JP2003299118A - Image quality correction circuit for display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit which can avoid variation of white balance even when an input brightness level or an average brightness level varies by performing individual image quality correction by signals R, G and B. <P>SOLUTION: A display rate to the input brightness level (or average brightness level) for each of signals R, G and B is varied to fix the average brightness level (or input brightness level), a correction curve using as a correction value a difference when each input brightness level (or average brightness level) is combined with the white balance for each fixed set value is found and previously stored in image quality correction value selection memories 13, 14 and 15 for the signals R, G and B, the correction value selected from the average brightness level of an input video signal and each signal R, G or B (input brightness level) after the gamma corrected is multiplied by the component of each signal after gamma corrected to adjust a gain. Consequently, even when the input and brightness levels vary, the white balance can be prevented from changing. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image quality correction circuit for individually performing image quality correction on R, G, and B signals in a display device such as a PDP or LCD.

[0002]

2. Description of the Related Art Generally, when a video signal is output to a display device such as a PDP or LCD, the image quality is corrected. In the conventional image quality correction, a correction curve is calculated based on the average luminance level of the input signal. Select this correction curve, R, G, B
All were switched to the same.

[0003]

The video signals are R, G,
When colors are reproduced by a combination of B signals and image quality correction is performed, it is desirable to perform correction for each of the R, G, and B signals, but conventionally, the correction curve used for correction is
Since the same R, G, and B signals are used, there is a problem that the white balance fluctuates when the input luminance level or the display rate changes.

According to the present invention, the image quality is corrected for each of the R, G and B signals individually, and the white balance does not change even if the input brightness level or the average brightness level changes, and the image quality correction of the display device does not occur. It is intended to provide a circuit.

[0005]

According to the present invention, an average luminance level calculation circuit 1 for calculating an average luminance level of an input video signal.
1, a gamma correction circuit 12 that outputs an input brightness level by performing gamma correction on an input video signal, a correction value for each average brightness level for adjusting white balance for each R, G, B signal, and each input brightness An R image quality correction value selection memory 13, a G image quality correction value selection memory 14, a B image quality correction value selection memory 15, which store correction values for the levels, and an R gain for adjusting the output gain using the correction values of these memories. The adjustment circuit 21, the G gain adjustment circuit 22, and the B gain adjustment circuit 23 are provided, and the R image quality correction value selection memory 13, the G image quality correction value selection memory 14, and the B image quality correction value selection memory 15 are R, With respect to each of G and B, when one of the average brightness level and the input brightness level is fixed, the white balance is adjusted for the other level. It is an image quality correction circuit of a display device according to claim in which the difference is stored as a correction value.

The R image quality correction value selection memory 13, the G image quality correction value selection memory 14, and the B image quality correction value selection memory 15 are
For each of R, G, and B, the display ratio with respect to the input luminance level (or average luminance level) is changed to fix the average luminance level (or input luminance level), and the input luminance is fixed for each fixed set value. Since the correction curve that stores the difference when the white balance is adjusted for the level (or the average brightness level) is stored, the white balance may change even if the input brightness level or the average brightness level changes. Disappears.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. First, the configuration of the present invention will be described with reference to FIG. The video signal input terminal 10 is connected to the average luminance level calculation circuit 11 and the gamma correction circuit 12. An R image quality correction value selection memory 13, a G image quality correction value selection memory 14, and a B image quality correction value selection memory 15 are connected in parallel to each other on the output side of the average brightness level calculation circuit 11. The output side of the gamma correction circuit 12 is also connected to the input sides of the R image quality correction value selection memory 13, the G image quality correction value selection memory 14, and the B image quality correction value selection memory 15. These R image quality correction value selection memory 13, G image quality correction value selection memory 14,
The output side of the B image quality correction value selection memory 15 is connected to the R gain adjusting circuit 21, the G gain adjusting circuit 22, and the B gain adjusting circuit 23, respectively, and the output side of the gamma correcting circuit 12 is also R side. The gain adjusting circuit 21, the G gain adjusting circuit 22, and the B gain adjusting circuit 23 are connected. The output gain is adjusted by the R gain adjusting circuit 21, the G gain adjusting circuit 22, and the B gain adjusting circuit 23, and the R output terminal 16, the G output terminal 17, and the B output terminal 18 are adjusted for each signal. Is output.

