This application claims the priority benefit of Taiwan application serial no. 98105256, filed on Feb. 19, 2009. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of specification.
1. Field of the Invention
The present invention relates to a gamma voltage generator.
2. Description of Related Art
Along with the development of electronic technologies, products related to digital display and image processing techniques have been widely used. Besides, because a digital signal processor (DSP) offers a high calculation speed, the enhancement of image brightness is usually performed in a display panel (for example, a liquid crystal display (LCD) panel) by multiplying an input pixel data by a specific floating-point multiple to generate a corresponding output pixel data.
However, regardless of whether the relationship between the input pixel data Di
In other words, the conventional gamma voltage generating apparatus 200 can only generate a gamma voltage corresponding to a digital output pixel data, and the digital output pixel data can only be an integer within a specific range due to the limitation of the bit number of the digital system. For example, if the output pixel data has 8 bits, the output pixel data can only be an integer between 0 and 255.
In addition, the following situation will be produced if an image is processed regarding some specific characteristic thereof (for example, the brightness or contrast of the image is changed). Referring to
It can be well understood from the example described above that such a conversion and rounding action may cause the grayscale 35 to disappear. This is due to the limitation in the structures of the existing circuit and DAC. As a result, image and color distortion may be caused.
Accordingly, the present invention is directed to a gamma voltage generator which adjust and generate an interpolated gamma output voltage dynamically corresponding to a floating-point grayscale data.
The present invention is further directed to a gamma voltage generating apparatus which divides an interpolated gamma output voltage to generate a plurality of divided interpolated gamma output voltages.
The present invention provides a gamma voltage generator including an operation amplifier, a first reference impedance unit, a second reference impedance unit, a first variable impedance unit, a second variable impedance unit, and a select unit. The operation amplifier has a first input terminal, a second input terminal, and an amplified output terminal, wherein the amplified output terminal generates an amplified output voltage. The first reference impedance unit has one terminal for receiving a first gamma voltage and another terminal coupled to the first input terminal of the operation amplifier. The second reference impedance unit has one terminal for receiving a second gamma voltage and another terminal coupled to the second input terminal of the operation amplifier. The first variable impedance unit is coupled between the first input terminal and the amplified output terminal of the operation amplifier and provides a first variable impedance. The second variable impedance unit is coupled between the second input terminal of the operation amplifier and one terminal of the first reference impedance unit and provides a second variable impedance. The select unit is coupled to the operation amplifier and selects the amplified output voltage or the first gamma voltage according to a control signal to generate an interpolated gamma output voltage.
The present invention further provides a gamma voltage generating apparatus including a plurality of gamma voltage generators and a plurality of voltage dividing elements. Each of the gamma voltage generators includes an operation amplifier, a first reference impedance unit, a second reference impedance unit, a first variable impedance unit, a second variable impedance unit, and a select unit. The operation amplifier has a first input terminal, a second input terminal, and an amplified output terminal, wherein the amplified output terminal generates an amplified output voltage. The first reference impedance unit has one terminal for receiving one of a plurality of gamma voltages and another terminal coupled to the first input terminal of the operation amplifier. The second reference impedance unit has one terminal for receiving another one of the gamma voltages and another terminal coupled to the second input terminal of the operation amplifier. The first variable impedance unit is coupled between the first input terminal and the amplified output terminal of the operation amplifier and provides a first variable impedance. The second variable impedance unit is coupled between the second input terminal of the operation amplifier and one terminal of the first reference impedance unit and provides a second variable impedance. The select unit is coupled to the operation amplifier and selects the amplified output voltage or the first gamma voltage according to a control signal to generate an interpolated gamma output voltage. In addition, the voltage dividing elements are sequentially connected in series between the terminals of the gamma voltage generators for generating the interpolated gamma output voltages and generate a plurality of divided interpolated gamma output voltages.
