JPH06350938A - Level controller for video signal - Google Patents

Abstract

PURPOSE:To allow the controller to extend a video signal in a black level direction and a white level direction and to provide an output of a video signal from which printed picture with modulation is obtained. CONSTITUTION:A clamp circuit 1 applies clamp processing to a pedestal portion of a luminance signal of a video signal and a bottom hold circuit 3 holds a bottom portion of the luminance signal whose pedestal portion is clamped to form a bottom hold signal. Then a limiter circuit 4 receiving a black reference level applies limiter processing to the bottom hold signal based on the black reference level and a blanking replacement circuit 5 replaces the blanking portion of the luminance signal subject to clamp processing with a level of the bottom hold signal subject to limiter processing. Then a gain variable amplifier 6 amplifies the luminance signal whose blanking portion is replaced up to a prescribed level to provide an output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal level control device suitable for use in, for example, a video printer device.

[0002]

2. Description of the Related Art Conventionally, a video printer device for printing an image or the like according to a video signal has been known.

In this video printer, when a video signal is supplied, first, the Y / C separation circuit separates the video signal into a luminance signal and a chroma signal, and an automatic gain control (AGC) circuit only the luminance signal. Supply to.

In the AGC circuit, as shown in FIG. 5A, the pedestal portion (black level) of the luminance signal (VS) is set.
Is clamped, the brightness signal is amplified until the peak level (white level) of the brightness signal reaches a target level as shown in FIG.

The chroma signal is supplied to the decoder in addition to the luminance signal. The decoder forms RGB primary color signals from the luminance signal and the chroma signal, and supplies the signals to the A / D converter.

The A / D converter forms three primary color data by digitizing the three primary color signals and supplies the data to the memory.

The three primary color data supplied to the memory is temporarily written in the memory under the write control of the control circuit. Then, by the read control of the control circuit, the data is read from the memory and supplied to the printer block.

The printer block drives the printer head based on the three primary color data.

As a result, an image corresponding to the three primary color data is printed by the printer head.

[0010]

However, in the AGC circuit provided in the video printer device, only the peak level (white level) of the luminance signal becomes a constant value (target level). Because the amplification is performed, if the supplied video signal is a low-contrast video signal and the black level is higher than the normal level (black floating), the printed image has no shading (no sharpness). There was a problem that became.

The present invention has been made in view of the above-mentioned problems, and it is possible to output a video signal capable of printing a sharp image by correcting the black floating of the video signal. It is an object of the present invention to provide a level control device for various video signals.

[0012]

A video signal level control device according to the present invention detects a level of a pedestal clamp means for clamping a pedestal portion of a video signal and a bottom portion of the video signal from the pedestal clamp means. A bottom level detection means for outputting a bottom level detection signal, and a pedestal conversion means for outputting the level of the bottom level detection signal from the bottom level detection means as the level of the pedestal portion of the video signal from the pedestal clamp means. The above-mentioned problem is solved by having amplification means for amplifying and outputting the video signal from the pedestal conversion means so as to have a predetermined level.

The video signal level control device according to the present invention compares the level of the bottom level detection signal from the bottom level detection means with a reference black level,
The above problem is solved by having a limiter means for supplying a bottom level detection signal whose level is controlled to the reference black level to the pedestal conversion means.

[0014]

The video signal level control apparatus according to the present invention controls the level of the bottom portion of the video signal from the pedestal clamp means for clamping the pedestal portion of the video signal.
Detected by the bottom level detection means, the pedestal conversion means, by setting the level of the bottom level detection signal from the bottom level detection means to the level of the pedestal part of the video signal from the pedestal clamp means, Stretches toward black level. Then, the amplifying means amplifies the video signal from the pedestal converting means to a predetermined level, thereby extending the video signal in the white level direction.

In the video signal level control device according to the present invention, the limiter means compares the level of the bottom level detection signal from the bottom level detection means with a reference black level, which serves as the reference. The bottom level detection signal level-controlled to the black level is supplied to the pedestal conversion means to stabilize the black level of the video signal.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a video signal level control device according to the present invention will be described below with reference to the drawings.

The video signal level control apparatus according to the present embodiment has a configuration as shown in FIG. 1, and the clamp circuit (pedestal clamp means) 1 clamps the pedestal portion of the luminance signal of the video signal. A bottom hold circuit (bottom level detection means) 3 holds the bottom portion of the luminance signal whose pedestal portion is clamped to form a bottom hold signal, and a limiter circuit (limiter means) 4 to which a black reference level is supplied, The bottom hold signal is limited based on the black reference level, and the blanking replacement circuit (pedestal conversion means) 5
The blanking part of the clamped luminance signal is
The level is changed to the level of the bottom hold signal subjected to the limiter process. Then, in the variable gain amplifier (amplifying means) 6,
The luminance signal that has replaced the blanking part above,
It is characterized in that it is amplified so as to have a predetermined level and then output.

The video signal level control device according to this embodiment having such a configuration can be used as the AGC circuit 22 of the video printer device having the configuration as shown in FIG. 2, for example.

