JPH0414386A - Digital coding and decoding method for luminance signal - Google Patents

Abstract

PURPOSE:To simplify the coding of a video signal not including intermediate gradation without losing quality by adopting the method selecting only an information element required for reproduction when a video luminance signal with less intermediate gradation is recorded digitally. CONSTITUTION:An input NTSC signal is separated into a luminance signal Y and a chrominance signal at a Y/C separator circuit 1, the luminance signal Y is converted into a 4-bit digital signal by an A/D converter 2 and the result is inputted to a computer 3. The computer 3 applies compression conversion to the signal into 3-bit signal and stores the result to a storage device 4. The computer 3 reads 3-bit information from the storage device 4 and inverts the signal into a 4-bit signal and the result is outputted via a D/A converter 5.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for digitally encoding and decoding an input video luminance signal, and in particular to compressing and encoding the number of digits of a bit value that represents the digital value. This relates to a decoding method.

(Summary of the Invention) The present invention relates to a method for digitally encoding and decoding an input video luminance signal.
During digital encoding, the number of digits of the bit value that represents the digital value is compressed and converted, and during decoding, the portion compressed during encoding is transferred as is and decoded using the digital value. In this way, it is possible to propose a method for encoding and decoding even when using a small-scale converter and memory.

(Conventional technology) In conventional technology, in order to make quantization noise invisible,
Video luminance signals that do not include intermediate gradations are also digitally encoded and decoded within or outside of 8 bits, just like video luminance signals that include intermediate gradations.

(Problem to be solved by the invention) When applying personal computers to broadcasting sites, conventional digitization technology places too much load on the equipment, and a large number of calligraphy characters, such as those used in sumo broadcasting efforts, are used, and the database is It was difficult to link it to the computer from the viewpoint of storage capacity and processing speed.

Therefore, an object of the present invention is to provide a system that can be applied to the graphic screens of personal computers that are currently common.
It is an object of the present invention to provide a digital encoding and decoding method for a luminance signal that simplifies the encoding of a video luminance signal that does not include intermediate gradations without degrading the quality.

(Means for Solving the Problems) In order to achieve this object, the method for digitally encoding and decoding a luminance signal of the present invention converts an input video luminance signal from analog to digital via an A/D converter. /D converted digital value is compared with a predetermined luminance threshold value, and the A
/D-converted digital values that do not exceed the luminance threshold are set to zero, and the number of digits of the bit value that should represent the digital value is compressed and converted and encoded,
When decoding the encoded digital values, the encoded digital values corresponding to the digital values before compression conversion exceeding the luminance threshold correspond to the digital values before compression conversion exceeding the luminance threshold, respectively. The coded digital values corresponding to the digital values before compression conversion that do not exceed the brightness threshold are inversely converted to zero digital values, and these inversely converted digital values are It is characterized in that it is converted into an analog signal via a D/A converter.

(Function) According to the method of the present invention, when digitally recording a video luminance signal with few intermediate gradations in a television or the like, a method is adopted to select only the information elements necessary for reproduction, so that the recorded data Since it reduces the amount of information (data) to be broadcast, it becomes possible to reproduce bright and dark images of any design with high quality using equipment with small storage capacity (for example, a personal computer). ) and images of any design can be directly connected to a computer, expanding the scope of adaptive work.

-For example, sumo broadcasts traditionally display efforts using unique calligraphy characters (also called sumo characters).
In this case, by using the present invention, the effort display screen can be easily edited and sent on a personal computer based on the effort data.

As another example, when transmitting a relay program with a simple equipment configuration, it is also possible to use a small-scale personal computer to play back and supervise videos of any design on site.

(Example) Normally, when a video luminance signal is digitized, its gradation is 8.
It is expressed in bits. However, when handling white and black video signals that do not include intermediate gradations, the video luminance signal takes only two values, white and black, so intuitively it is thought that 1-bit representation is sufficient. If this intuition is correct,
When the sampling period is the same as 8 bits, the amount of data for monochrome representation can be reduced to one-eighth (8 bits vs. 1 bit) compared to 8 bits representation. However, when actually expressed using one bit, the reproducibility is poor, and what should be a smooth straight line ends up becoming a jagged straight line. This is a visual representation of so-called quantization noise. If we simply consider that in order to make this quantization noise invisible, it is necessary to increase the sampling period by about 8 times, then this would be the same amount of data as the 8-dot representation.

Is there really a way to reduce the amount of data? We will discuss the solution below.

For example, in Figure 2, the position of each point of the diagonal line ((a) in the same figure) (the position of the horizontal axis corresponding to the position of the vertical axis of each point of the diagonal line) is 1
The quantization noise (jaggies) that is visible when expressed in bits is shown in an enlarged view in FIG. 2(b).

In the enlarged view of FIG. 2(b), diagonal lines are expressed as perpendicular lines in both the upper and lower parts, but there is a one-dot difference between the upper and lower parts to represent the diagonal components. However, visually, it does not feel like a diagonal component, and only two perpendicular lines appear shifted.

However, if a correction element whose gradation level is gradually attenuated is placed parallel to this line as shown in FIG. 3, the two perpendicular lines will appear as one diagonal line. In FIG. 3, each gradation level is indicated by the number of hatches. In other words, the greater the number of hatched lines, the higher the density.

