JPH11296149A - Digital gamma correction method and liquid crystal device using the same - Google Patents

Abstract

(57) [Problem] To provide a high-accuracy, high-speed, low-cost digital gamma correction method and a liquid crystal device using the same. According to the present invention, the driving voltage-transmittance characteristic of the liquid crystal panel is switched between a simple characteristic and a precisely approximated detailed characteristic as necessary, and gamma correction data is calculated using the characteristic, and written into a gamma correction LUT.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a digital gamma correction method and a liquid crystal device using the same.

[0002]

2. Description of the Related Art FIG. 16 shows a conventional example of a digital gamma correction method and a liquid crystal device, and FIG. 2 shows an example of a drive voltage-transmittance characteristic (VT characteristic) of a liquid crystal panel 4. In the following description, the digital video data 100 and the corrected digital video data 101 are both 256-level data of 0 to 255 levels.

The LUT 1 is a look-up table that performs a predetermined gamma correction on the digital video data 100 and outputs corrected digital video data 101.

Generally, in the VT characteristic of the liquid crystal panel 4, the relationship between the drive voltage and the transmittance is not linear as shown in FIG. Therefore, when the input digital video data 100 is directly converted from digital to analog and the liquid crystal panel 4 having the VT characteristic is driven, the relationship between the digital video data 100 and the transmittance of the liquid crystal panel 4 is shown in FIG. As shown in the figure, it becomes non-linear, and in particular, 1
The change in transmittance per gradation becomes small, and the display quality of the liquid crystal display image is significantly deteriorated. Therefore, it is necessary to correct the digital video data 100 so that the digital video data 100 and the transmittance of the liquid crystal panel 4 have a linear relationship.

FIG. 18 shows the driving voltage range of the liquid crystal panel 4 as an example of gamma correction data stored in the LUT 1.
3 shows gamma correction data in the case of between V2 and V3 in FIG. By converting the digital video data 100 using the LUT 1 storing the gamma correction data, the digital video data 100 and the transmittance of the liquid crystal panel 4 have a linear relationship as shown in FIG. The gamma correction data stored in the LUT 1 is measured in advance and stored in the ROM
(Read-Only Memory) 6 based on the VT characteristic data of the liquid crystal panel 4 stored in the CPU (Central Process).
ing Unit) 5 performs a predetermined calculation and sets the value.

The correction digital signal 101 is a DAC (Dig
The digital-to-analog conversion is performed by an ital-Analog Converter 2 and an analog video signal 102 as shown in FIG.
Becomes Further, the variable amplifying unit 7 alternately performs inversion amplification and non-inversion amplification every horizontal period, and adds the offset voltage Voff and the common electrode voltage Vcom of the liquid crystal panel 4 to obtain a liquid crystal drive signal 103 as shown in FIG. Is input to the liquid crystal panel 4.

A switching signal 1 for switching the functions of brightness adjustment, contrast adjustment, and color temperature adjustment is provided to the CPU 5.
04, a pulse-like up signal 105 for increasing an adjustment value for each adjustment content in a predetermined step,
A pulse-like down signal 106 to be decreased is input.

When brightness adjustment is selected by the switching signal 104 and the up signal 105 is input,
The Voff shown in FIG. 3 is increased by increasing the offset voltage of the variable amplifier 7 according to the number of pulses or the pulse width of the input up signal 105, and the voltage applied to the liquid crystal panel 4 is shifted to the higher voltage side. By shifting, the brightness of the displayed image is increased. When contrast adjustment is selected and the up signal 105 is input, the amplification degree of the variable amplifying unit 7 is increased according to the number of input up signal pulses or the pulse width to be applied to the liquid crystal panel 4. The contrast is increased by enlarging the voltage width.

FIG. 19 shows another conventional example.

The difference from the conventional example shown in FIG. 16 is that the digital video data 100 is
1 and 2 in that the data is corrected in each case, and that the analog video signal 102 is amplified by the amplification unit 3 with a predetermined amplification factor. The linear conversion data as shown in FIG. 20 is stored in the LUT 8 for level conversion. For example, the conversion data is stored as shown in FIG. By changing, the drive voltage range of the liquid crystal panel 4 is controlled.
Note that the gamma correction data stored in the LUT 1 is shown in FIG.
However, there is no need to change them by brightness adjustment, contrast adjustment, and color temperature adjustment. Other operations and functions are the same as those of the conventional example shown in FIG.

