JP2892701B2 - Video signal encoding device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for encoding a moving image signal used for a videophone, a video conference, or the like.

2. Description of the Related Art A conventional high-efficiency video signal encoding apparatus performs motion-compensated inter-frame prediction and intra-frame prediction, or performs one of the motion-compensated inter-frame prediction and intra-frame prediction. Alternatively, a prediction error value is calculated by performing prediction for selectively switching between the motion compensated inter-frame prediction and the intra-frame prediction, and the prediction error value is calculated for each block which is a set of a plurality of pixels (for example, 8 × 8). Are known that perform orthogonal transform on the coefficients and encode the coefficients.

FIG. 3 shows a configuration of a conventional high-efficiency encoding apparatus for a moving image signal.

In FIG. 3, the analog video signal is an A / D converter 1
Is converted into a digital video signal by the motion vector detection circuit 2 using the digital video signal and the reproduced pixel value of the previous frame read from the frame memory 3 to form a plurality of pixels (for example, 8 × 8). Is calculated for each block, which is a set of.

The prediction circuit 4 performs prediction in which motion-compensated inter-frame prediction and intra-frame prediction are mixed using the motion vector and the reproduced pixel values of the current frame and / or the previous frame read from the frame memory 3, The prediction value is calculated by performing either one of the motion-compensated inter-frame prediction and the intra-frame prediction, or performing the prediction for selectively switching between the motion-compensated inter-frame prediction and the intra-frame prediction.

The subtractor 5 calculates a prediction error value by subtracting the prediction value from the digital video signal from the A / D converter 1, and the orthogonal transformation circuit 6 calculates the prediction error value as a block which is a set of a plurality of pixels. Each time, the coefficient is calculated by performing an orthogonal transform, and then the coefficient quantization circuit 7 executes the quantization step width control circuit 15.
, The orthogonal transform coefficient is quantized with the quantization step width determined by, and the quantized coefficient encoding circuit 8 encodes the quantized orthogonal transform coefficient.

The code of the quantized orthogonal transform coefficient is transmitted by the line encoding circuit 13 together with the quantization step width determined by the quantization step width control circuit 15 and the motion vector detected by the motion vector detection circuit 2. The speed is smoothed by the transmission buffer 14 and transmitted to the line. The quantization step width control circuit 15 includes a transmission buffer
When the residual information amount is large, the quantization step width is increased to suppress the generated information amount, and when the residual information amount is small, the quantization step width is reduced and the image is transmitted finer.

The code of the quantized orthogonal transform coefficient is locally decoded by a quantization coefficient decoding circuit 9, and then, by a coefficient inverse quantization circuit 10, a quantization step determined by a quantization step width control circuit 15. The width is inversely quantized into orthogonal transform coefficients. Further, the prediction error value is reproduced by the orthogonal inverse transform circuit 11, and the prediction error value is added to the prediction circuit 4 by the adder 12.
The pixel value is reproduced by adding the prediction value from
The data is written to the frame memory 3.

Therefore, according to the above conventional example, by adaptively controlling the quantization step width according to the amount of residual information in the transmission buffer 14, for example, at a constant frame such as 64 Kb / s, 384 Kb / s, etc., at a variable rate It is also possible to transmit a moving image with little image quality deterioration.

However, in the above-described conventional moving picture signal encoding apparatus, when noise is superimposed on the input signal, the noise is encoded in the same manner as the image signal, and therefore, the effective signal is effective. There is a problem that the amount of information for transmitting an image signal is reduced, and a reproduced image is deteriorated.

The present invention has been made in view of the above-described conventional problems, and when noise is superimposed on an input signal, the amount of information for transmitting an effective image signal does not decrease, and thus a reproduced image can be improved. An object of the present invention is to provide a video signal encoding device.

Means for Solving the Problems In order to achieve the above object, the present invention considers that when noise is superimposed on an input signal, the influence of noise increases near the boundary of the quantization characteristic, The corresponding threshold value and the value of the orthogonal transform coefficient are compared in block units. As a result, when it is determined that the block is significant, the orthogonal transform coefficient is quantized, and when it is determined that the block is insignificant, all orthogonal transform coefficients of the block are quantized. This is set to “0”.