In the above-mentioned structure, the average brightness level calculation circuit 11 is for calculating and outputting the average brightness level for each frame, and the average brightness level is calculated by all pixels in one frame. For each pixel, and the total value divided by the total number of pixels is, for example, 32
The level is divided into stages and set. Information on the average brightness level is stored in the R image quality correction value selection memory 13,
It is input to the G image quality correction value selection memory 14 and the B image quality correction value selection memory 15. Here, the average brightness level is calculated in units of one frame, but the invention is not limited to this, and it can be calculated in any unit such as one field, one line, a plurality of lines, and a plurality of dots.

The gamma correction circuit 12 performs gamma correction on the values of the R, G, and B signals input from the video signal input terminal 10 and outputs the values (this is the input brightness level). The gamma value used at this time is appropriately set according to the display device. The input luminance level signals after the gamma correction are input to the R image quality correction value selection memory 13, the G image quality correction value selection memory 14, and the B image quality correction value selection memory 15, respectively.

The R image quality correction value selection memory 13, the G image quality correction value selection memory 14, and the B image quality correction value selection memory 15
Is for adjusting the white balance based on the average luminance level from the average luminance level calculation circuit 11 and the gamma-corrected R, G, and B signals (input luminance levels) output from the gamma correction circuit 12. Select and output the correction value.
Here, adjusting the white balance means R, G, B.
By setting the ratio of to a certain fixed value, this ratio becomes
It must be the same at low and high brightness levels. Therefore, it is necessary to adjust the white balance so that the relationship is not broken even if the brightness is changed. The correction value for adjusting this white balance is
It is necessary to store in advance in each image quality correction value selection memory for each R, G, B signal, and there are the following two methods for setting this correction value.

In the first method, while the average luminance level is fixed, the white balance is adjusted while changing the input luminance level, the difference generated at this time is used as a correction value to obtain a correction curve, and this is used as the total average. In this method, a correction curve for the brightness level is stored in each image quality correction value selection memory. The second method is to adjust the white balance while changing the average brightness level with the input brightness level fixed, and obtain a correction curve using the difference generated at this time as a correction value, and calculate this for all input brightness levels. This is a method of storing the correction curve in each image quality correction value selection memory. Hereinafter, a method of setting these two correction values will be described in detail. In the present embodiment, the input brightness level is 00
The average brightness level is 0 in 256 steps from h to FFh.
Although the case where there are 32 stages of 31 has been described, it is not limited to this, and it goes without saying that more or less stages may be set.

(1) Fixing Average Brightness Level to Match White Balance First, fixing the average brightness level is achieved by changing the display rate with respect to the input brightness level. Here, as shown in FIG. 3, the display rate refers to the ratio of the lit pixels of all the pixels of the display panel. When the input brightness level is increased, the display rate is decreased to When lowering the luminance level, the average luminance level is fixed to a constant value by increasing the display rate. For example, when the white balance is adjusted while fixing the average brightness level to 16 out of 32 levels, the reference pattern as shown in FIG. 3 is output and displayed on the display device, and the input brightness levels are changed while changing the display rate. The white balance is adjusted while measuring the brightness for each of R, G, and B with a chromaticity meter.
Then, a difference appears for each of R, G, and B, and this difference is set as a correction value for each of R, G, and B. The relationship between the input brightness level and the white balance difference (correction value) at the average brightness level 16 is shown in FIG. 4, and the correction curves shown in FIG. In advance, it is stored in the ROM or the like. This correction curve is obtained for all average brightness levels in the ROM
It is possible to select an appropriate correction value for all the inputs by storing it in the etc. Note that the contents programmed by software are executed to change the area ratio of the reference pattern as shown in FIG. 3 for changing the display ratio.

From the correction curve thus stored,
A correction value suitable for the average brightness level and the input brightness level is R,
The image quality correction value selection memories 13, 14 and 15 for G and B are selected, and using these correction values, the R gain adjustment circuit 21, the G gain adjustment circuit 22 and the B gain adjustment circuit 2 in the subsequent stage are used.
In step 3, the input luminance level after gamma correction is multiplied, and the output gain is adjusted. After the gain adjustment is performed in this way, the signals are output from the R output terminal 16, the G output terminal 17, and the B output terminal 18. Note that FIG. 2A shows the relationship between the input luminance level and the corrected output after the gain adjustment.