[0011]

In the conventional example shown in FIG. 16, for example, when the contrast is increased, the amplification degree of the variable amplifying unit 7 is increased to expand the driving voltage range of the liquid crystal panel 4. For this reason, the drive voltage range assumed by the gamma correction data written in the LUT 1 does not match the actual drive voltage range, and there is a problem that sufficient gamma correction is not performed particularly in the low gradation region and the high gradation region. Have.

On the other hand, in the conventional example shown in FIG.
Since the gamma correction data set at T1 and the voltage range applied to the liquid crystal panel by the amplifying unit 3 are fixed, the above-described problem does not occur, but a memory having approximately twice the capacity must be prepared. In addition, there is a problem that the liquid crystal device becomes expensive and the integration of the circuit is hindered, and it is difficult to reduce the size of the liquid crystal device.

[0013]

According to a first aspect of the present invention, there is provided a digital gamma correction method, wherein a gradation of a digital video signal is obtained in accordance with gamma correction data generated by using a simple characteristic which approximately approximates a driving voltage-transmittance characteristic of a liquid crystal panel. A simple mode for converting the driving voltage of the liquid crystal panel and a detailed mode for converting the gradation of the digital video signal according to the gamma correction data generated using the detailed characteristics precisely approximated the transmittance characteristics, The simple mode and the detailed mode are appropriately switched.

According to the above configuration, when performing image quality adjustment such as brightness adjustment, contrast adjustment, and color temperature adjustment, the simple mode and the detailed mode are switched according to the processing speed required at each time, and the gamma correction data is adjusted. Performing the change processing has an effect of achieving both high-speed processing and high image quality.

A digital gamma correction method according to a second aspect is characterized in that the simple characteristic of the drive voltage-transmittance characteristic of the liquid crystal panel is approximated by a plurality of straight lines.

According to the above digital gamma correction method, R
The drive voltage-transmittance characteristics data of the liquid crystal panel stored in the OM can be reduced, and the characteristics can be stored in the working RAM (Ra).
Since the arithmetic processing for reproducing the data on an ndom-access memory or the like is simple, high-speed processing can be performed.

According to a third aspect of the present invention, in the digital gamma correction method, the detailed characteristics of the drive voltage-transmittance characteristic of the liquid crystal panel are approximated by at least one curve or at least one curve and at least one straight line. Features.

According to the above digital gamma correction method,
When approximating the drive voltage-transmittance characteristics of a liquid crystal panel in detail, by separating the section where straight line approximation is possible and the section where curve approximation is performed, a relatively simple curve approximation formula can be used in the curve approximation section. Therefore, the data of the drive voltage-transmittance characteristic of the liquid crystal panel stored in the ROM can be reduced, and the arithmetic processing for reproducing the characteristic in the working RAM or the like is simpler than the approximation accuracy, and This has the effect of enabling high-speed processing.

According to a fourth aspect of the present invention, there is provided a liquid crystal device, comprising: a look-up table for correcting gradation data of a digital video signal;
A DA converter that receives the output of the look-up table and converts the output to an analog signal, an amplifier that amplifies the output of the DA converter with a predetermined amplification, adds a predetermined offset voltage, and drives a liquid crystal panel; A ROM storing a detailed characteristic that approximately approximates the drive voltage-transmittance characteristic of the liquid crystal panel and a simple characteristic that approximately approximates the drive voltage-transmittance characteristic of the liquid crystal panel, and the simple characteristic, or A gamma correction data is calculated using the detailed characteristics, and the CPU stores the gamma correction data in the look-up table.

