JP2006163290A - Image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal image display apparatus capable of controlling brightness without causing deterioration in gradation. <P>SOLUTION: The image display apparatus comprises an effective driving voltage range variable means of display elements, a γ-correction LUT having γ-correction data expressing a maximum driving voltage range of the display elements by the number of input bits to a D-A converter, + n bits, a 1st calculating means for converting an input image signal into an input gradation of the γ-correction LUT corresponding to an effective driving voltage range of the display elements, and a 2nd calculating means for making a γ-correction LUT output match with the input gradation to the D-A converter. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to luminance control and γ correction processing on a display screen of a liquid crystal display element.

  In general, the liquid crystal display element has a non-linear characteristic as shown in FIG. 5 as an example of the transmittance characteristic (hereinafter referred to as VT characteristic) of the liquid crystal display element with respect to the driving voltage level. Therefore, in order to display with good gradation in the liquid crystal display element, it is necessary to perform correction to match this VT characteristic with the linear characteristic, which is generally called γ correction.

  As a γ correction circuit, digital γ correction using a look-up table (hereinafter referred to as LUT) method has been the mainstream since good correction accuracy can be obtained.

  When the γ correction is performed with 10 bits, the correction data of the γ correction LUT is, for example, the minimum drive voltage Va when the effective drive voltage range is between the points Va and Vb in the VT characteristic shown in FIG. 0, the maximum drive voltage Vb is 1023, and the drive voltage is expressed as a 10-bit digital value. The minimum transmittance Ta corresponding to the minimum drive voltage Va is 0, the maximum transmittance Tb is 1023, and the transmittance is 10-bit digital. It is expressed by a value and prepared so that a change in transmittance Ta-Tb with respect to a change in input voltage between Va and Vb has a linear characteristic.

  The digital image data subjected to the γ correction processing by the γ correction LUT is converted into an analog signal by the D / A converter and applied to the liquid crystal display element as an effective drive voltage. The number of output bits of the γ correction LUT corresponds to the number of input bits of the D / A converter. Here, an example in which a 10-bit D / A converter is used is shown.

  By the way, as a display device, it is necessary to perform brightness control such as display brightness and contrast adjustment or white balance adjustment according to the user's preference. This luminance control is to control the transmittance of the liquid crystal display element, for example, to set the transmittance at the maximum input signal to Tc in FIG.

  There are two methods for controlling the transmittance. First, the effective driving voltage range Va-Vb of the liquid crystal display element is fixed, for example, digital operation is performed on the digital image data so that the driving voltage of the maximum input signal changes from Vb to Vc. The second is a method of changing the amplitude of the drive signal, and the second is a method of changing the effective drive voltage range of the liquid crystal display element itself from Va-Vb to Va-Vc without changing the digital image data.

  In the first method, since the effective drive voltage range of the liquid crystal display element is fixed, the γ correction data prepared in advance in the γ correction LUT does not deviate from the effective drive voltage range.

  However, for example, when the adjustment is performed to increase the contrast by 0.8, even if a 1023-level maximum image signal is input as a 10-bit digital image signal, the signal is converted to an 818-level signal by digital calculation. That is, an image that was displayed with 1024 gradations before the adjustment is displayed with 819 gradations after the contrast adjustment of 0.8 times, and the gradation width is reduced.

  In the second method, the digital image data is left as it is, and the effective drive voltage range of the liquid crystal display element is made variable according to the brightness control such as contrast adjustment. Does not occur.

  However, since the effective drive voltage range of the liquid crystal display element is changed, the drive voltage range of the correction data prepared in the γ correction LUT is not matched and accurate γ correction cannot be performed.

  In order to solve the above problem, it is optimal to reproduce γ correction data corresponding to the setting of the effective driving voltage range of the liquid crystal display element from the γ correction data reproduction data stored in the ROM and store it in the γ correction LUT. Some perform gamma correction (see, for example, Patent Document 1).

In addition, without the γ correction LUT, the upper and lower reference voltages of the D / A converter are controlled to vary the effective drive voltage range of the liquid crystal display element, and the D / A conversion characteristics are controlled non-linearly. Some perform gamma correction (see, for example, Patent Document 2).
JP-A-11-296149 JP 2001-350450 A

  In both of the conventional examples described above, it is possible to perform γ correction optimal for the effective drive voltage range of the liquid crystal display element. However, in the first conventional example, there is a problem that the processing for reproducing the γ correction LUT data is necessary, so that the circuit scale increases and the processing for rewriting the γ correction table takes time.

