JP2832078B2 - How to adjust black level of image signal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for adjusting a black level of an image signal.

2. Description of the Related Art As an image signal processing apparatus for converting an analog image signal into a digital signal and processing it, there is, for example, one having a configuration as shown in FIG.

In FIG. 2, 1 is a clamp circuit, 2 is an A / D converter, 3 is a digital signal processing circuit, 4 is a D / A converter, 5
Is a variable voltage source, and its operation will be described below.

In FIG. 1, an analog image signal input from an input terminal a is supplied to a variable voltage source 5 in a clamp circuit 1 at the timing of a clamp pulse input from an input terminal b.
Is set in advance and clamped to the supplied clamp level.

The analog image signal clamped by the clamp circuit 1 is converted into digital data by an A / D converter 2 in synchronization with a clock pulse input from an input terminal c, and then input to a digital signal processing circuit 3. You.

The digital signal processing circuit 3 is supplied with a clock pulse input from an input terminal d in addition to a clock pulse input from an input terminal c. The digital signal processing circuit 3 supplies the digital signal supplied from the A / D converter 2 to the digital signal processing circuit 3. The data is converted to data indicating “0” during a blanking period specified by a blank pulse, or subjected to various other digital signal processing, and then supplied to the D / A converter 4.

The digital data processed by the digital signal processing circuit 3 is converted into an analog image signal in synchronization with a clock pulse input from an input terminal c, and then output from an output terminal e.

[Problems to be Solved by the Invention] However, as described above, in the image signal processing circuit shown in FIG. 2, the blanking level is adjusted by adjusting the set voltage level of the variable voltage source 5 and changing the clamp level. So that the black level of the input image signal is made lower than the blanking level by the setting of the clamp level. Since the output digital data does not become "0" or less, it is difficult to perform the black level adjustment.

Further, even when the minimum reference potential of the A / D converter 2 is adjusted in accordance with the level of the image signal input to the A / D converter 2, an error easily occurs and the configuration becomes complicated. Adjustment becomes difficult.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for adjusting the black level of an image signal, which can accurately and easily adjust the black level of the image signal.

[Means for Solving the Problem] According to the black level adjustment method for an image signal of the present invention, an analog image signal is input, the input analog image signal is clamped to a predetermined level, and the clamped analog image signal is converted to a digital signal. In the image signal processing for converting to an image signal, a method of adjusting a black level of the analog image signal, wherein the black level is adjusted during a blanking period of a digital image signal formed from an input analog image signal. The black level of the analog image signal is adjusted by offsetting the level to a first level and adjusting the clamp level in the clamping process using the digital image signal whose level in the blanking period is offset by the first level. After adjusting the analog image signal from the input analog image signal by the image signal processing A level conversion process for converting a level of a blanking period of a digital image signal to be formed into a second level different from the first level is performed, and the digital image signal subjected to the level conversion process is subjected to the image signal processing. Is output as a digital image signal formed by.

[Operation] According to the above-described method, the black level of the image signal can be accurately adjusted.

[Examples] Hereinafter, the present invention will be described using examples of the present invention.

FIG. 1 is a diagram showing a schematic configuration of an image signal processing apparatus as one embodiment of the present invention. In FIG. 1, the same components as those of the apparatus shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, an analog image signal input from an input terminal a is clamped by a clamp circuit 1 in the same manner as the configuration shown in FIG. 2, and then converted into digital data by an A / D converter 2. It is supplied to the A terminal of the switching switch 6.

Further, the switching switch 6 is supplied with, for example, offset data representing a predetermined voltage level (for example, digital data representing a voltage level "15") from the input terminal f to the B terminal, and switches according to a blank pulse inputted from the input terminal d. The operation is controlled, and the switching switch 6 is connected to the A terminal side except during the blanking period.
Digital data output from the A / D converter 2 is output, and is connected to the B terminal during a blanking period.
Offset data is output.

As described above, the switching switch 6 outputs digital data in which the voltage level during the blanking period is offset, and the blanking level (in this case, “1”) is output.
Digital data of a level lower than the digital data representing 5 ") is also output.

The digital data output from the switching switch 6 is supplied to the A terminal of the switching switch 8 and the ten terminal of the digital subtractor 7.

The offset data input to the input terminal f is supplied to one terminal of the digital subtracter 7, and the digital subtracter 7 sets the offset data from the digital data output from the switching switch 6. The digital data from which the data has been subtracted is output and supplied to the B terminal of the switching switch 8.

The switching switch 8 is normally connected to the terminal B in the figure, and the level of the blanking period is offset by the switching switch 6, and the level of the blanking period that is offset by the digital subtracter 7 is "0".
The digital data obtained is converted into a digital signal processing circuit 9
The digital signal processing circuit 9 subjects the digital signal processing circuit 9 to various digital signal processing, converts the analog signal to an analog image signal in the D / A converter 4, and outputs the analog image signal from an output terminal e.

The switching switch 8 is connected to the A terminal side in the figure by a control signal supplied from a system controller (not shown) via an input terminal g when the black level of the input image signal is adjusted. The digital data whose level has been offset is converted into an analog signal by the D / A converter 4 after passing through the digital signal processing circuit 9 and is output. Therefore, when the black level is adjusted, the digital signal exceeds the blanking level (ie, "15"). It can monitor low-level digital data and make accurate and easy adjustments.

In the present embodiment, the case where the data offset of the blanking level is set to "15" has been described. However, the present invention is not limited to this, and data of any level may be used as offset data.

Further, the clamp circuit used in the present embodiment clamps at the timing of a clamp pulse, but may be a clamp circuit that detects and clamps a minimum potential such as a sync tip level of an input image signal.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a method for adjusting the black level of an image signal, which can accurately and easily adjust the black level of the image signal. Become.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an image signal processing apparatus as one embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration of a conventional image signal processing device. DESCRIPTION OF SYMBOLS 1 ... Clamp circuit 2 ... A / D converter 4 ... D / A converter 5 ... Variable voltage source 6, 8 ... Switching switch 9 ... Digital signal processing circuit

Claims (1)

(57) [Claims] An image signal processing for inputting an analog image signal, clamping the input analog image signal to a predetermined level, and converting the clamped analog image signal into a digital image signal. A method of adjusting a level, wherein at the time of adjusting a black level, a level of a blanking period of a digital image signal formed from an input analog image signal is offset to a first level, and a level of the blanking period is adjusted. The black level of the analog image signal is adjusted by adjusting the clamp level in the clamp process using the digital image signal offset at the first level, and then the image signal is converted from the input analog image signal. Level of blanking period of digital image signal formed by processing Is converted to a second level different from the first level, and the digital image signal subjected to the level conversion is output as a digital image signal formed by the image signal processing. A method for adjusting a black level of an image signal.