According to the above liquid crystal device, when image quality adjustment such as brightness adjustment, contrast adjustment and color temperature adjustment is performed, depending on the processing speed required at each time,
By switching between a detailed characteristic in which the drive voltage-transmittance characteristic of the liquid crystal panel is approximately approximated and a simple characteristic in which the drive voltage-transmittance characteristic of the liquid crystal panel is approximately approximated, reading from the ROM and changing the gamma correction data are performed. This has the effect of achieving both high-speed processing and high image quality.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a diagram showing a gamma correction method according to the present invention and a first embodiment of a liquid crystal device using the same, and FIG. FIG. 4 is a diagram illustrating an example of a transmittance characteristic (VT characteristic). In the following description, the digital video signal 100 is changed from 0 to 2
55 levels of 256 gradations, corrected digital video signal 101
Are 512 gradations from 0 to 511 levels. Further, in the liquid crystal panel 4 of the present embodiment, as shown in FIG. 2, as the driving voltage is increased, the transmittance is increased. On the contrary, as the driving voltage is increased, the transmittance is decreased. It is the same regardless of the type.

The digital video data 100 undergoes a predetermined gamma correction by the LUT 1, and is input to the DAC 2 as corrected digital video data 101. DAC2
Converts the corrected digital video data 101 from digital to analog, and outputs an analog video signal 102 shown in FIG. The amplifying unit 3 alternately performs inversion amplification and non-inversion amplification of the analog video signal 102 for each horizontal period, and sends a liquid crystal driving signal 103 obtained by adding the offset voltage Voff and the common electrode voltage Vcom of the liquid crystal panel 4 to the liquid crystal panel 4. Output.

The gamma correction data stored in the LUT 1 is measured in advance, and based on the VT characteristic data of the liquid crystal panel 4 stored in the ROM 6, the digital video data 1
00 and the transmittance of the liquid crystal panel 4 have a linear relationship.
Set by PU5.

In FIG. 4, as an example of the gamma correction data stored in the LUT 1, the driving voltages of the liquid crystal panel 4 when the value of the digital video data 100 is 0 and 255 are V2 and V3 shown in FIG. 7 shows gamma correction data in the case. LU storing this gamma correction data
By converting the digital video data 100 by T1, the digital video data 100 and the transmittance of the liquid crystal panel 4 have a proportional relationship as shown in FIG.

FIGS. 6, 7, and 8 show the driving voltage range of the liquid crystal panel 4 between V1 and V3, between V2 and V4, and V1 respectively.
−V4, and the gamma characteristic data corresponding to each drive voltage range is stored in the LUT1.
, The digital video data 100 and the transmittance of the liquid crystal panel 4 have a proportional relationship as shown in FIG.

The drive voltage range of the liquid crystal panel 4 includes a switching signal 104 for switching functions of brightness adjustment, contrast adjustment, and color temperature adjustment, and a pulse-like up signal for increasing the adjustment value of each adjustment content in a predetermined step. 105 and the pulse-like down signal 10 to be reduced
6 is input to the CPU 5 and is changed by performing a process corresponding to each function.

For example, if the current driving voltage range is V2-V3
In order to increase the brightness by adjusting the brightness, the liquid crystal driving voltage range V2-V3 may be shifted to the higher voltage side by a required amount, and the gamma correction data corresponding to the shift may be calculated and stored in the LUT1. If the liquid crystal drive voltage range after the shift is V2'-V3 ', the required gamma correction data is as shown in FIG.

In order to increase the contrast by adjusting the contrast, for example, the drive voltage range is expanded to V1-V4, and gamma correction data as shown in FIG.

Generally, there are cases where the setting / change of the gamma correction data as described above is necessary, in a case where the initial setting of the liquid crystal device is performed, and in a case where a change request of the liquid crystal device observer is made. The former is often performed when the power of the display device is turned on, and the time required for setting may be relatively long in many cases. However, in the latter case, the observer often makes a change request while observing the display, so that the time required for the change is required to be short.

This will be described by taking brightness adjustment as an example. An observer continuously changes the brightness, for example, outputs the up signal 105 by operating a brightness adjustment button or the like provided on the surface of the liquid crystal device. In the case of setting the brightness, if the time required to change the gamma correction data is long, the operation of pressing the button and the observed image quality are not easily linked, and it may be difficult to adjust to the desired brightness.