That is, in FIG. 2, the video signal corresponding to the printed image is supplied to the video printer device through the input terminal 20. This video signal is supplied to the luminance / chroma separation circuit (Y / C separation circuit) 21. The Y / C separation circuit 21 separates the video signal into a luminance signal and a chroma signal, supplies the luminance signal as shown in FIG. 3A to the AGC circuit 22, and supplies the chroma signal to the decoder 23.

The luminance signal supplied to the AGC circuit 22 is supplied to the clamp circuit 1 via the input terminal 12 shown in FIG.

The clamp circuit 1 clamps the pedestal portion of the luminance signal and supplies the luminance signal with the pedestal portion clamped to the gate circuit 2 and the blanking replacement circuit 5.

A window pulse as shown in FIG. 3B is supplied to the gate circuit 2 through the input terminal 13. This window pulse is a pulse for extracting the video signal of the printing area from the video signals of the signal effective area in image printing, as shown by the diagonal lines in FIG. The gate circuit 2 outputs the video signal from the clamp circuit 1 only while the low-level window pulse is supplied as shown in FIG. 3B. As a result, as shown in FIG. 3C, the video signal of the printing area is extracted and supplied to the bottom hold circuit 3.

The bottom hold circuit 3 is the same as that shown in FIG.
As shown in (c), the level of the bottom portion of the video signal (the portion having the lowest level of the luminance signal) is held, and this bottom hold signal is supplied to the limiter circuit 4.

A black reference level signal indicating a reference level of a black level as shown by a dotted line in FIG. 3D is supplied to the limiter circuit 4 through the input terminal 14. The limiter circuit 4 compares the level of the black reference level signal with the level of the bottom hold signal, and if the level of the bottom hold signal is less than or equal to the level of the black reference level signal, then outputs the bottom hold signal. It is supplied to the blanking replacement circuit 5 as it is. When the level of the bottom hold signal is equal to or higher than the level of the black reference level signal, the level of the bottom hold signal is set to the level of the black reference level signal, and this is supplied to the blanking replacement circuit 5.

A blanking signal indicating, for example, a horizontal blanking period is supplied to the blanking replacement circuit 5 via an input terminal 15. When the blanking signal is supplied to the blanking substitution circuit 5, the level of the blanking portion of the luminance signal supplied from the clamp circuit 1 is changed from the limiter circuit 4 as shown in FIG. The level of the supplied bottom hold signal (the level of the black reference signal when the black reference level signal is supplied from the limiter circuit 4) is replaced and output.

As a result, even if the brightness signal of the video signal relating to the image to be printed has a "black floating" such that the brightness level of the contrast is low and the black level is higher than the normal level, The luminance signal can be expanded in the black level direction, and the "black floating" can be corrected and output.

Further, since the limiter circuit 4 compares the bottom hold signal with the black reference signal for limiter processing, even if a luminance signal having a high level is supplied as a whole, the image pickup signal is obtained. The level of the pedestal part can be suppressed to the level of the black reference signal. Therefore, it is possible to output a stable luminance signal of the black level.

The luminance signal subjected to such blanking replacement processing is supplied to the variable gain amplifier 6.

The variable gain amplifier 6 has its gain varied by a gain control signal described below, amplifies the luminance signal by the varied gain, and outputs it through the output terminal 16.

That is, the brightness signal from the variable gain amplifier 6 is output through the output terminal 16 and is also supplied to the average value detection circuit 7 and the peak detection circuit 8.

The average value detection circuit 7 detects the average level of the luminance signal and supplies it to the adder 10.

The peak detection circuit 8 detects the peak level of the luminance signal and supplies it to the adder 10.

The adder 10 includes the average value detection circuit 7
Is added to the peak level from the peak detection circuit 8 and the added signal is supplied to the comparison signal input terminal of the comparator 11.

At the reference signal input terminal of the comparator 11,
The reference level is supplied from the reference level output circuit 9. The comparator 11 compares the reference level with the level of the addition signal and supplies the comparison output to the variable gain amplifier 6 as the gain control signal.

The variable gain amplifier 6 is adapted to be varied to a predetermined gain in accordance with the level of the gain control signal, and by amplifying the luminance signal with the variable gain, As shown in 3 (f), the peak level of the luminance signal is raised to a predetermined level and output.

As a result, not only the above-described expansion processing in the black level direction but also the expansion processing in the white level direction is performed on the luminance signal, so that the level of the luminance signal can be increased.

The luminance signal from the variable gain amplifier 6 is
It is supplied to the decoder 23 shown in FIG. 2 via the output terminal 16.

As described above, the chroma signal is supplied to the decoder 23 in addition to the luminance signal. The decoder 23 forms a video signal of three primary colors (RGB) on the basis of the luminance signal and the chroma signal, and the video signal is A /
It is supplied to the D converter 24.

The A / D converter 24 forms video data by digitizing the video signal and supplies it to the memory 25.

The video data supplied to the memory 25 is once stored and read in the memory 25, and the D / A
The converted video signal is supplied to the external connection terminal 29 to which a monitor device or the like is connected, and also to the printer block 27 as a video signal.