In the above method, the average brightness level is kept constant, the white balance is adjusted for each input brightness level while changing the input brightness level and the display ratio of the panel, and the correction curve is set. However, the white balance may be adjusted for a plurality of input brightness levels, an approximate curve may be obtained from the values, and this may be used as a correction curve. The approximate curve thus obtained is stored in advance in the R image quality correction value selection memory 13, the G image quality correction value selection memory 14, and the B image quality correction value selection memory 15, respectively, so that an appropriate correction value for input can be obtained. Can be selected.

(2) When the input luminance level is fixed and the white balance is adjusted The input luminance level is fixed by changing the display rate with respect to the average luminance level. The input luminance level is fixed to a constant value by increasing the display rate when increasing the average luminance level and decreasing the display rate when decreasing the average luminance level. For example, if the input brightness level is 2
When adjusting the white balance while fixing the value to 64 in 56 steps, the reference pattern as shown in FIG. 3 is output and displayed on the display device, and the average luminance level is changed by the chromaticity meter while changing the display rate. The white balance is adjusted while measuring the brightness for each of R, G, and B. Then, a difference appears for each of R, G, and B, and this difference is set as a correction value for each of R, G, and B. The relationship between the average brightness level and the white balance difference (correction value) at the input brightness level 64 is shown in FIG. 5, and the correction curves shown in FIG. In advance, it is stored in the ROM or the like. By obtaining this correction curve for all input luminance levels and storing it in the ROM or the like, it becomes possible to select appropriate correction values for all inputs. Note that the contents programmed by software are executed to change the area ratio of the reference pattern as shown in FIG. 3 for changing the display ratio.

From the correction curve thus stored,
A correction value suitable for the average brightness level and the input brightness level is selected in each image quality correction value selection memory, and this correction value is set in the subsequent R
The gain adjustment circuit 21 for G, the gain adjustment circuit 22 for G, and the gain adjustment circuit 23 for B respectively perform a process of multiplying the gamma-corrected input luminance level to adjust the output gain. After the gain adjustment is performed in this way, the signals are output from the R output terminal 16, the G output terminal 17, and the B output terminal 18.

In the above method, the input brightness level is kept constant, the white balance is adjusted for each average brightness level while changing the average brightness level and the display ratio of the panel, and the correction curve is set. The white balance is not limited to the above, but the white balance may be adjusted for a plurality of average brightness levels, an approximate curve may be obtained from the value, and this may be used as the correction curve. The approximate curve thus obtained is stored in advance in the R image quality correction value selection memory 13, the G image quality correction value selection memory 14, and the B image quality correction value selection memory 15, respectively, so that an appropriate correction value for input can be obtained. Can be selected.

In the above-described embodiment, the output after gamma correction is adjusted in gain using the selected correction value and output, and the input brightness level and the correction output are curved even at a sufficiently low brightness level. It corresponds finely to the correction curve. However, as shown in FIG. 2B, when the input brightness level is lower than a certain value, the effect of the image quality correction is not clearly shown. Instead of using the correction curve, the correction line 19 obtained by performing a linear approximation to the origin from the output value after gamma correction at that value may be used as the correction output for the input luminance level, and the gain adjustment may not be performed. As a specific configuration in this case, as shown in FIG. 6, the R output switching is provided at the subsequent stage of the R gain adjusting circuit 21, the G gain adjusting circuit 22, and the B gain adjusting circuit 23 in the circuit of FIG. Circuit 24, G output switching circuit 25, B
Output switching circuits 26 for each are provided. The R output switching circuit 24, the G output switching circuit 25, and the B output switching circuit 26 include a correction line 19 obtained by performing a linear approximation to the origin from the output value after the gamma correction when the input brightness level is a certain value or less.
Is stored in the internal memory as a correction output for the input luminance level. In such a configuration, when the R, G, and B signals after gamma correction are input to the R output switching circuit 24, the G output switching circuit 25, and the B output switching circuit 26, respectively, the video signal It is determined whether or not the input luminance level is higher than a certain value. When the input luminance level is higher than a certain value, the signals from the R, G, and B gain adjusting circuits 21, 22, and 23 are output, and there is the input luminance level of the video signal. In the vicinity of the origin which is equal to or less than the value, the correction line 19 obtained by linearly approximating the internal memory is selected, and the signal from each gain adjusting circuit is switched and output. This makes it possible to omit the process of adjusting the gain.