Therefore, considering the operability of the observer, the shorter the processing time required for changing the gamma correction data, the better. However, if this processing time is considered too important, it is not possible to perform detailed gamma correction requiring complicated calculations, and it is not possible to obtain sufficient image quality.

Therefore, in the present embodiment, high-precision and high-speed image quality control is realized by devising the VT characteristic data of the liquid crystal panel stored in the ROM 6 and the processing thereof.

In the ROM 6, the VT characteristic of the liquid crystal panel 4 is divided into a plurality of regions as shown in FIG. 10, and each region is approximated by a straight line. Is precisely approximated using a straight line or a curve.
Stores T characteristic data.

Although the number of divisions of the region and the boundary value of the region vary depending on the characteristics of the liquid crystal panel 4 and the approximation method described later, in this embodiment, since the corrected digital video data 101 has 512 gradations, the actual V The division number, boundary value, and approximate expression of the area are selected so that the error between the −T characteristic and the detailed VT characteristic is within about 0.2% corresponding to one gradation. Further, as for the simple VT characteristic, since the digital video data 100 has 256 gradations, it is sufficient if the digital video data 100 is within about 0.4% corresponding to one gradation. If the load on the amount is large, the allowable range of the approximation error may be expanded to reduce the number of divided regions.

Each region in FIG. 10 and regions 1, 3, 5 in FIG.
Is approximated by a mathematical expression represented by T = a × V + b.
In regions 2 and 4, T = a × V ＾ 3 + b × V ＾ 2 + c × V
+ D or T = a × V ＾ b + c. (However, a, b, c, and d are constants determined for each area.) If necessary, the number of divisions of the area may be changed, or the areas 2, 3, and 4 in FIG. Or the area 3 may be further divided and approximated by a plurality of straight lines.

The data actually stored in the ROM 6 is the boundary data of each divided area, the parameters of each straight line, and each curve. As a result, the simple VT characteristic and the detailed VT characteristic
Even if one is prepared, the capacity required for the ROM 6 is relatively small.

Next, the operation of the CPU 5 will be described with reference to FIG. When the switching signal 104, the up signal 105, and the down signal 106 are input and it becomes necessary to change the gamma correction data, the processing of the CPU 5 proceeds according to the flowchart shown in FIG. Hereinafter, a case where the brightness adjustment is selected by the switching signal 104 and the up signal 105 is input will be described as an example, but the same applies to a case where the contrast adjustment and the color temperature adjustment are selected and a case where the down signal 106 is input. It is.

First, the up signal 105 is analyzed, and either the simple mode or the detailed mode is set. Specifically, as shown in FIGS. 13 and 14, high-speed processing is required when the up signal 105 is continuously input for a predetermined time T1 or more or continuously input at time intervals within the predetermined time T2. Is determined as the simple mode, and if not, the detailed mode is set. The predetermined times T1 and T2 are appropriately set in consideration of the operability of the liquid crystal device, the processing capability of the CPU, and the like.

Next, the setting of the drive voltage range of the liquid crystal panel 4 is changed according to the set operation mode. Specifically, in the detailed mode, the drive voltage range is changed to the higher voltage side with one gradation equivalent of 512 gradations as a basic step,
In the simple mode, the drive voltage range is changed to the higher voltage side with two or more gradations as basic steps.

In the simple mode, first, the parameters of the simple VT characteristic are read from the ROM 6, the simple VT characteristic is reproduced in the working RAM in the CPU 5, and the gamma correction data is determined in accordance with the previously determined drive voltage range. Is calculated, and LUT1 is calculated.
To be stored.

On the other hand, in the detailed mode, similarly to the simple mode, the parameters of the detailed VT characteristics are read from the ROM 6 to reproduce the detailed VT characteristics in the work RAM in the CPU 5, and the drive voltage range determined in advance is determined. The gamma correction data is calculated according to the formula (1), and stored in the LUT1. The working RAM for reproducing the simple VT characteristic and the detailed VT characteristic is CP
A RAM provided separately from U5 may be used.