  Further, in the second conventional example described above, detailed description for controlling the D / A conversion characteristic is not made, but there is information for controlling the D / A conversion characteristic nonlinearly according to γ correction. There is a problem of how to control the information with respect to changes in the effective voltage range.

  The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a liquid crystal image display apparatus capable of performing luminance control without causing gradation deterioration.

  In order to solve this problem, an image display device according to the present invention includes an effective driving voltage range variable means for a display element, and a γ correction in which the maximum driving voltage range of the display element is expressed by the number of input bits of the D / A converter + n bits. A γ correction LUT having data, a first computing means for converting an input image signal into an input gradation of the γ correction LUT corresponding to the effective drive voltage range of the display element, and a γ correction LUT output of the D / A converter And a second calculation means for matching the input gradation.

  The effect | action by the said problem-solving means is as follows.

  That is, γ correction data representing the maximum drive voltage range of the display element in terms of the number of input bits of the D / A converter + n bits is provided, and γ correction data corresponding to the effective drive voltage range is used among the γ correction data. An operation is performed on the input image signal, and an operation is performed so that the γ correction LUT output matches the input gradation of the D / A converter.

  That is, even when image display is performed using a part of the maximum drive voltage range as the effective drive voltage range in order to perform luminance control, the input image signal is once converted to a number of gradations larger than the number of gradations of the input image signal, After γ correction is performed using the optimal γ correction range, gradation deterioration can be prevented by converting to the input gradation of the D / A converter.

  As described above, by using the image display device according to the present invention, even when the effective driving voltage range of the display element is arbitrarily set, luminance control with optimum γ correction is performed without causing gradation deterioration. I can do it.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic block diagram showing a first embodiment of an image display apparatus according to the present invention.

  In FIG. 1, 10 is a first computing means, 20 is a γ correction LUT, 30 is a second computing means, 40 is a D / A converter, 50 is an effective driving voltage range varying means, 60 is a liquid crystal display element, 70 Is a control means.

  Here, the γ correction LUT 20 has γ correction data in which the maximum drive voltage range of the liquid crystal display element 60 is expressed by the number of input bits of the D / A converter 40 + n bits.

  That is, in the liquid crystal display element having the VT characteristic shown in FIG. 2A, the input voltage Vmin−Vmax in a range where the VT characteristic is not saturated is set as the maximum drive voltage range of the liquid crystal display element 60, and D / A Assuming that the number of input bits of the converter is 10 bits, it has the γ correction data shown in FIG. 2B generated as 2048 gradations between the input voltage Vmin and Vmax and between the transmittance Tmin and Tmax at the input voltage.

  In the above configuration, the control unit 70 sets the effective driving voltage range for the liquid crystal display element 60 by controlling the effective driving voltage range varying unit 50 according to contrast and brightness adjustment or white balance adjustment. Further, the first calculation means 10 and the second calculation means 30 are controlled to obtain an optimum γ using γ correction data in a range corresponding to the execution drive voltage range from γ correction data prepared in the γ correction LUT 20. Make corrections.

  For example, the minimum voltage of the effective drive voltage range of the liquid crystal display element is set to Vmin, the maximum voltage is set to Vt corresponding to 0.8 times the maximum drive voltage range Vmin−Vmax, and the γ correction LUT input range at this time is 0− 1637, and the corresponding γ correction LUT output range is 0 to 1554.

  Accordingly, the 1024 gradations of the input image signal correspond to the input gradation of the γ correction LUT = 1638, and the output gradation of the γ correction LUT = 1555 corresponds to the input gradation of the D / A converter = 1024.

  That is, assuming that the input image signal is Vsig1 and the γ correction LUT output signal is Vsig2, the calculation of the expression (1) is performed in the first calculation means, and the calculation of the expression (2) is performed in the second calculation means.

Equations (1) and (2) are
(1638/1024) × Vsig1 (1)
(1024/1555) × Vsig2 (2)
It becomes.

  In the above control, when the minimum voltage in the effective driving voltage range of the liquid crystal display element is set to Vb corresponding to 5% of the maximum driving voltage range Vmin−Vmax, the maximum voltage becomes Vt ′ = Vt + (Vb−Vmin), and γ correction is performed. Assume that the LUT input range is 102-1739, and the γ correction LUT output range is 495-1615.

  Accordingly, 1024 gradations of the input image signal are made to correspond to the input gradation = 1638 of the γ correction LUT, the offset 102 is added, and the output gradation = in contrast to the γ correction LUT output signal minus the output offset 495. 1121 corresponds to the input gradation of the D / A converter = 1024.

  That is, the calculation of the expression (3) is performed in the first calculation means, and the calculation of the expression (4) is performed in the second calculation means.