Further, as a method of determining a significant block or a non-significant block, a threshold value and a value of an orthogonal transform coefficient are compared in units of a block in accordance with a quantization characteristic, and an orthogonal transform coefficient at a predetermined position in the block is larger than the threshold value. A case where the value is larger is a significant block, and a case where the value of the orthogonal transform coefficient at a predetermined position is smaller than the threshold value is a non-significant block.

Operation According to the present invention, it is possible to reduce encoding of noise by the above-described configuration. Therefore, the amount of information for transmitting an effective image signal does not decrease and a reproduced image can be improved.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a moving picture signal coding apparatus according to the present invention, and FIG. 2 is an explanatory diagram showing characteristics of the coding apparatus shown in FIG.

In FIG. 1, 1 is an A / D converter for converting an analog moving image signal into a digital moving image signal, and 2 is a digital moving image signal from the A / D converter 1 and before being read from the frame memory 3. This is a motion vector detection circuit that calculates a motion vector for each block, which is a set of a plurality of pixels (for example, 8 × 8), using a reproduced pixel value of a frame.

4 uses the motion vector and the reproduced pixel values of the current frame and / or previous frame read from the frame memory 3 to perform prediction in which motion-compensated inter-frame prediction and intra-frame prediction are mixed, A prediction circuit that calculates a prediction value by performing either inter-frame prediction or intra-frame prediction, or performing prediction for selectively switching between the motion compensated inter-frame prediction and intra-frame prediction.

5 is a subtractor for calculating the prediction error value by subtracting the prediction value from the digital video signal from the A / D converter 1;
Reference numeral 6 denotes an orthogonal transformation circuit that performs orthogonal transformation on the prediction error value for each block, which is a set of a plurality of pixels, and calculates a coefficient thereof.

Reference numeral 16 indicates whether the block orthogonally transformed by the orthogonal transformation circuit 6 is a significant error block or a non-error block based on the orthogonal transformation coefficient calculated by the orthogonal transformation circuit 6 and the quantization step width determined by the quantization step width control circuit 15. A significant / insignificant error block determination circuit that determines whether the block is a significant error block and switches the switch 17 based on the determination result.

7a is a coefficient quantization circuit that quantizes the orthogonal transform coefficient or “0” with the quantization step width determined by the quantization step width control circuit 15, and 8 encodes the quantized orthogonal transform coefficient. Is a quantization coefficient coding circuit.

9 is a quantization coefficient decoding circuit for locally decoding the code of the quantized orthogonal transform coefficient from the quantization coefficient coding circuit 8, and 10 is a quantization step determined by the quantization step width control circuit 5. A coefficient inverse quantization circuit for inversely quantizing to an orthogonal transform coefficient by the width; 11, an orthogonal inverse transform circuit for reproducing a prediction error value using the orthogonal transform coefficient; An adder for reproducing the pixel value by adding the values and writing the pixel value to the frame memory 3
It is 12.

Reference numeral 13 denotes a code of the quantized orthogonal transform coefficient from the quantization coefficient coding circuit 8, the quantization step width determined by the quantization step width control circuit 15, and the motion detected by the motion vector detection circuit 2. A line coding circuit for line coding a vector is a transmission buffer for speed-smoothing the code from the line coding circuit 13 and sending it out to the line, and a quantization step width control circuit 15 When the amount of information is large, the amount of generated information is suppressed by increasing the quantization step width, and when the amount of residual information is small, the image is finely transmitted by reducing the quantization step width.

Next, the operation of the above embodiment will be described with reference to FIG.

First, when noise is superimposed on the input signal, a characteristic pattern appears in the orthogonal transform coefficient of the prediction error calculated by the orthogonal transform circuit 6. That is, when white noise is superimposed, noise is superimposed on all orthogonal transform coefficients, and when flicker noise is superimposed, noise is superimposed on a specific orthogonal transform coefficient.

Next, considering the increase in the amount of transmission information due to quantization characteristics and noise, generally, when the amount of transmission information increases due to noise for a certain quantization characteristic, the value input to the coefficient quantization circuit 7a is This is the case near the boundary of the region determined by the quantization characteristic.