Further, when the input brightness level is lower than a certain value, the effect of the image quality correction is not clearly shown. Therefore, as shown in FIG. 2A, when the input brightness level is lower than a certain value. Alternatively, the horizontal line 20 that holds the output after gamma correction at a constant value may be used as the gamma correction output, and the subsequent gain adjustment may not be performed. Also in this case, similarly, in the circuit configuration as shown in FIG. 6, the R output switching circuit 24, the G output switching circuit 25, and the B output switching circuit 2
In 6, a horizontal line 20 in which the output after gamma correction when the input brightness level is less than a certain value is held at a constant value is stored in an internal memory as a correction output for the input brightness level. Then, the R output switching circuit 24, the G output switching circuit 25, and the B output switching circuit 26, when the input luminance level of the video signal is equal to or higher than a certain value, the R, G, and B gain adjustment circuits 21, 22, The signal from 23 is output, and in the vicinity of the origin where the input brightness level of the video signal is less than a certain value, the correction horizontal line 20 of the internal memory is selected, and the signal from each gain adjustment circuit is switched and output. This makes it possible to omit the process of adjusting the gain.

[0020]

According to the invention described in claim 1, R, G,
Since the gain adjustment is performed by selecting the correction value for adjusting the white balance from the correction curve set individually for each signal of B, the white balance changes even if the input brightness level and the average brightness level change. Never.

According to the second aspect of the present invention, the R image quality correction value selection memory 13, the G image quality correction value selection memory 14, and the B image quality correction value selection memory 15 have the input brightness level for each of R, G, and B. Since the average luminance level is fixed by changing the display ratio for, and the correction curve having the difference when the white balance is adjusted for each fixed setting value as the correction value is stored, By selecting the correction value according to the change in the input brightness level and the average brightness level, the white balance does not change.

According to the third aspect of the present invention, the R image quality correction value selection memory 13, the G image quality correction value selection memory 14, and the B image quality correction value selection memory 15 have the input brightness level for each of R, G, and B. The average luminance level is fixed by changing the display ratio for, and an approximate correction curve with the difference when the white balance is adjusted for a plurality of input luminance levels for each fixed setting value as the correction value is stored. Therefore, by selecting the correction value from the approximate correction curve according to the change in the input brightness level and the average brightness level, similar image quality correction can be performed even with the approximate correction curve, and the white balance does not change.

According to the fourth aspect of the present invention, the R image quality correction value selection memory 13, the G image quality correction value selection memory 14, and the B image quality correction value selection memory 15 have the average brightness level for each of R, G, and B. The input luminance level is fixed by changing the display ratio for, and the correction curve having the correction value as the difference when the white balance is adjusted for each average luminance level for each of the fixed setting values is stored. By selecting the correction value according to the change in the input brightness level and the average brightness level, the white balance does not change.

According to the fifth aspect of the present invention, the R image quality correction value selection memory 13, the G image quality correction value selection memory 14, and the B image quality correction value selection memory 15 have the average brightness level for each of R, G, and B. The input luminance level is fixed by changing the display ratio for, and an approximate correction curve having the correction value as the difference when the white balance is adjusted for a plurality of average brightness levels for each fixed setting value is stored. Therefore, by selecting the correction value from the approximate correction curve according to the change in the input brightness level and the average brightness level, similar image quality correction can be performed even with the approximate correction curve, and the white balance does not change.

According to the sixth aspect of the invention, when the input luminance level is less than a certain value, a linear approximation is performed from the value after gamma correction at that time to the origin, and this is used as a correction output. In this part, the process of adjusting the gain can be omitted.

According to the invention of claim 7, when the input luminance level is below a certain value, the value after gamma correction at that time is held at a constant value and this is used as a correction output. In the part, the process of performing the gain adjustment can be omitted.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an image quality correction circuit of a display device according to the present invention.

