JPH06113170A - A/d conversion method for television signal and its device - Google Patents

Abstract

PURPOSE:To prevent quantizing noise from becoming conspicuous even if an A/D conversion element whose number of bits is small is used by adding lower bits corresponding to the change amount of a clamping level to a digitized television signal. CONSTITUTION:A clamping circuit 1 clamps the reference voltage part of the inputted television signal based on reference voltage from a reference voltage generation circuit 5. At that time, a voltage shift circuit 6 shifts reference voltage, namely, a clamping level for respective fields in accordance with an order signal from a shift order generation circuit at every field 4. Then, lower two bits corresponding to the shift amount of the clamping level by an additional circuit 7 is added as the data to the television signal digitized by the A/D conversion circuit 2. Thus, the data which is lost by the shift of the clamping level is added, and the gradation of A/D conversion can be increased by visual averaging.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television signal A.
The present invention relates to a D / D conversion method and device.

[0002]

2. Description of the Related Art Conventionally, a high-speed A / D conversion element is required for A / D conversion of a television signal, but it is difficult to manufacture a high-speed and multi-gradation A / D conversion element. An 8-bit (256 gradation) A / D conversion element is widely used.

[0003]

However, when the 8-bit A / D conversion element is used as in the prior art, the quantization noise appears as a contour line on the screen in a smoothly changing scene. There is a drawback that

The present invention has been made in view of such a situation, and a television signal in which quantization noise is not noticeable even when an A / D conversion element having a small number of bits such as 8 bits is used. A first object of the present invention is to provide a method and apparatus for A / D conversion for use.

A second object of the present invention is to provide an A / D converter for television signals in which flicker is not a concern.

[0006]

The television signal A / D conversion method of the present invention changes the clamp level of the television signal for each field, digitizes the television signal clamped at the clamp level, and clamps. It is characterized in that lower bits corresponding to the amount of change in level are added to the digitized television signal.

The television signal A / D converter according to the present invention includes a clamp level changing means (for example, the voltage shift circuit 6 of the embodiment) for changing the clamp level of the television signal for each field, and a clamp at the clamp level. A / D conversion means (for example, 8-bit A / D conversion circuit 2 of the embodiment) for digitizing the converted television signal
And the lower bit corresponding to the amount of change in the clamp level,
It is characterized by comprising a lower bit addition means (for example, the lower 2 bit addition circuit 7 of the embodiment) for adding to the digitized television signal.

The television signal A / D converter according to the present invention preferably comprises a sequence control means (for example, the field-by-field shift sequence generation circuit 4 of the embodiment) for controlling the sequence in which the clamp level is changed.

[0009]

In the television signal A / D conversion method and apparatus of the present invention, the clamp level of the television signal is changed for each field, and the television signal clamped at the clamp level thus changed is used. The lower bits that are digitized and correspond to the amount of change in the clamp level are added to the digitized television signal. Therefore, by visual averaging, A /
The gradation of D conversion can be increased.

Further, when the order control means for controlling the order of changing the clamp levels is provided, the order of changing the clamp levels can be changed and flicker can be prevented.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an A / D for a television signal according to the present invention.
The structure of one Example of a converter is shown. In this embodiment, an 8-bit A / D conversion element is used to perform pseudo 10-bit A / D conversion. The clamp circuit 1 clamps the input television signal at a clamp level designated by a voltage shift circuit 6 described later. 8-bit A /
The D conversion circuit 2 digitizes the television signal clamped by the clamp circuit 1 into 8 bits and outputs the 8 bits.

The sync signal extraction circuit 3 extracts a field sync signal from the input television signal. The field-by-field shift order generation circuit 4 outputs a sequence signal indicating the order of the clamp level change according to the field synchronization signal extracted by the synchronization signal extraction circuit 3. The reference voltage generation circuit 5 produces a reference voltage which is a source of the clamp voltage. The voltage shift circuit 6 shifts the reference voltage output from the reference voltage generation circuit 5 according to the sequence signal from the sequence generation circuit 4, and specifies the clamp level for the clamp circuit 1. The lower 2 bit addition circuit 7 receives the sequence signal from the sequence generation circuit 4, and in synchronization with the voltage shift circuit 6, generates and adds the lower 2 bits corresponding to the voltage shift amount, that is, the clamp level change amount.

