JPS6126275B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an orthogonal transform encoding method.

If we look at the power distribution of television signals statistically, there are few high frequency components. Focusing on this point, there is an idea of compressing the overall band by reducing the number of transmission bits used for high-frequency components and transmitting them. One example is a method using Hadamard transform as a means of converting the time domain to the frequency domain. For example, if an 8th-order Hadamard transform is performed, it can be expressed as the following equation.

Here, _[ x ₁ , _{x 2 ,} ...... ......h ₈ ] is an 8th order sequence transformed into the frequency domain by Hadamard transform. An example of compressing this sequence is shown in FIG. In this case, it will be possible to transmit at an average rate of 4.5 (pits/pixel). When linearly compressing a sequence h _i to 3 bits, conventionally the quantization step is set to 1 and the lower 3 bits b _i1 , b _i2 , b _i3
(See Figure 2a).

In some cases, the quantization step is set to 2 and three bits b _i2 , b _i3 , and b _i4 are transmitted (see FIG. 2b). In this method, although the transmission 3-bit area changes depending on the amount of quantization steps, it is fixed at the initial setting and does not correspond to changes in the input signal. However, although it is true that the power distribution of high-order sequences is small from a statistical perspective, in special images, the energy distribution may be stronger than expected. For such an image, even if the value of the sequence h _i becomes larger than the original 3 bits (for example, the lower 3 bits) and overflows the lower 3 bits, this value will eventually be transmitted in the lower 3 bits. Therefore, it has the disadvantage of causing distortion in the reproduced signal. That is, when the probability of overflow is small, it is not so noticeable on the screen, but when the probability of overflow increases, the deterioration of the screen becomes noticeable. In addition, the method previously proposed by the applicant (Japanese Unexamined Patent Publication No. 52-83014)
(No. Publication) switches the quantization step of the transmission sequence for the next fixed period based on the statistical value for a certain fixed period, but in this method, the quantization step is switched based on the statistical value for the previous fixed period. However, it cannot be said that the quantization step has been switched to the optimal quantization step, and there is room for improvement.

Therefore, an object of the present invention is to reproduce an image with less distortion by changing the amplitude range of each transmitted sequence by switching the bit position of each sequence to the optimum position according to the magnitude of the input signal. The object of the present invention is to provide an orthogonal transform encoding method that can perform the following steps.

In order to compensate for the drawbacks mentioned above, this invention detects the statistics of each sequence during a certain period, switches the quantization step for each sequence, and reduces the power of the h _i component. Even when the number of bits is increased, the number of bits remains the same, but by changing the quantization step, the area to be transmitted is expanded and transmitted, thereby transmitting an image with less distortion. For example, the lower 3 bits are normally transmitted as shown in FIG. 2a, and only when there is an overflow due to a special image, the 3 bits are transmitted as shown in FIG. 2b, c, d, e, and f.

The case where the fixed period for detecting statistics is one horizontal period will be described below based on the embodiment shown in FIG. The analog video signal supplied to the input terminal A is converted into a parallel 8-bit digital signal by the A/D conversion circuit 1. This signal is supplied to the Hadamard transform circuit 2, where it is orthogonally transformed to obtain the output of each sequence (h ₁ , h ₂ , . . . h ₈ ). Now, considering a block of sequence h _i , the output of sequence h _i will be an 8-bit signal if compression is not considered. This signal is
The data is led to a 1H memory (delay means) 3 and a statistics counter 4, which store data for one horizontal period, delay the data by the time width of one horizontal period, and output the data. The statistics counter 4 detects whether or not an overflow occurs in which bit of the upper 5 bits of h _i , that is, b _i8 , b _i7 , b _i6 , b _i5 , and b _i4 , in one horizontal period. are doing. Whether or not there is an overflow is determined based on whether the number of times each bit becomes "1" is equal to or greater than a certain number of times. For example, if the most significant bit position that has overflowed is b _i7 , the three transmission bits B _i3 , B _i
2 , B _i1 become b _i7 , b _i6 , b _i5 (see Figure 2 e). In this case, in order to indicate that b _i7 , b _i6 , and b _i5 are being transmitted, transmission mode instruction signals M _i1 , M _i2 , and M _i3 are inserted into the horizontal retrace period and transmitted. In the above example, as shown in Figure 2e, M _i1
= "0", M _i2 = "0", and M _i3 = "1" are transmitted. A signal indicating the overflowed most significant bit position obtained by the statistics counter 4 is led to a transmission mode instruction signal generation circuit 5. The output signal of the transmission mode instruction signal generation circuit 5 is led to the transmission mode instruction signal sending circuit 7, gated with the signal shown in FIG. 6g, and the transmission mode instruction signals M _i1 , M _i2 , M _i3 Insert into period and transmit.