FIG. 2A is an image quality correction curve diagram showing a corrected output after gain adjustment with respect to an input luminance level, and FIG.
It is the figure which showed the handling method at the input brightness level below a certain value in (a).

FIG. 3 is an explanatory diagram of a reference pattern in the case where the display ratio is changed and adjusted in the circuit of the present invention.

FIG. 4 is a correction curve showing a relationship between an input luminance level and a white balance difference (correction value) when the average luminance level is fixed and the input luminance level and the display rate are changed to adjust the white balance. It is a figure.

FIG. 5 is a correction curve showing the relationship between the average brightness level and the white balance difference (correction value) when the input brightness level is fixed and the average brightness level and the display ratio are changed to adjust the white balance. It is a figure.

FIG. 6 is a block diagram showing another embodiment of the image quality correction circuit of the display device according to the present invention.

[Explanation of symbols]

10 ... Video signal input terminal, 11 ... Average brightness level calculation circuit, 12 ... Gamma correction circuit, 13 ... R image quality correction value selection memory, 14 ... G image quality correction value selection memory, 15 ... B image quality correction value selection memory, 16 ... R output terminal, 17 ... G output terminal, 18 ... B output terminal, 19 ... Correction line, 20 ... Horizontal line,
21 ... R gain adjusting circuit, 22 ... G gain adjusting circuit, 23 ... B gain adjusting circuit, 24 ... R output switching circuit, 25 ... G output switching circuit, 26 ... B output switching circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/36 G09G 3/36 (72) Inventor Shuji Shuji 1116 Suenaga, Takatsu-ku, Kawasaki-shi, Kanagawa Stock company In Fujitsu General (72) Inventor Junichi Onodera 1116 Suenaga, Takatsu-ku, Kawasaki-shi, Kanagawa Stock company, Fujitsu General F-term (reference) 5C006 AA01 AA11 AA22 AF06 AF13 AF44 AF45 AF46 AF51 AF53 AF54 BC16 BF02 FA56 5C066 AA03 BA20 CA08 EA02 EC01 GA01 GB01 KA12 KE05 KE09 KM13 KM15 LA02 5C080 AA05 AA10 BB05 CC03 DD01 EE19 EE29 GG08 GG09 GG12 GG15 GG17 JJ02 JJ05

Claims (7)