The printer block 27 drives the printer head 28 according to the video data.

As a result, an image corresponding to the video data is printed by the printer head 28.

As described above, the printer block 27
The video data supplied to is corrected for the above-mentioned "black floating" and further level-expanded in the black level direction and the white level direction. Therefore, even when a low-contrast video signal is supplied through the input terminal 20, it is possible to obtain a good printed image with sharpness.

Further, since the video data is subjected to the limiter processing by the limiter circuit 4 so as not to reach a predetermined level or higher, it is possible to obtain a printed image with stable contrast.

In the description of the above embodiment, the blanking replacement circuit 5 sets the level of the blanking portion of the luminance signal from the clamp circuit 1 to the level of the bottom hold signal from the limiter circuit 4. Instead of this, the level of the pedestal portion of the luminance signal may be lowered according to the level of the bottom hold signal. Further, it may be lowered according to the level of the horizontal synchronizing signal of the luminance signal. Even with this modification, the same effect as that of the above-described embodiment can be obtained.

[0046]

As is apparent from the above description, in the video signal level control device according to the present invention, the level of the bottom portion of the video signal from the pedestal clamp means for clamping the pedestal portion of the video signal is set to the bottom level. Detected by the detection means, the pedestal conversion means sets the level of the bottom level detection signal from the bottom level detection means to the level of the pedestal portion of the video signal from the pedestal clamp means, thereby making the video signal a black level. In the same way, the amplification means amplifies the video signal from the pedestal conversion means to a predetermined level, thereby expanding the video signal in the white level direction.

As a result, even if black floating occurs in the video signal, it is possible to form and output a video signal corrected for this. Therefore, when the level control device for the video signal is applied to the video printer, printing can be performed by the video signal in which the above-mentioned black floating is corrected, and therefore, even when a low-contrast video signal is supplied, It is possible to obtain a good printed image with a high quality.

Further, in the video signal level control device according to the present invention, the limiter means compares the level of the bottom level detection signal from the bottom level detection means with a reference black level, which serves as the reference. By supplying the pedestal conversion means with the bottom level detection signal whose level is controlled to the black level, the black level of the video signal can be stabilized. Therefore, when the video signal level control device is applied to a video printer device, even if a low-contrast video signal is supplied, it is possible to obtain a good printed image with a sharp contrast and a stable contrast. Can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of a video signal level control apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a block diagram when the video signal level control device according to the embodiment is applied to a video printer device.

FIG. 3 is a waveform diagram for explaining the operation of each unit of the video signal level control device according to the embodiment.

FIG. 4 is a schematic diagram for explaining a print area of a video signal extracted by a window pulse used in the video signal level control device according to the embodiment.

FIG. 5 is a waveform diagram of a video signal for explaining the amplification processing of only the white level of the video signal in the conventional video printer device.

[Explanation of symbols]

1 ・ ・ ・ ・ ・ ・ ・ ・ Clamp circuit 2 ・ ・ ・ ・ ・ ・ ・ ・ Gate circuit 3 ・ ・ ・ ・ ・ ・ ・ ・ Bottom hold circuit 4・ ・ ・ ・ ・ ・ ・ ・ Limiter circuit 5 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Blanking replacement circuit 6 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Variable gain amplifier 7 ・ ・ ・ ・ ・ ・ ・ ・ Average detection circuit 8 ・ ・ ・ ・ ・ ・ ・ ・ Peak detection circuit 9 ・ ・ ・ ・ ・ ・ ・ ・ Reference Level output circuit ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Adder 11 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Comparator 12 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Luminance signal input Terminal 13 ・ ・ ・ ・ ・ ・ Window pulse input terminal 14 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Black reference level signal input terminal 15 ・ ・ ・ ・ ・ ・..Of blanking signals Input terminal 16 ... Output terminal 20 Input terminal 21 for video signal Brightness / Chroma (Y / C)
Separation circuit 22 ... Automatic gain control (AGC)
Circuit 23 ... Decoder 24 ... A / D converter 25 ... Memory 26 ...・ ・ ・ ・ ・ ・ ・ ・ D / A converter 27 ・ ・ ・ ・ ・ ・ ・ ・ ・ Printer block 28 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Printer head 29 ・ ・ ・ ・・ ・ ・ ・ ・ ・ ・ ・ External output terminal

Claims (2)

[Claims] 1. A pedestal clamp means for clamping a pedestal portion of a video signal, a bottom level detection means for detecting a level of a bottom portion of the video signal from the pedestal clamp means, and outputting a bottom level detection signal. The pedestal conversion means for outputting the level of the bottom level detection signal from the bottom level detection means as the level of the pedestal portion of the video signal from the pedestal clamp means, and the video signal from the pedestal conversion means to a predetermined level. A video signal level control device, comprising: 2. The bottom level detection signal from the bottom level detection means is compared with a reference black level, and the bottom level detection signal level-controlled to the reference black level is supplied to the pedestal conversion means. 2. The video signal level control apparatus according to claim 1, further comprising a limiter means for supplying the video signal.