JP2624013B2 - Image coding method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding method and apparatus for compressing, transmitting, and recording digital images.

[0002]

2. Description of the Related Art The transfer rate of digital images is several hundreds or more.
When the transmission rate reaches several Gbps, the communication cost becomes high to transmit at the same transfer rate, and the recording capacity becomes insufficient for recording. Therefore, conventionally, an image encoding method and apparatus have been developed in which the deterioration of the image quality is minimized and the transfer rate is reduced.

A two-dimensional motion compensated frame difference DCT, which is an example of the above-described conventional image coding method and apparatus, will be described below with reference to the drawings.

FIG. 5 is a block diagram of a two-dimensional DCT between motion compensation frames, and FIGS. 6 to 9 are explanatory diagrams for explaining the operation of the two-dimensional DCT between motion compensation frames. is there. In FIG. 5, 50 is an image input terminal, 51 is a DCT circuit, 52 is a quantizer, 53 is an inverse quantizer, 54 is an inverse DCT circuit, 55 is a frame memory,
6 is a motion compensation inter-frame prediction circuit, 57 is a motion detection circuit, 58 is an intra-field / inter-field switching signal input terminal, and 59 is a coded image output terminal.

[0005] The operation of the image coding apparatus configured as described above will be described below. It is assumed that the input image is interlaced scanned. FIG. 6 shows a temporal and spatial arrangement diagram of pixels of the input image, in which the horizontal axis represents the time direction and the vertical axis represents the vertical direction, that is, the line direction. Pixels are arranged at positions shifted in time by one vertical line as shown in FIG. In the figure, a set of pixels having the same time axis is generally referred to as a field, and two fields having different time axes are generally referred to as a frame. For example, a frame t includes field 1 and field 2.

[0006] The image coding apparatus shown in FIG. 5 is coded on a field-by-field basis. FIG. 7 is an explanatory diagram of an encoding method when the image of FIG. 6 is input. The image of the first frame of the encoding, that is, the image of the frame t, is intra-field encoded for each field without taking a difference by the switching signal indicating the intra-field encoding input to the input terminal 58. That is, the image data is stored in the DCT circuit 5 in a certain block unit.
The transform coefficient is converted into a transform coefficient by 1, the transform coefficient is quantized by a quantizer 52, and transmitted to a transmission line from an encoded image output terminal 59.
Since an image generally has a high correlation, when DCT is performed, energy is concentrated on transform coefficients corresponding to low frequency components. Therefore, it is possible to minimize image quality degradation and reduce the amount of data by quantifying high frequency components that are not visually conspicuous and finely quantizing low frequency components that are important components. The transform coefficients sent to the transmission line are simultaneously dequantized by the inverse quantizer 53 and the inverse DCT transform circuit 5.
The data is returned to the real-time data through 4 and stored in the frame memory 55.

On the other hand, the image after the (t + 1) frame is
Inter-frame difference encoding is performed for each field. First, an inter-frame motion vector is obtained for each block in the motion detection circuit 57 using, for example, a well-known full search method. The term “between frames” means that the first field of the t frame performs motion detection with the first field of the (t + 1) frame, and the second field of the t frame performs motion detection with the second field of the (t + 1) frame. The motion compensation inter-frame prediction circuit 56 uses the detected motion vector to generate a motion-compensated prediction value of the next frame in block units. The (t + 1) frame image is obtained by taking a difference from a predicted value generated from the t frame, and thereafter, is encoded for each field in the same manner as the t frame. (T
After the (+2) frame, the prediction value is encoded in the same manner as in the (t + 1) frame. According to the above method, since the difference from the predicted value is encoded, the energy is reduced as compared with the case where no prediction is performed, so that more efficient encoding becomes possible (for example, Hatori, Hashimoto, "Video coding method", Journal of the Institute of Television Engineers of Japan Vol.44, No.1, pp47
~ 54 (1990)).

[0008]

However, in the above configuration, the correlation in the vertical direction cannot be used because the field is a unit. As shown in FIG. 6, the fields have different time-space positions, but generally the images between the fields have a high correlation. For example, in a still image,
The image does not change even if the time is different, and considering the x, y, and z points in FIG.
The correlation between the x and y points is higher. Then, as shown in FIG. 8, it is conceivable to combine the field 1 and the field 2 to form a frame, and encode the combined frame as a unit. However, in a frame in which fields are simply combined, as shown in FIG. 9, in the case of an image having a large motion, a portion where the correlation in the vertical direction is reduced occurs, which causes deterioration in image quality during encoding. Had a point.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an image encoding method and apparatus which does not cause deterioration in image quality even for an image having large motion and is highly efficient.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to input interlaced-scanned image data, detect an inter-field motion vector of the image data, and use the inter-field motion vector. A motion-compensated frame is formed by performing inter-field motion compensation, and the motion-compensated frame is subjected to block coding.

[0011]

According to the present invention, since the coding is performed in frame units after the vertical correlation is enhanced by performing the motion compensation between fields by the above-described configuration, the image coding can be performed with high efficiency without deteriorating the image quality even in a large motion part. Can be done.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image encoding method and apparatus according to one embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an image encoding apparatus according to a first embodiment of the present invention, FIG. 2 is an explanatory diagram of a method for compensating motion between fields, and FIG. 3 is a diagram of FIG. It is a detailed block diagram of the motion detection circuit and the inter-field motion compensation circuit shown. In FIG. 1, reference numeral 1 denotes a motion detection circuit, 2 denotes an inter-field motion compensation circuit, and 3 denotes a block coding circuit.

The image coding apparatus configured as described above will be described below with reference to FIG. 1 and FIG.

