JPH05236401A - Video signal processing circuit of liquid crystal panel - Google Patents

Abstract

PURPOSE:To execute liquid crystal display with high gradation and contrast characteristics even when the dynamic range of input video signals is large. CONSTITUTION:A dynamic range detection circuit 7 calculates a dynamic range (p) of video signals. Based on the dynamic range (p), a DC offset voltage (q) is prepared by an offset amount setting, circuit 8 and supplied to a DC adder circuit 3. The DC adder circuit 3 adds the DC offset voltage (q) to a video signal (a), and a non-linear amplifier circuit 4 adjusts a level so as to compress the high luminance part of the video signal added the DC offset voltage (q) and outputs a video signal (b) of which dynamic range is adjusted to a fixed value A. Since only the high luminance part is compressed when the dynamic range of input video signals is large, the image has the high gradation and contrast characteristics so as not be painted out in black.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a liquid crystal panel (hereinafter referred to as L
The present invention relates to a video signal processing circuit of a CD panel).

[0002]

2. Description of the Related Art FIG. 3 is a block diagram illustrating a configuration of a conventional video signal processing circuit of an LCD panel. In FIG. 3, an A / D conversion circuit 21 converts a luminance signal (hereinafter referred to as Y signal) into, for example, an 8-bit parallel digital video signal, and a clamp circuit 22 sets the pedestal of the digital video signal to a predetermined level. It clamps and outputs the video signal a. The AGC circuit 23 uses the video signal a
Of the video signal b by adjusting the dynamic range of the video signal b to a dynamic range according to the input voltage of the LCD panel 29 versus the display luminance characteristic, and the clamp circuit 24 outputs the video signal b
The pedestal of is clamped to a predetermined level, and the D / A conversion circuit 25 converts the video signal c output by the clamp circuit 24 into an analog video signal (output Y signal).

The above is the video signal processing circuit. The decoder 26 outputs the output Y signal and the separately input RY signal and B signal.
-Create R, G, and B signals from Y signal and X driver 2
7 supplies R, G, B signals to the LCD panel 29. In addition, the Y driver 28 uses the LCD panel 2 to generate a timing signal generated based on a synchronization signal (not shown) of the video signal.
Supply to 9. With the above configuration, color display by the R, G, B signals is performed on the LCD panel 29.

FIG. 4 is an input / output level characteristic diagram of the video signal processing circuit. Hereinafter, the input / output level conversion of the conventional video signal processing circuit of the LCD panel will be described with reference to FIGS. 3 and 4. Since the LCD panel 29 has a narrow dynamic range of input voltage for displaying gradation accurately, it is desirable to adjust the dynamic range of the input R, G, B signals within that range.

Therefore, conventionally, as shown in FIG. 4, the dynamic range of the video signal a input to the AGC circuit 23 (the level difference between the white peak and the pedestal p1 to p3).
The gains g1 to g3 of the AGC circuit 23 are increased or decreased according to
After adjusting the output video dynamic range of the AGC circuit 23 to a constant value A to obtain the video signal b, the clamp circuit 2
4, the pedestal of the video signal b was clamped to a predetermined level.

[0006]

However, in the conventional video signal processing circuit of the LCD panel, the gain of the AGC circuit is increased / decreased according to the dynamic range of the input video signal, so that both dark and bright images are evenly distributed. Since the video signal level is low, there is a problem that the screen has no gradation and no contrast.

An object of the present invention is to solve the above problems and provide a video signal processing circuit of an LCD panel capable of obtaining an image having good gradation characteristics and contrast characteristics.

[0008]

In order to solve the above problems, the present invention provides a video signal processing circuit for an LCD panel, which detects the dynamic range of an input video signal and the output of this circuit. A circuit for adding a DC offset voltage to the input video signal and compressing the level of the high-luminance portion is provided to convert the input video signal into an output video signal having a constant dynamic range.

[0009]

According to the present invention, since the video signal processing circuit of the LCD panel is configured as described above, the DC offset voltage according to the dynamic range of the input video signal is added to the input video signal, and the input video signal The high brightness portion is compressed according to the dynamic range, and a video signal having a constant dynamic range is output. Therefore, when this video signal is applied to the LCD panel, an image with good gradation characteristics and contrast characteristics without blackout is displayed on the LCD panel.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 is a block diagram showing a configuration of a video signal processing circuit according to an embodiment of the present invention, and FIG. 2 is an input / output level characteristic diagram thereof. A / D conversion circuit 1 receives input Y
The signal is converted into, for example, an 8-bit parallel digital video signal, and the clamp circuit 2 clamps the pedestal of the digital video signal output from the A / D conversion circuit 1 to a predetermined level to add the video signal a to the DC addition circuit 3 Output to.

The dynamic range detection circuit 7 detects the white peak and pedestal level of the digital video signal output from the A / D conversion circuit 1 and calculates the dynamic range p. The offset amount setting circuit 8 creates a DC offset voltage q based on the input / output level characteristics shown in FIG. 2 based on the dynamic range p calculated by the dynamic range detection circuit 7, and the DC addition circuit 3 and the clamp voltage creation circuit 9 Output to.