As described above, present invention provides the variable impedance unit, the reference impedance unit and the amplifier for generating an interpolated gamma output voltage by performing an interpolation calculation to two different gamma voltages. Thereby, interpolated gamma output voltages corresponding to floating-point grayscale data can be generated. Accordingly, the resolution of grayscale voltages supplied to a display is increased and image distortion is reduced.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
V
mk=(Vm+1−Vm)(mk−m)+Vm (1)
The gamma voltage Vm is generated by a digital-to-analog converter (DAC) 211 in the gamma voltage generator 200 illustrated in
V
m+1
=A
m(Vm−VP)+VP (2)
In foregoing expression (2), Am is the divide ratio of the resistor string composed of the resistors R1˜Rn, and which can be expressed as:
The following expression can be obtained by bringing foregoing expression (2) into foregoing expression (1):
V
mk
=A
mk(Vp−Vm)+Vm (4)
wherein Amk=(1−Am)(mk−m).
It can be understood from foregoing expression (4) that the gamma voltage Vmk corresponding to the pixel data grayscale mk can be obtained by multiplying the difference between the gamma voltage Vm and the gamma voltage Vp by a specific multiple Amk and then adding the gamma voltage Vm to the obtained product.
The potential difference between the first input terminal TN and the second input terminal TP of the operation amplifier 410 is close to zero, and in the present embodiment, it is assumed that the impedances provided by the reference impedance units 420 and 430 are both Ra and the variable impedances provided by the variable impedance units 440˜450 are both Rb. Thus, the relationship between the first gamma voltage Vm, the second gamma voltage VP, and the amplified output voltage Vo1 can be obtained through a voltage division formula as:
It should be mentioned that Ra/Rb in foregoing expression (5) is equal to Amk in foregoing expression (4).
In addition, foregoing assumption that the impedances provided by the reference impedance units 420 and 430 are both Ra and the variable impedances provided by the variable impedance units 440˜450 are both Rb is only an example used herein for simplifying the expression (5) but not for limiting the scope of the present invention. Herein, the impedances provided by the reference impedance units 420 and 430 may also be different, and the variable impedances provided by the variable impedance units 440 and 450 may also be different.
The select unit 460 is coupled to the operation amplifier 410 and receives the first gamma voltage Vm and the amplified output voltage Vo1. The select unit 460 determines whether to transmit the gamma voltage Vm or the amplified output voltage Vo1 according to a control signal CTRL so as to generate an interpolated gamma output voltage Vmk. The select unit 460 is disposed because the amplified output voltage Vo1 generated by the operation amplifier 410 based on foregoing expression (5) cannot be equal to the gamma voltage Vm. Thus, when the gamma voltage generated corresponding to the pixel data grayscale is equal to the gamma voltage Vm, the gamma voltage Vm can be selected according to the control signal CTRL and output as the interpolated gamma output voltage Vmk by the select unit 460.
In order to allow those having ordinary knowledge in the art to better understand the present embodiment, an actual example of the present embodiment will be described below with reference to
Referring to
It should be mentioned that the relationships between the reference impedance units 420 and 430 and the variable impedance units 440 and 450 can be adjusted by using a control circuit 470 with calculation ability. The control circuit 470 adjusts the relationships between the reference impedance units 420 and 430 and the variable impedance units 440 and 450 by adjusting the variable impedances provided by the variable impedance units 440 and 450. The control circuit 470 may have following calculation rules.
A corresponding resistor selection is output according to the product of an input pixel data and a specific multiple (the multiplication can be carried out by a digital circuit). Namely, a database (or lookup table) is established based on different resistor selections corresponding to the products of different pixel data and different multiples, and a desired resistor selection is then obtained according to the product of an input pixel data and a specific multiple.
A corresponding resistor selection is output according to an input pixel data and a specific multiple (no multiplication is carried out). Namely, a table of different resistor selections corresponding to different pixel data and different multiples is established, and once a pixel data and a multiple are input, the desired resistor selection can be obtained by looking up the table according to the input pixel data and multiple.