In the input image, a motion detection circuit 1 obtains a motion vector between fields in block units by a block matching method. Next, the obtained motion vector of each block is averaged for all the blocks in the field, and the average value is used as an inter-field motion vector. The inter-field motion compensation circuit 2 uses the inter-field motion vector
Perform motion compensation between fields to create a motion compensated frame. FIG. 2 shows an example of a motion-compensated frame, in which the motion of an object between fields as shown in FIG. 9 is compensated, and a frame having a high vertical correlation is formed. The block coding circuit 3 performs block coding on the motion-compensated frame in frame units. In FIG. 1, an inter-frame difference two-dimensional DCT encoding device having the same configuration as that of the conventional example is used as a block encoding circuit. In the figure, reference numerals 51 to 58 perform the same operation as the conventional example, but the difference from the conventional example is that the processing is performed on a frame basis. Compared to the field-based processing, the motion-compensated frame-based processing reduces the vertical pixel-to-pixel distance by half, so that the correlation increases and the DCT efficiency increases. As a result, an encoding device with higher efficiency than the conventional example can be obtained. In addition, since motion compensation is performed between fields, encoding can be performed on an image having a large motion without lowering the efficiency.

FIG. 3 is an example of a detailed configuration diagram of the motion detection circuit 1 and the inter-field motion compensation circuit 2 described above. The motion detection circuit 1 includes a frame memory 11 for storing an input image, an address generation circuit 12 for generating an address thereof, a square error calculation circuit 13 for calculating a square error between blocks in different fields, and a square error calculation. Circuit 13
Among the square errors calculated in the above, the block address of the block with the smallest error among the square errors is output as a motion vector, and the motion vector of each block generated by the minimum error selection circuit 14 is input. The average value calculating circuit 15 outputs the inter-field motion vector by averaging the motion vectors of the blocks.

The motion compensating circuit 2 stores an input image, performs inter-field motion compensation, inputs a frame memory 21 for outputting a motion-compensated frame unit, and inputs a motion vector generated by the motion detecting circuit 1. It comprises an address generation circuit 22 for performing an operation for performing inter-field motion compensation by operating an address of the frame memory 11.

FIG. 4 is a block diagram of an image coding apparatus according to a second embodiment of the present invention. The difference from the first embodiment is that the motion estimation circuit 1 and the motion estimation circuit 57 in the block encoding circuit 3 are shared. In the second embodiment, the motion detection circuit 1 detects motion between frames. For motion compensation between fields, a motion vector detected for each block between frames is averaged for all blocks in the frame, and the average value is halved to obtain an interfield motion vector. With the above-described configuration, although the accuracy is slightly lower than when a motion vector between fields is obtained, it is not necessary to have different circuits between fields and between frames. Almost the same effect can be obtained with wear.

In the above-described embodiment, the two-dimensional DCT coding between frames has been described as an example of the block coding. However, the present invention is not limited to this. For block coding, three-dimensional DCT, vector quantum It can be used for anything such as chemical conversion.

In the above embodiment, the inter-field motion vector is obtained by averaging the motion vectors of all the blocks in the field or the frame. However, the present invention is not limited to this. Or consider the field or frame as one block,
Various methods are available, such as detecting one inter-field motion vector from the beginning.

[0021]

As described above, according to the present invention, an inter-field motion vector of image data is detected, and inter-field motion compensation is performed using the detected inter-field motion vector to form a motion-compensated frame. In order to construct a block with high vertical correlation and perform block coding by performing block coding on the motion compensated frame,
Highly efficient image encoding can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image encoding device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a motion compensation method between fields according to the present invention.

FIG. 3 is a detailed block diagram of a motion detection circuit and a field motion compensation circuit according to the present invention.

FIG. 4 is a block diagram of an image encoding device according to a second embodiment of the present invention.

FIG. 5 is a block diagram of a conventional motion-compensated inter-frame difference two-dimensional DCT.

FIG. 6 is an explanatory diagram illustrating an operation of a motion compensation inter-frame difference two-dimensional DCT.

FIG. 7 is an explanatory diagram for explaining an operation of a motion compensation inter-frame difference two-dimensional DCT.

FIG. 8 is an explanatory diagram for explaining the operation of the motion compensation inter-frame difference two-dimensional DCT.

FIG. 9 is an explanatory diagram for explaining the operation of the motion-compensated inter-frame difference two-dimensional DCT.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Motion detection circuit 2 Inter-field motion compensation circuit 3 Block encoding circuit 11 Frame memory 12 Address generation circuit 13 Square error calculation circuit 14 Minimum error selection circuit 15 Average value calculation circuit 21 Frame memory 22 Address generation circuit

Claims (4)

(57) [Claims] 1. An interlaced scanned image data is input, an inter-field motion vector of the image data is detected, and inter-field motion compensation is performed using the inter-field motion vector to form a motion-compensated frame. An image encoding method, which comprises encoding a motion-compensated frame with a block. 2. An inter-field motion vector is obtained by detecting N motion vectors between fields (N: an integer satisfying N ≧ 1) and averaging the detected N motion vectors. Item 7. The image encoding method according to Item 1. 3. An inter-field motion vector, wherein N motion vectors are detected between frames (N is an integer satisfying N ≧ 1), and the detected N motion vectors are averaged to obtain an average value n. 2. The image encoding method according to claim 1, wherein the average value n is obtained by halving the average value n. 4. A motion-compensated frame which receives interlaced scanned image data and detects an inter-field motion vector of the image data, and performs inter-field motion compensation using the detected inter-field motion vector. And a block coding circuit for block coding the motion-compensated frame.