By the way, human vision perceives a dark place immediately adjacent to a bright place as black until the darkness reaches a certain level of brightness, and even after reaching a certain level of brightness, changes in brightness are not noticeable when viewed alone. I never feel sensitive.

By utilizing this visual characteristic, the correction element shown in FIG. 3 may be black below a certain level, and it is not necessary to accurately represent the gray scale of intermediate tones above a certain level. In other words, the gradation level necessary to express the correction element can be expressed using 3 bits (8 gradations) as shown in Figure 4, for example. .

Based on the above idea, this invention expresses a video luminance signal with relatively few intermediate gradations using 2 bits to several bits, thereby reducing the amount of data from one-fourth of that of the conventional method (8 bits vs. 2 bits) approximately one-third (8 bits vs. 3
bit).

FIG. 1 shows an outline of a specific, but not limited, circuit configuration diagram for implementing the method according to the present invention.

Input NTSC signal (analog signal) is Y/C separation circuit 1
The luminance signal Y and the chroma signal C are separated, and the method of the present invention deals with only the luminance signal Y of these signals. It is assumed that the luminance signal Y is converted by the A/D converter 2 into a digital signal with an information width of 4 bits, for example. At this time, it is assumed that the relationship between the input video signal brightness level and the 4-bit information is as shown in the first and second columns of Table 1.

Next, the bit information is reduced, the 4 bits of input information is compressed into 3 bits, and the information is stored in the storage device 4.
Convert it to a column.

In other words, the brightness threshold at this time is 8 (100
All digital values from 8 (1000) to O(0000) are set to O(000) in 3-bit information, and are set to 8 in 4-bit information.
Digital values exceeding 9 (1001) to 15 (111
1) is 3-bit information 1 (001) to 7 (111
).

This conversion is performed by the computer 3, and the 3-bit information is stored in the storage device 4. This is the encoding process of the present invention.

The decoding process then begins by reading out the 3-bit information stored in the storage device 4. The 3-bit information is then reversely converted into 4-bit information, and at this time the following steps are performed. In other words, the digital values 1 (001) to 7 encoded into 3 bits correspond to the digital values 9 (1001) to 15 (1111) before compression conversion that exceed the predetermined brightness threshold 8 (1000) using 4-bit information. (111) is inversely transformed corresponding to digital values 9 (1001) to 15 (1111) before compression conversion that exceed the brightness threshold, and digital values 8 (1000) before compression conversion that do not exceed the brightness threshold 8. ) to 0 (0
000) corresponding to the encoded digital value 0(000
) is the digital value 0 (
0000). This operation is of course performed by the computer 3, and finally converted into an analog signal by the D/A converter 5 and output.

The above can be applied when drawing white calligraphy characters on a black background, and conversely, when drawing black calligraphy characters on a white background.

In addition, when using an 8-bit converter for A/D conversion,
For example, values from 0 to 127 are stored as zero, and values from 128 to 2 are stored as zero.
Divide the value of 55 into 7, correspond to 236 or more to 7, 218 or more to 6, 200 or more to 5, 182 or more to 4, 164 or more to 3, 146 or more to 2, 128 or more to 1. It is a good idea to memorize it.

Although one embodiment of the method of the present invention has been described in detail above, it is obvious to those skilled in the art that the present invention is not limited thereto, and that various modifications and changes can be made within the scope of the claims. Will.

Table 1 (Effects of the Invention) Until now, there has been no device that reproduces a video signal of any design that does not include intermediate gradations (especially super material) based on database processing.

The reason for this is that although such a device has limited uses, it requires a large-scale device and is not economical.

According to the present invention, it has become possible to develop a small-scale device that is suitable for the intended use, and it has also become sufficiently economical.

Because it is easy to incorporate this method into applications, especially on PCs, it is expected to be used in situations that were previously out of reach.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an overview of the circuit configuration for implementing the method according to the present invention, Fig. 2 is a diagram schematically showing an image obtained when the diagonally lined position is binarized, and Fig. 3 is a correction Figure 4 shows an image in which the diagonal lines shown in the second figure are reproduced by adding . ■...Y/C separation circuit 2...A/D converter 3
...Computer 4...Storage device 5...D
/A converter

Claims (1)

[Claims] 1. A/D converting the input video luminance signal via an A/D converter, comparing the A/D converted digital value with a predetermined luminance threshold, Digital values whose D-converted digital values do not exceed the luminance threshold are set to zero, and the number of digits of the bit value that should represent the digital value is compressed and converted and encoded, and the encoded digital values are In decoding the values, the encoded digital values corresponding to the digital values before compression conversion exceeding the luminance threshold are inversely transformed corresponding to the digital values before compression conversion exceeding the luminance threshold, and The encoded digital values corresponding to the digital values before compression conversion that do not exceed the luminance threshold are inversely converted to zero digital values, and these inversely converted digital values are sent to a D/A converter. A method for digitally encoding and decoding a luminance signal, the method comprising: converting the luminance signal into an analog signal through the digital encoding and decoding method. 2. The method according to claim 1, wherein the encoded digital value is once recorded in a storage device, and upon decoding, the recorded digital value is reproduced from the storage device. A method for digitally encoding and decoding signals. 3. A method for digitally encoding and decoding a luminance signal according to claim 1 or 2, wherein the luminance threshold value is approximately half the maximum value of the input luminance signal.