For example, when the quantization characteristics are as shown in FIG.
Depending on whether the input value is Th−δ or Th + δ (δ> 0), the output value is “0” or “Th + g / 2”. This quantization characteristic has a large effect when noise is superimposed on input values near Th, Th + g, and Th + 2g.

As described above, according to the above-described embodiment, the significant block and the non-significant block are determined using the orthogonal transform coefficient that can directly determine the increase in the amount of information generated due to noise and the threshold corresponding to the quantization characteristic. In addition, the amount of information generated in a block where the amount of generated information is likely to increase due to noise can be suppressed.

Next, another embodiment of the above method of determining a significant / insignificant block will be described. The significant / insignificant error block determination circuit 16 uses the step width g determined by the quantization step width control circuit 15 and the orthogonal transformation coefficient C _ij calculated by the orthogonal transformation circuit 6 to set a threshold Th Th = α × g. 1) Calculate α is a constant.

Next, when C _ij ≦ Th (2) with respect to the orthogonal transformation coefficient value C _ij of the block, the block is determined to be a non-error block, and when the equation (2) is not satisfied, the block is determined. Judge as a significant error block.

When the block is determined to be a non-significant error block, the coefficient quantization circuit 7a controls the switch 17 so as to quantize “0”, and when the block is determined to be a significant error block, the coefficient quantization circuit 7a The switch 17 is controlled so that the coefficient calculated by the circuit 6 is quantized.

Therefore, according to the above embodiment, since the threshold value Th proportional to the quantization step width g is calculated, an increase in the amount of information transmitted by superimposed noise is suppressed according to the value of the quantization step width g. be able to.

Further, according to the above embodiment, since the threshold value Th is compared with all the values of the orthogonal transform coefficients C _ij of the block, it is possible to suppress an increase in the amount of information transmitted by white noise.

Note that, instead of comparing the values of all the orthogonal transform coefficients C _ij of the block with the threshold Th, the orthogonal transform coefficients at a predetermined position are compared with the threshold Th, so that the block is transmitted by the noise of the frequency component having a certain characteristic. An increase in the amount of information can be efficiently suppressed.

Effect of the Invention As described above, the present invention considers that when noise is superimposed on an input signal, the influence of noise increases near the boundary of the quantization characteristic, The values of the transform coefficients are compared in units of blocks, and when they are determined to be significant blocks, the orthogonal transform coefficients are quantized, and when they are determined to be insignificant blocks, the orthogonal transform coefficients of all the blocks are quantized to "0". Therefore, encoding of noise can be reduced, and therefore, the amount of information for transmitting an effective image signal does not decrease and a reproduced image can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a moving picture signal coding apparatus according to the present invention, FIG. 2 is an explanatory diagram showing characteristics of the coding apparatus shown in FIG. 1, and FIG. 1 is a block diagram showing a moving picture signal encoding device. DESCRIPTION OF SYMBOLS 1 ... A / D converter, 2 ... Motion vector detection circuit, 3 ... Frame memory, 4 ... Prediction circuit, 5 ... Subtractor, 6 ... Orthogonal conversion circuit, 7a ... Coefficient quantization circuit, 16 ... Significant / insignificant error Block judgment circuit, 17 ... switch.

Claims (2)

(57) [Claims] 1. A means for calculating a prediction value for an input pixel based on a frame correlation of an input image signal, and calculating a prediction error between the input pixel value and the prediction value; Means for calculating the orthogonal transform coefficient, and a threshold value corresponding to the characteristic of the quantizing means and the value of the orthogonal transform coefficient are compared in block units. As a result, when it is determined that the block is significant, Means for quantizing the orthogonal transform coefficients and controlling all orthogonal transform coefficients of the block to be "0" when the block is determined to be a non-significant block. 2. The control means according to claim 1, wherein each block is determined to be a significant block when the value of the orthogonal transform coefficient at a predetermined position is greater than said threshold value, and is determined when said orthogonal transform coefficient value is smaller than said threshold value. The moving picture signal encoding apparatus according to claim 1, wherein the coding is performed by determining the block as a non-significant block.