A resistor selection is directly output according to a multiple. In other words, different resistor selection is selected according to different multiple regardless of what the pixel data is.
Different resistor selection is selected according to different image characteristic (for example, brightness, contrast, or other characteristics of an image, and the image characteristic can be obtained through existing hardware or software techniques such as statistics, probability, image processing, or mathematics). For example, different resistor selections are output corresponding to images having different brightness, contrast, color distribution, and spectrum distribution, etc.
The aforementioned multiple refers to the slope of a gamma conversion curve.
Thus, the visual effect of an image can be dynamically and precisely changed through such dynamic resistor switching and control mechanism. However, the technique provided by the present invention may also be turned off, namely, the original gamma voltage corresponding to each grayscale is changed.
In the present embodiment, the variable impedance unit 540 includes N switches SW21˜SW2N and N impedance elements R11˜R1N, wherein N is a positive integer. Each of the impedance elements (for example, R11) and each of the switches (for example, SW21) are connected in series between one and another terminal of the variable impedance unit 540. The variable impedance provided by the variable impedance unit 540 can be dynamically changed through different on/off states of the switches SW21˜SW2N. It should be noted that in order to avoid an infinite impedance provided by the variable impedance unit 540 (open circuit), at least one of the switches SW21˜SW2N has to be turned on.
Similarly, the variable impedance unit 550 includes M switches SW11˜SW1M and N impedance elements R21˜R2M, wherein M is a positive integer. Each of the impedance elements (for example, R21) and each of the switches (for example, SW11) are connected in series between one and another terminal of the variable impedance unit 550. The variable impedance provided by the variable impedance unit 550 can be dynamically changed through different on/off states of the switches SW11˜SW1M. It should be noted that in order to avoid an infinite impedance provided by the variable impedance unit 550 (open circuit), at least one of the switches SW11˜SW1M has to be turned on.
In addition, the select unit 560 is composed of select switches ENS1 and ENS4. One terminal of the select switch ENS1 receives the first gamma voltage Vm, and the other terminal thereof is coupled to the connect switch ENS2. The terminal of the connect switch ENS2 which is not coupled to the select switch ENS1 is coupled to the amplified output terminal of the operation amplifier 510. Only one of the select switches ENS1 and ENS4 can be turned on, namely, the select switches ENS1 and ENS4 cannot be turned on together.
When the select switch ENS1 is turned on while the select switch ENS4 is turned off, the gamma voltage generator 500 directly outputs the first gamma voltage Vm, and accordingly the connect switches ENS2 and ENS3 are turned off.
Similarly, the variable impedance unit 590 includes M impedance elements R41˜R4M and M switches SW41˜SW4M, wherein the switches and the impedance elements are respectively connected in parallel (for example, the switch SW41 and the impedance element R41 are connected in parallel), and these connected switches and impedance elements are further connected in series between one and another terminal of the variable impedance unit 590.
However, in the variable impedance units 580 and 590, at least one of the switches is turned off in order to avoid short circuit.
It should be mentioned that in the present embodiment, all the resistors in the gamma voltage generator 500 are used for generating impedances. In other words, the gamma voltage generator 500 in the present embodiment can be implemented with any elements which can produce impedance. Namely, the resistors used in the present embodiment can be replaced with long channel transistors or switching capacitors.
The voltage dividing elements 621˜622 respectively receive the interpolated gamma output voltages generated by the gamma voltage generators 611˜613 and divide these voltages to generate a plurality of divided interpolated gamma output voltages as the gamma voltages corresponding to a plurality of pixel data grayscales.
As described above, in the present invention, an interpolated gamma output voltage corresponding to a floating-point pixel data grayscale can be generated by using an operation amplifier through an interpolation technique. Thereby, image distortion can be avoided and the display quality of a display panel can be improved.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
Number | Date | Country | Kind |
---|---|---|---|
98105256 | Feb 2009 | TW | national |