Next, the operation of the embodiment of FIG. 1 configured as described above will be described. The reference voltage portion (usually the black level) of the input television signal is the clamp circuit 1
According to the input D (dynamic) of the A / D conversion circuit 2.
The DC voltage is clamped based on the reference voltage output from the reference voltage generation circuit 5 so that the DC voltage has an appropriate value within the range. At this time, the voltage shift circuit 6 shifts (changes) the reference voltage, that is, the clamp level, for each field according to the order signal from the field shift order generation circuit 4.
Let Then, with respect to the television signal clamped by the shifted clamp level and digitized by the A / D conversion circuit 2, the lower 2 bits corresponding to the shift amount of the clamp level are added by the addition circuit 7 to the data. Is added as. As a result, the data lost due to the shift of the clamp level is added, and the original signal is restored at the output end.

FIG. 2 shows an example of values of sampling data, bits to be added, and output (restoration) patterns within a predetermined period when the clamp level for the input pattern is changed in the embodiment of FIG. In this example, the input pattern is a ramp waveform that increases monotonically from left to right in the screen. FIG. 2A shows a case where the clamp level shift amount is zero, and in this case, the added lower bit is 00B. FIG. 2B shows a case where the clamp level shift amount is -1/4 LSB. In this case,
The lower bit added is 01B. Figure 2 (c) shows
A case where the shift amount of the clamp level is −2/4 LSB is shown. In this case, the added lower bit is 10B. In FIG. 2D, the clamp level shift amount is −3 /
The case of 4 LSB is shown, and in this case, the added lower bit is 11B.

In the output pattern, that is, the restored data, the quantization threshold appears at different input levels according to the shift amount. As a result, the restored images for each field are visually averaged by superimposing the screens, so that an image corresponding to 10-bit gradation is obtained. When the clamp level is changed as shown in FIG. 2 and the lower bits according to the amount of change in the clamp level are added, as shown in FIG. 3, it is visually shown in FIG. 2 (a) (b) (c).
The output pattern of (d) is recognized as a superimposed pattern, and can be recognized as a smooth waveform.

As described above, when the clamp level is shifted for each field, a flicker phenomenon occurs due to a difference in reproduced waveform between the fields. In order to prevent this, the field-by-field shift order generation circuit 4 generates an order signal so as to change the clamp level shift order from, for example, the order of FIG. 4 to the order of FIG. Change the component ratio. As a result, the frequency component of flicker can be set in a region with low visual sensitivity, and an image without flicker can be reproduced.

[0017]

According to the A / D conversion method and apparatus for a television signal of the present invention, the clamp level of the television signal is changed for each field, and the television signal clamped at the clamp level thus changed. Is digitized, and the lower bits corresponding to the amount of change in the clamp level are added to the digitized television signal, so that the gradation of A / D conversion can be increased by visual averaging. , You can hide the quantization noise.

Further, since the order of changing the clamp levels can be changed by providing the order control means for controlling the order of changing the clamp levels, the frequency components of the flicker have low visual sensitivity. It becomes possible to make what was originally a minute level of flicker more visually unnoticeable.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an A / D conversion apparatus for television signals of the present invention.

FIG. 2 is a diagram showing an example of sampling data, a bit to be added, and an output (restoration) pattern within a predetermined period when the clamp level for an input pattern is changed in the embodiment of FIG.

FIG. 3 is a diagram showing an image obtained by superimposing the output patterns shown in FIG.

FIG. 4 is a diagram showing an example of a change order of clamp levels in the embodiment of FIG.

5 is a diagram showing another example of the changing order of the clamp levels in the embodiment of FIG.

[Explanation of symbols]

 1 clamp level 2 8-bit A / D conversion circuit 3 sync signal extraction circuit 4 field-by-field shift order generation circuit 5 reference voltage generation circuit 6 voltage shift circuit 7 lower bit addition circuit

Claims (4)

[Claims] 1. A clamp level of a television signal is changed for each field, the television signal clamped at the clamp level is digitized, and lower bits corresponding to the amount of change in the clamp level are
An A / D conversion method for a television signal, characterized by adding to the digitized television signal. 2. A clamp level changing means for changing the clamp level of the television signal for each field, an A / D converting means for digitizing the television signal clamped at the clamp level, and a change amount of the clamp level. The lower bit corresponding to
An A / D conversion apparatus for television signals, comprising: lower bit addition means for adding the digitized television signals. 3. The A / D conversion apparatus for television signals according to claim 2, further comprising an order control means for controlling an order in which the clamp level is changed. 4. The A / D conversion means converts into an 8-bit digital signal, and the lower bit addition means lower 2
The A / D conversion device for television signals according to claim 2 or 3, wherein a bit is added.