input red primary color signal RI, green primary color signal GI and blue primary color signal BI and the obtained red primary color signal R0, green primary color signal G0 and blue color are obtained. The change in color balance is less likely to occur with the primary color signal B0.
[0082]
In the present embodiment, the case where the luminance signal Y1 is calculated as the luminance correlation information from the red primary color signal RI, the green primary color signal GI, and the blue primary color signal BI by the gradation information calculation circuit 5 has been described. Alternatively, 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 and used as the luminance correlation information.
[0083]
In the present embodiment, the gradation information calculation circuit 5 corresponds to the luminance correlation information generation means, the luminance distribution extraction circuit 10 and the gradation correction conversion table creation circuit 12 correspond to the correction information generation means, and the conversion ratio calculation circuit 7 corresponds to the correction ratio calculation means, and the multiplication circuits 21, 22, and 23 correspond to the multiplication means. The multiplication circuit 21 corresponds to the first multiplication circuit, the multiplication circuit 22 corresponds to the second multiplication circuit, the multiplication circuit 23 corresponds to the third multiplication circuit, and the luminance distribution extraction circuit 10 detects the frequency distribution. The gradation correction conversion table creation circuit 12 corresponds to a correction information storage unit. Further, the correction amount ΔY corresponds to the correction information, the luminance signal Y1 corresponds to the luminance correlation information, and the conversion ratio YR corresponds to the correction ratio.
[0084]
【The invention's effect】
According to the present invention, the luminance distribution is smoothed based on correction information common to a plurality of primary color signals, so that the circuit scale can be reduced. In addition, since the luminance distribution is smoothed on each of the plurality of input primary color signals, the calculation error is small and the deterioration of the video is prevented. Therefore, it is possible to increase the contrast of the primary color signal without increasing the circuit scale and without causing deterioration of the image.
[0085]
Furthermore, since a plurality of primary color signals are multiplied by a common correction ratio, a change in color balance is unlikely to occur between the input primary color signals and the obtained primary color signals.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a gradation correction apparatus according to an embodiment of the present invention.
2 is a block diagram showing a configuration of a luminance distribution extraction circuit in FIG.
3A is a diagram illustrating an example of a frequency distribution of a red primary color signal, FIG. 3B is a diagram illustrating an example of a frequency distribution of a green primary color signal, and FIG. 3C is a diagram illustrating a frequency distribution of a blue primary color signal;
FIG. 4 is a histogram showing an example of a frequency distribution of a luminance signal calculated by a gradation information calculation circuit.
FIG. 5 is a diagram illustrating an example of a cumulative frequency distribution created by a cumulative frequency distribution creation circuit;
FIG. 6 is a diagram illustrating an example of an offset generated by a gain control circuit.
FIG. 7 is a diagram showing an example of a corrected cumulative frequency distribution generated by a gain control circuit.
FIG. 8 is a diagram showing an example of a normalized cumulative frequency distribution created by a normalization circuit
FIG. 9 is a diagram illustrating an example of a correction amount distribution calculated by a gradation correction conversion table creation circuit;
FIG. 10 is a block diagram illustrating a configuration of a conversion ratio calculation circuit.
FIG. 11 is a diagram illustrating an example of a relationship between a luminance signal given to an addition circuit and a corrected luminance signal generated by the addition circuit;
12A is a diagram illustrating an example of a frequency distribution of a red primary color signal, FIG. 12B is a diagram illustrating an example of a frequency distribution of a green primary color signal, and FIG. 12C is a diagram illustrating a frequency distribution of a blue primary color signal;
FIG. 13A is a diagram showing an example of a luminance frequency distribution in one frame before smoothing processing, and FIG. 13B is a luminance frequency distribution in one frame after smoothing processing by a conventional gradation correction apparatus. Illustration
[Explanation of symbols]
4 ₁ ~ 4 _n counter
5 Gradation information calculation circuit
7 Conversion ratio calculation circuit
10 Luminance distribution extraction circuit
11 Switching circuit
12 gradation correction conversion table creation circuit
21, 22, 23 multiplication circuit
100 gradation correction device
Y1, Y2 Luminance signal
ΔY Correction amount
YR conversion ratio
30 Address decoder
50 Cumulative frequency distribution creation circuit
60 Gain control circuit
70 Normalization circuit
71 Adder circuit
72 Division circuit
GP correction gain limit parameter
GR corrected cumulative frequency distribution
H ₁ ~ H _n frequency
P ₁ ~ P _n pulse
RD cumulative frequency distribution
SS Normalized cumulative frequency distribution
RI, R0 Red primary color signal
GI, G0 green primary color signal
BI, B0 Blue primary color signal

Claims (3)

Luminance correlation information generating means for generating luminance correlation information having correlation with luminance from a plurality of input primary color signals;
A cumulative frequency distribution unit that detects the frequency of appearance of each level of the luminance correlation information that is an output of the luminance correlation information generation unit for each frame and calculates the cumulative frequency distribution of the frequency of appearance;
A value at the minimum level of the luminance correlation information is a minimum value based on a preset correction gain restriction parameter, a value at the maximum level of the luminance correlation information is a maximum value, and the value of the luminance correlation information is taken. A gain control unit that generates a corrected cumulative frequency distribution by adding an offset value that is a monotonically increasing value with respect to the luminance correlation information within a possible range to a cumulative frequency distribution that is an output of the cumulative frequency distribution unit; and the gain control A frequency distribution detection means comprising: a normalization unit that performs a normalization operation on the basis of the maximum value of the corrected cumulative frequency distribution that is an output of the unit, and calculates a normalized cumulative frequency distribution;
The value at the minimum level of the luminance correlation information of the normalized cumulative frequency distribution that is the output of the frequency distribution detection means is the minimum value, the value at the maximum level of the luminance correlation information is the maximum value, and the luminance correlation information Correction information storage means for calculating, storing and outputting correction information for each level of the luminance correlation information by subtracting from the normalized cumulative frequency distribution a value that monotonically increases with respect to the luminance correlation information within a possible range of values When,
A correction ratio calculation means for setting a value obtained by dividing the addition result of the correction information and the luminance correlation information, which is an output of the correction information storage means, by the luminance correlation information as a correction ratio corresponding to the luminance correlation information;
Multiplying means for multiplying each of the inputted primary color signals by a correction ratio that is an output of the correction ratio calculating means;
A gradation correction apparatus having   The gradation correction apparatus according to claim 1, wherein the plurality of primary color signals include a red primary color signal, a green primary color signal, and a blue primary color signal.   The gradation correction apparatus according to claim 1, wherein the maximum value of the offset value increases as the value of the correction gain limiting parameter decreases.

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