Television – Image signal processing circuitry specific to television – Gray scale transformation
Reexamination Certificate
1998-08-11
2001-08-28
Hsia, Sherrie (Department: 2614)
Television
Image signal processing circuitry specific to television
Gray scale transformation
C348S572000
Reexamination Certificate
active
06281944
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a technique of correcting for a non-linear characteristic in a display device, and more particularly to an apparatus and method that is adapted to compensate for a non-linear characteristic in a flat display device, such as a liquid crystal panel, in which an image signal is processed in a digital system and driven with an analog signal.
2. Description of the Prior Art
Recently, a flat panel display device has been developed and spread as a picture display device. Such a flat display device requires that, although picture elements(or pixels) are driven with an analog signal like a liquid crystal panel or a plasma display panel, an image signal to be applied to each pixel should be processed in a digital system. Also, the plat display device is unable to perform an electro-light conversion in the same shape as an electrical signal like the existing cathode ray tube. In other words, the flat display device generates a light signal changing non-linearly with respect to an image signal changing linearly. For example, in the case of a liquid crystal panel, a light quantity transmitting the liquid crystal panel responds non-linearly to an image signal changing linearly. The flat display device having such a non-linear characteristic referred to as a gamma error has a disadvantage in that it has a low picture quality. In order to overcome this disadvantage, a display apparatus employing the flat display device includes circuits for compensating for a non-linear characteristic in the flat display device.
FIG. 1
shows a conventional liquid crystal display apparatus having a gamma correction function. As shown in
FIG. 1
, the liquid crystal display apparatus includes an analog to digital converter
110
, hereinafter referred to as “A-D converter”, receiving an analog image signal, and a first memory
120
, a digital signal processor(DSP)
130
, a second memory
140
, a digital to analog converter
150
, hereinafter referred to as “D-A converter”, and a liquid crystal panel driver
160
that are connected, in series, to the A-D converter
110
. The A-D converter
110
converts an analog image signal into an 8 bit digital image signal. The digital image signal generated from the A-D converter
110
are temporarily stored in the first memory
120
. The DSP
130
converts the digital image signal stored in the first memory
120
into an image signal having such a shape that is required by a flat display device, i.e., a liquid crystal panel. In other words, a shape of the digital image signal stored in the first memory
120
is converted to meet a driving condition of the liquid crystal panel by means of the DSP
130
. The second memory
140
compensates for a gamma error of the digital image signal shape-converted by means of the DSP
130
, that is, a non-linear characteristic of the liquid crystal panel. More specifically, the second memory
140
generates a compensating image signal having a gray scale different from the digital image signal from the DSP
130
. In order to perform such a gamma compensation of the digital image signal, a look-up table, in which compensating logical values correspond to each of logical values(i.e., 256 logical values) in a digital image signal, is stored in the second memory
140
. Accordingly, the digital image signal acts as an address signal of the second memory
140
. Also, a part of the logical values of the compensating image signal output from the second memory
140
corresponds commonly to at least two logical values in the logical values of the digital image signal. The compensating image signal output from the second memory
140
is converted into a shape of analog signal by means of the A-D converter
150
. Then, the liquid crystal driver
160
drives a liquid crystal panel(not shown) with an output signal of the D-A converter
150
.
The liquid crystal display apparatus in
FIG. 1
further includes a timing controller
170
and a data controller
180
that are controlled by a system controller
190
. The timing controller
170
divides operation timing of the A-D converter
110
, the first memory
120
, the DSP
130
, the second memory
140
, the D-A converter
150
and the liquid crystal panel driver
160
. The data controller
180
controls a timing of a signal applied from the liquid crystal panel driver
160
to the liquid crystal panel.
In the liquid crystal display apparatus using such a look-up table, a gray scale of the compensating image signal becomes smaller than that of the digital image signal. In other words, when the digital image signal has a 8 bit, the gray scale of the compensating image signal becomes smaller than 256 steps which are a gray scale of the digital image signal having 256 steps. Due to this, a gamma compensating apparatus using the look-up table lowers a gray scale of the image signal applied to the liquid crystal panel driver
160
. As a result, the number of colors that can be displayed on the flat display device is reduced.
FIG. 2
shows a liquid crystal display apparatus having a gamma correction function of analog system. As shown in
FIG. 2
, the liquid crystal display apparatus includes a AD converter
210
for converting an analog image signal into a digital image signal, and a memory
220
, a DSP
230
, a D-A converter
240
, a gamma corrector
250
and a flat panel driver
260
that are connected, in series, to the A-D converter
210
. The memory
220
temporarily stores the digital image signal applied from the A-D converter
210
. The DSP
230
converts the digital image signal stored in the memory
220
into an image signal having such a shape that is required by a flat display device(not shown), i.e., a liquid crystal panel. In other words, a shape of the digital image signal stored in the first memory
220
is converted to meet a driving condition of the flat display device by means of the DSP
230
. The shape-converted digital image signal is applied to the gamma corrector
250
after the compensating image signal was converted into a shape of analog signal by means of the D-A converter
240
. The gamma corrector
250
amplifies the analog image signal by a different gain in accordance with a level of the analog image signal from the D-A converter
240
, thereby compensating a non-linear characteristic of the liquid crystal panel, that is, a gamma error. Then, the flat panel driver
260
drives the flat display device with the compensated analog image signal.
The flat display apparatus in
FIG. 2
further includes a timing controller
270
and a gain controller
280
that are controlled by means of a system controller
290
. The timing controller
270
divides an operation timing of each of the A-D converter
210
, the memory
220
, the DSP
230
and the gamma corrector
250
. The gain controller
280
controls an amplification factor of the gamma corrector under the system controller
290
. To this end, the gain controller
290
divides voltage levels of an analog image signal into a number of level areas and has gain values given to each level area. The gamma corrector
250
, in which an amplification factor is controlled by means of the gain controller
280
, includes a plurality of amplifiers having a different amplification factor in response to each level area of the analog image signal or a non-linear amplifier having a variable amplification factor.
In the flat display apparatus having a gamma correction function of analog system as described above, since an analog image signal is compensated by means of the plurality of amplifiers having a different amplification factor or the non-linear amplifier, a non-linear characteristic, that is, a gamma error of the flat display device can not be compensated accurately. Also, in the flat display apparatus having a gamma correction function of analog system, it is difficult to control a gain of an amplifier, so that it causes the reduced productivity as well as a different picture quality for each product.
In view of this, there is required an apparatus and method that
Fleshner & Kim LLP
Hsia Sherrie
LG Electronics Inc.
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