The DC adder circuit 3 adds the DC offset voltage q to the video signal a and outputs it to the nonlinear amplifier circuit 4.
The nonlinear amplifier circuit 4 adjusts the level of the video signal output by the DC adder circuit 3 based on the input / output level characteristic shown in FIG. 2, and outputs the video signal b whose dynamic range is adjusted to a constant value A. The clamp circuit 5 clamps the pedestal of the video signal b to a predetermined level by using the clamp voltage generated by the clamp voltage generation circuit 9 according to the DC offset voltage q, and outputs the video signal c.

The D / A conversion circuit 6 converts the video signal c output by the clamp circuit 5 into an analog video signal. Since the subsequent processing is the same as that of the conventional example shown in FIG. 3, description thereof will be omitted. Next, the input / output level conversion operation of the video signal processing circuit of the LCD panel according to the embodiment of the present invention will be described with reference to FIGS.

First, as shown in FIG. 2, the gain of the nonlinear amplifier circuit 4 is configured so that the input voltage is G1 up to p1 and becomes G2 (G1> G2) when it exceeds p1. Further, the DC offset voltage q is set to 0 until the dynamic range of the input video signal is p1, and becomes larger as the dynamic range increases when it exceeds p1. Then, the dynamic range of the output video signal of the nonlinear amplifier circuit 4 is set to a constant value A.

Therefore, when the dynamic range p calculated by the dynamic range detection circuit 7 is p1, the direct current offset voltage q added by the direct current addition circuit 3 is 0, and from the low luminance portion to the high luminance portion of the input video signal,
It is amplified with a constant gain G1. Then, the dynamic range of the output video signal b of the nonlinear amplifier circuit 4 becomes A1.

Further, the dynamic range p is p2 (p2
> P1), the DC offset voltage added by the DC adder circuit 3 is q2, and in the video signal to which the DC offset voltage q2 is added, the portion up to the level p1 is the gain G.
The signal is amplified by 1 and the portion exceeding the level p1 is amplified by the gain G2. That is, the level of the high brightness part is compressed with respect to the low brightness part. Then, the dynamic range of the output video signal b of the nonlinear amplifier circuit 4 becomes A2.

Similarly, the dynamic range p is p3 (p
3> p2), the DC offset voltage added by the DC adder circuit 3 is q3 (q3> q2), and in the video signal added with the DC offset voltage q3, the portion up to the level p1 is amplified by the gain G1. , The portion exceeding the level p1 is amplified by the gain G2. That is, the level of the high brightness portion is further compressed. And the nonlinear amplifier circuit 4
The output video signal b has a dynamic range of A3.

Here, A1, A2, and A3 differ only in the DC level, and the AC amplitude is constant at the constant value A. Therefore, the pedestal of the video signal b is fixed by the clamp circuit 5 at a voltage corresponding to the DC offset voltage q. When clamped to the level, a video signal c having a constant pedestal level and a constant dynamic range can be obtained. As described above, in this embodiment, the higher the dynamic range of the input video signal, the more the high-luminance portion is compressed. Then, the dynamic range of the output video signal is held at a constant value A. When only the gain of the signal processing system is increased or decreased as in the conventional example, if the dynamic range of the input video signal is large, the bright portion and the dark portion are compressed at the same ratio. On the other hand, in the case of the present embodiment, the high-luminance portion can be suppressed, but the low-luminance portion is the same as when the dynamic range of the input video signal is p1, and therefore there is little blackout.

The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention, which are not excluded from the scope of the present invention. For example, the gain of the non-linear amplification circuit may be changed in multiple stages according to the characteristics of the LCD panel. Further, the clamp circuit 2, the DC addition circuit 3, the non-linear amplification circuit 4, the clamp circuit 5 and the offset amount setting circuit 8 of FIG.
May be configured by a ROM table (look-up table). Further, the present invention can be applied to a monochrome video signal. Further, the present invention can be configured with an analog circuit.

[0020]

As described above in detail, according to the present invention, a DC offset voltage corresponding to the dynamic range of an input video signal is added, and a high luminance portion is compressed to obtain a constant dynamic range. Since the video signal is converted into the existing video signal, the high-luminance portion can be suppressed while the gradation of the low-luminance portion remains unchanged.

Therefore, an image with less blackout and whiteout is displayed. Further, even if the brightness of the input video signal changes, it is not necessary to adjust the brightness each time so that it is easy to see.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a video signal processing circuit according to an embodiment of the present invention.

FIG. 2 is an input / output level characteristic diagram of the video signal processing circuit according to the embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a video signal processing circuit of a conventional LCD panel.

FIG. 4 is an input / output level characteristic diagram of a conventional video signal processing circuit.

[Explanation of symbols]

 1,6 A / D conversion circuit 2,5 Clamp circuit 3 DC addition circuit 4 Non-linear amplification circuit 7 Dynamic range detection circuit 8 Offset amount setting circuit 9 Clamp voltage creation circuit

Claims (1)

[Claims] 1. A circuit for detecting a dynamic range of an input video signal; (b) adding a DC offset voltage to the input video signal according to an output of the circuit; A video signal processing circuit for a liquid crystal panel, comprising a compression circuit and converting an input video signal into an output video signal having a constant dynamic range.