Equations (3) and (4) are
(1638/1024) × Vsig1 + 102 (3)
(1024/1121) × (Vsig2−495) (4)
It becomes.

  In the above example, if the number of gradations of the γ correction LUT output is larger than the number of gradations of the input image signal indicated by 10 bits = 1024 gradations, it can be considered that there is no gradation deterioration due to digital calculation.

  As described above, according to the present embodiment, it is possible to selectively use the γ correction data without causing gradation deterioration in accordance with the effective driving voltage range of the liquid crystal display element. Optimal γ correction can be performed corresponding to the control. Therefore, it is possible to provide a liquid crystal image display device that can perform luminance control without causing gradation deterioration.

  Further, for example, by setting Vb−Vt ′ described above as the effective driving voltage range of the liquid crystal display element in the standard contrast and brightness setting, it is possible to set the contrast and brightness adjustment range with the optimum γ correction. I can do it. In the present embodiment, the γ correction LUT data is described as having 11 bits = 2048 gradations, which is 1 bit plus the number of bits of the D / A converter = 10, but the number of bits to be added is It is not limited to 1.

(Second Embodiment)
FIG. 3 is a schematic block diagram showing a second embodiment of the image display apparatus according to the present invention. The same components as those in FIG.

  In FIG. 3, reference numeral 51 denotes a reference voltage generation unit of the D / A converter 40 controlled by the control unit 70.

  The control means 70 adjusts the output level and amplitude of the D / A converter 40 so that the effective drive voltage range of the liquid crystal display element 60 is a drive voltage range corresponding to the contrast or brightness adjustment of the image display device.

  Corresponding to the adjustment of the output level and amplitude of the D / A converter 40, the first calculation means 10 and the second calculation means 30 are controlled by the control means 70 so as to operate in the same manner as in the first embodiment. Be controlled.

  As described above, according to the present embodiment, it is possible to provide a liquid crystal image display device capable of performing luminance control without causing gradation deterioration as in the first embodiment.

(Third embodiment)
FIG. 4 is a schematic block diagram showing a third embodiment of the image display apparatus according to the present invention. The same components as those in FIG.

  In FIG. 4, 52 is a reference voltage generating means of a D / A converter built in the liquid crystal display element 61 controlled by the control means 70, 61 is a liquid crystal display element for inputting an image signal as digital data, Built-in A converter.

  According to the present embodiment, as in the second embodiment, the control unit 70 causes the internal effective drive voltage range of the liquid crystal display element 61 to be a drive voltage range corresponding to the contrast or brightness adjustment of the image display device. The output level and amplitude of the internal AD / A converter of the liquid crystal display element 61 are adjusted.

  Corresponding to the adjustment of the output level and amplitude of the internal D / A converter of the liquid crystal display element 61, the first calculation means 10 and the second calculation means 30 operate in the same manner as in the first embodiment. Are controlled by the control means 70.

  As described above, according to the present embodiment, it is possible to provide a liquid crystal image display device capable of performing luminance control without causing gradation deterioration as in the first embodiment.

1 is a schematic block diagram showing a first embodiment of an image display device of the present invention. It is a figure which shows the example of (gamma) correction data of this invention. It is a schematic block diagram which shows 2nd Embodiment of the image display apparatus of this invention. It is a schematic block diagram which shows 3rd Embodiment of the image display apparatus of this invention. It is a figure which shows the VT characteristic example of a liquid crystal display element.

Explanation of symbols

10 First computing means 20 γ correction LUT
30 Second calculation means 40 D / A converter 50 Effective drive voltage range variable means 60 Liquid crystal display element 70 Control means

Claims (3)

  An effective drive voltage range variable means for the display element, a γ correction LUT having γ correction data representing the maximum drive voltage range of the display element by the number of input bits of the D / A converter + n bits, and an input image signal of the display element First computing means for converting the input gradation of the γ correction LUT corresponding to the effective driving voltage range, and second computing means for matching the γ correction LUT output with the input gradation of the D / A converter. An image display device characterized by things.   The effective driving voltage range variable means of the display element varies the voltage level and amplitude of the output of the D / A converter by changing the reference voltage of the D / A converter, thereby changing the effective driving voltage range of the display element. The image display device according to claim 1, wherein:   An effective driving voltage range variable means for the display element, a display element for inputting an image signal as digital data, and a γ having γ correction data representing the maximum driving voltage range of the display element by the number of input bits of the display element + n bits A correction LUT, first calculation means for converting an input image signal into an input gradation of a γ correction LUT corresponding to an effective drive voltage range of the display element, and a γ correction LUT output to match the input gradation of the display element An image display device comprising: a second computing unit.

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