[Claims] 1. An average luminance level calculation circuit 11 for calculating an average luminance level of an input video signal, a gamma correction circuit 12 for performing gamma correction on the input video signal and outputting the input luminance level, and R, G, and B respectively. An R image quality correction value selection memory 13, a G image quality correction value selection memory 14, and a B image quality correction value selection memory that store a correction value for each average brightness level for adjusting the white balance for each signal and a correction value for each input brightness level. 15 and an R gain adjusting circuit 21, a G gain adjusting circuit 22, and a B gain adjusting circuit 23 that adjust the output gain using the correction values of these memories, and the R image quality correction value selecting memory 13 , G image quality correction value selection memory 14 and B image quality correction value selection memory 15 are R,
For each of G and B, one of the average brightness level and the input brightness level is fixed, and the difference when white balance is adjusted for the other level is stored as a correction value. Display device image quality correction circuit. 2. An average brightness level calculation circuit 11 for calculating an average brightness level of an input video signal, a gamma correction circuit 12 for performing gamma correction on the input video signal and outputting the input brightness level, and R, G, B respectively. R image quality correction value selection memory 1 that stores a correction value for adjusting the white balance for each signal
3, G image quality correction value selection memory 14, B image quality correction value selection memory 15, and R gain adjustment circuit 21, G gain adjustment circuit 22, and B gain that adjust the output gain using the correction values of these memories. Adjusting circuit 23, and R
Image quality correction value selection memory 13, G image quality correction value selection memory 1
4, the B image quality correction value selection memory 15 fixes the average brightness level by changing the display rate with respect to the input brightness level for each of R, G, and B, and whites each input brightness level for each of the fixed setting values. An image quality correction circuit for a display device, which stores a correction curve having a difference when a balance is made as a correction value. 3. An average brightness level calculation circuit 11 for calculating an average brightness level of an input video signal, a gamma correction circuit 12 for applying an gamma correction to the input video signal and outputting the input brightness level, R, G and B respectively. R image quality correction value selection memory 1 that stores a correction value for adjusting the white balance for each signal
3, G image quality correction value selection memory 14, B image quality correction value selection memory 15, and R gain adjustment circuit 21, G gain adjustment circuit 22, and B gain that adjust the output gain using the correction values of these memories. Adjusting circuit 23, and R
Image quality correction value selection memory 13, G image quality correction value selection memory 1
4, the B image quality correction value selection memory 15 fixes the average brightness level by changing the display rate with respect to the input brightness level for each of R, G, and B, and sets a plurality of input brightness levels for each of the fixed set values. An image quality correction circuit for a display device, which stores an approximate correction curve with a difference when the white balance is adjusted as a correction value. 4. An average brightness level calculation circuit 11 for calculating an average brightness level of an input video signal, a gamma correction circuit 12 for applying an gamma correction to the input video signal and outputting an input brightness level, R, G and B respectively. R image quality correction value selection memory 1 that stores a correction value for adjusting the white balance for each signal
3, G image quality correction value selection memory 14, B image quality correction value selection memory 15, and R gain adjustment circuit 21, G gain adjustment circuit 22, and B gain that adjust the output gain using the correction values of these memories. Adjusting circuit 23, and R
Image quality correction value selection memory 13, G image quality correction value selection memory 1
4, the B image quality correction value selection memory 15 fixes the input brightness level by changing the display ratio with respect to the average brightness level for each of R, G, and B, and whites the average brightness level for each of the fixed setting values. An image quality correction circuit for a display device, which stores a correction curve having a difference when a balance is made as a correction value. 5. An average brightness level calculation circuit 11 for calculating an average brightness level of an input video signal, a gamma correction circuit 12 for performing gamma correction on the input video signal and outputting the input brightness level, R, G and B respectively. R image quality correction value selection memory 1 that stores a correction value for adjusting the white balance for each signal
3, G image quality correction value selection memory 14, B image quality correction value selection memory 15, and R gain adjustment circuit 21, G gain adjustment circuit 22, and B gain that adjust the output gain using the correction values of these memories. Adjusting circuit 23, and R
Image quality correction value selection memory 13, G image quality correction value selection memory 1
4. The B and B image quality correction value selection memory 15 fixes the input brightness level by changing the display rate with respect to the average brightness level for each of R, G, and B, and the average brightness level of a plurality of units for each of the fixed set values. An image quality correction circuit for a display device, which stores an approximate correction curve with a difference when the white balance is adjusted as a correction value. 6. An R output switching circuit 24, a G output switching circuit 25, and a B output switching circuit 26 are provided after the R gain adjusting circuit 21, the G gain adjusting circuit 22, and the B gain adjusting circuit 23. The R output switching circuits 24 and G are provided respectively.
The R, G, and B signals after gamma correction are input to the output switching circuit 25 for B and the output switching circuit 26 for B respectively, and when the input luminance level of the video signal is equal to or higher than a certain value, When a signal is output and the input brightness level of the video signal is near a certain value or less near the origin, linear approximation is performed from that value after gamma correction to the origin, and the linear approximation signal of this gamma correction value is adjusted for each gain. 6. The signal of the circuit is switched and output.
An image quality correction circuit for the display device described. 7. An R output switching circuit 24, a G output switching circuit 25, and a B output switching circuit 26 are provided after the R gain adjusting circuit 21, the G gain adjusting circuit 22, and the B gain adjusting circuit 23, respectively. The R output switching circuits 24 and G are provided respectively.
The R, G, and B signals after gamma correction are input to the output switching circuit 25 for B and the output switching circuit 26 for B respectively, and when the input luminance level of the video signal is equal to or higher than a certain value, When a signal is output and the input brightness level of the video signal is near the origin below a certain value, the value after gamma correction of that value is held as a constant value, and this constant value signal of the gamma correction value is output to each gain adjustment circuit. 6. The image quality correction circuit for a display device according to claim 1, wherein the image quality correction circuit outputs the signal by switching it.