Here, the simple mode emphasizes high-speed processing and makes it easy for the observer to perform an image quality changing operation. Therefore, it is difficult to realize high-quality display. Therefore, as shown in FIG. 15, when the time interval at which the up signal 105 is input becomes longer than T2, or when a continuous signal ends and no new signal is input during T2, the high-speed It is determined that the processing has become unnecessary, the drive voltage range set last in the simple mode is maintained, and the detailed mode is executed to execute the detailed gamma correction. .

As described above, in this embodiment, the simple VT characteristic and the detailed VT characteristic are prepared as the VT characteristic data of the liquid crystal panel, and a request for changing brightness, contrast, or color temperature is issued. If there is, by using two VT characteristics depending on the required processing speed,
High-precision, high-speed image quality control is realized.

Further, these two VT characteristic data are:
By dividing the VT characteristic curve into a plurality of regions and extracting each boundary data, each straight line, and each curve parameter,
The memory required for holding can be saved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of the present invention shown in a first embodiment.

FIG. 2 is a diagram showing an example of a VT characteristic of a liquid crystal panel 4.

FIG. 3 is a diagram showing a waveform example of an analog video signal.

FIG. 4 is a diagram showing an example of gamma correction data.

FIG. 5 is a diagram showing a relationship between digital video data and transmittance of the liquid crystal panel 4.

FIG. 6 is a diagram showing an example of gamma correction data.

FIG. 7 is a diagram showing an example of gamma correction data.

FIG. 8 is a diagram showing an example of gamma correction data.

FIG. 9 is a diagram showing an example of gamma correction data.

FIG. 10 is a diagram showing an example of dividing a VT characteristic.

FIG. 11 is a diagram showing an example of division of a VT characteristic.

FIG. 12 illustrates an operation of the CPU 5.

FIG. 13 is a diagram illustrating determination of an operation mode.

FIG. 14 is a view for explaining determination of an operation mode.

FIG. 15 is a diagram illustrating determination of an operation mode.

FIG. 16 is a diagram showing a conventional example.

FIG. 17 shows a conventional example of digital video data and a liquid crystal panel 4.
FIG. 4 is a diagram showing a relationship between transmittances of the light emitting elements.

FIG. 18 is a diagram showing a relationship between digital video data and corrected digital video data in a conventional example.

FIG. 19 is a diagram showing another conventional example.

FIG. 20 is a diagram showing an example of data stored in a level conversion LUT.

FIG. 21 is a view showing an example of data stored in a level conversion LUT.

FIG. 22 is a diagram showing an example of data stored in a level conversion LUT.

FIG. 23 is a view showing an example of data stored in a level conversion LUT.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 LUT 2 DAC 3 Amplification part 4 Liquid crystal panel 5 CPU 6 ROM 7 Variable amplification part 8 Level conversion LUT

Claims (4)

[Claims] 1. A simple mode for converting a gradation of a digital video signal in accordance with gamma correction data generated using a simple characteristic that approximately approximates a drive voltage-transmittance characteristic of a liquid crystal panel; A digital mode having a detailed mode for converting the gradation of a digital video signal in accordance with gamma correction data generated by using detailed characteristics that precisely approximate a rate characteristic, wherein the simple mode and the detailed mode are appropriately switched. Gamma correction method. 2. The digital gamma correction method according to claim 1, wherein the simple characteristics of the drive voltage-transmittance characteristics of the liquid crystal panel are approximated by a plurality of straight lines. 3. The liquid crystal panel according to claim 1, wherein the detailed characteristics of the drive voltage-transmittance characteristics of the liquid crystal panel are approximated by at least one curve or at least one curve and at least one straight line. Digital gamma correction method. 4. A look-up table for correcting gradation data of a digital video signal, a DA converter receiving an output of the look-up table and converting the output to an analog signal, and amplifying an output of the DA converter with a predetermined amplification factor. And an amplifier for adding a predetermined offset voltage to drive the liquid crystal panel, and a detailed characteristic precisely approximating a drive voltage-transmittance characteristic of the liquid crystal panel and a drive voltage-transmittance characteristic of the liquid crystal panel. A liquid crystal display comprising: a ROM that stores approximated simple characteristics; and a CPU that calculates gamma correction data using the simple characteristics or the detailed characteristics according to an image quality adjustment signal and stores the gamma correction data in the look-up table. apparatus.