Next, based on the statistics of one horizontal period obtained by the statistics counter 4 and the transmission mode instruction signal generation circuit 5, transmission signals B _i3 , B _i2 , B _i1 of the sequence h _i are generated.
We will explain the part that creates the . The 8-bit signal of the sequence h _i is led to the 8-bit shift register 6 via the 1H memory 3 . The output of the 1H memory 3 is stored in the shift register 6 using the clock shown in FIG. 5a. The signals stored in the shift register 6 are shown in FIG. 7a. On the other hand, in accordance with the statistics for one horizontal period obtained by the statistics counter 4, the transmission mode instruction signal generating circuit 5 generates shift pulses for the shift register 6 as shown in FIG. 5c. FIG. 5c shows the case where the overflowed most significant bit position is b _i7 . In this case, shift register 6 is shifted 4 bits toward the LSB, so the contents of shift register 6 are shifted to the 7th bit.
It will look like Figure b. That is, b _i7 , b _i6 , and b _i5 become the transmission signals of the sequence h _i . The output of the shift register 6 is gated by a gate circuit 8 with the signal shown in FIG. 6f, and b _i7 , b _i6 , b _i5 are transmitted as transmission 3-bit signals B _i3 , B _i2 , B _i1 . As explained above, based on the statistics of one horizontal period, the same
Transmission can be performed by switching the quantization step of the transmission signal in the horizontal period.

Next, the decoding side will be explained using FIG. 4. In FIG. 4, input terminals E, F, and G receive transmission mode instruction signals M _i3 ,
M _i2 and M _i1 are supplied. In addition, input terminal H,
I, J have transmission signals B _i3 , B i2 , B _i2 , of sequence h _i
B _i1 is supplied. Transmission mode instruction signals M _i3 , M _i
2 and M _i1 are held by the mode instruction circuit 9 for one horizontal period. Furthermore, the mode instruction circuit 9 generates a shift clock for the shift register 10 depending on the transmission mode. As mentioned above, when b _i7 , _{b i6 ,} b _i5 are transmitted as B _i3 , B _i2 , B i1 ,
The shift clock is as shown in FIG. 5c. That is, b _i7 , b _i6 , and b _i5 are stored in the lower 3 bits of the shift register 10, but by the shift clock, they are shifted by 4 bits toward the MSB and stored in the correct bit position. . This signal is supplied to the Hadamard inverse transform circuit 11, where it undergoes Hadamard inverse transform and becomes a digital 8-bit signal in the time domain. This 8-bit signal is converted into an analog video signal by the D/A conversion circuit 12 and output to the output terminal G.

As described above, the orthogonal transform coding method of the present invention differs from the conventional example in which the quantization step and number of transmission bits of each sequence are statistically set to certain values, and the orthogonal transform encoding method of the present invention can perform quantization without increasing the number of transmission bits. Since the number of conversion steps is switched, it is possible to prevent overflow and transmit images with less deterioration. In addition, in this orthogonal transform encoding method, the fixed period for detecting statistics and the fixed period for switching the number of quantization steps according to the statistics are the same period, and the previous fixed period and the current fixed period This is different from determining the number of quantization steps for the current fixed period based on the statistics for the previous fixed period, based on the premise that the statistics for the previous fixed period and for the current fixed period are the same. Even if the statistics for a certain period of time are different (normally, the statistics are different for each certain period of time), the quantization step can be switched correctly. In addition, when a certain period of time is defined as one horizontal period, switching is performed every horizontal period, so the response is fast, and for videos that require switching the entire screen, switching can be performed without waiting for the next field. It is possible. Another advantage is that the size of the statistics counter and memory can be small.

On the other hand, when the fixed period is one vertical period, the border line due to switching is not visible on the screen. Also, it has the advantage that it is visually unnoticeable if it is switched in field units. However, the size of the statistics counter and memory increases.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of compressing the bits of each sequence subjected to orthogonal transformation, Fig. 2 is an explanatory diagram of the transmission region when the quantization step is changed with the same number of bits, and Fig. 3 is an example of one example of this invention. FIG. 4 is a block diagram of the encoding side of the embodiment. FIG. 5 is a time chart of the shift registers 6 and 10. FIG. 6 is a waveform diagram of each point in FIG. 3. FIG. 7 is an explanatory diagram of the operation of the shift register 6. 2... Hadamard transform circuit, 3... 1H memory, 4... Statistics counter, 5... Transmission mode instruction signal generation circuit, 6... Shift register, 7...
Transmission mode instruction signal sending circuit, 8...gate circuit.

Claims (1)

[Scope of Claims] 1. Detecting the statistics of each sequence obtained by orthogonal transformation during a certain period of time, delaying each of the sequences by a time width of the certain period using a delay means, and detecting the statistics in accordance with the statistics. The orthogonal method is characterized in that the number of transmission bits of each sequence during the fixed period delayed by the delay means is fixed and the number of quantization steps is changed, thereby changing the amplitude range to be transmitted. Transform encoding method. 2. The unit period for detecting the statistics of each sequence is one vertical period, and an instruction signal for switching the number of quantization steps is inserted in the vertical retrace period. Orthogonal transform encoding method. 3. The unit period for detecting the statistics of each sequence is one horizontal period, and an instruction signal for switching the number of quantization steps is inserted into the horizontal retrace period. Orthogonal transform encoding method.