JPH07154759A - Adaptive interpolation device for digital signal - Google Patents

Abstract

PURPOSE:To interpolate thinned picture elements by interpolation processing corresponding to a detected direction by detecting the direction significant in correlation by using only the peripheral transmitted picture elements without requiring the transmission of auxiliary information to instruct the interpolation processing. CONSTITUTION:A blocking circuit 2 constitutes a block consisting of the plural transmitted picture elements in the periphery of the thinned picture elements to be interpolated. Concerning the pair of two picture elements respectively horizontally positioned inside a block, a correlation discriminating circuit generates a differential value between these two picture elements and also generates a differential value between two picture elements concerning the vertical direction. The direction significant in correlation at the block is detected by using the horizontal and vertical differential values obtained in the block. An interpolating circuit 3 enables horizontal 1/2 average interpolation, vertical 1/2 average interpolation and 1/4 average interpolation for peripheral four points and selects one of the outputs of these interpolation processings corresponding to the correlation discriminated result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adaptive interpolation apparatus for a digital image signal which is applied to receive a sub-sampling signal and interpolate a thinned pixel.

[0002]

2. Description of the Related Art As one method for band compression or information amount reduction when recording or transmitting a digital image signal, there is a method of reducing the amount of transmission data by thinning out pixels by subsampling. One example is the multiple sub-Nyquist sampling encoding method in the MUSE method. In this system, it is necessary to interpolate non-transmitted pixels that have been decimated on the receiving side.

Offset subsampling is known as an example of subsampling. An example of two-dimensional offset subsampling is shown in FIG. The sampling interval (T) in the horizontal direction (x direction) and the vertical direction (y direction)
x, Ty) is set to twice the pixel interval (Hx, Hy) in the original signal, and every other pixel is thinned out (thinned pixel is indicated by x), and adjacent transmission pixels (indicated by ○) in the vertical direction are set. The offset is half the sampling interval (Tx / 2). As shown in FIG. 7, the transmission band obtained by performing such offset sub-sampling can widen the horizontal or vertical spatial frequency component with respect to the diagonal spatial frequency.

When the offset sub-sampled image signal is displayed on a monitor or printed out, it is necessary to interpolate thinned pixels from adjacent pixels, as shown in FIG. This interpolation processing functions as a spatial filter that allows the frequency components in the shaded area shown in FIG. 7 to pass and blocks the frequency components in the area including the folding point A, and this interpolation processing is based on sampling theory. Is positioned as a post filter.

By the way, the offset sub-sampling as described above is a very effective method when the pre-filter before sampling correctly performs the filtering process. If the pre-filter cannot be applied sufficiently, or if the pre-filter is not applied sufficiently to widen the transmission band, the problem of image quality deterioration due to aliasing distortion occurs.

In order to reduce the occurrence of the above-mentioned folding distortion,
Adaptive interpolation methods have been proposed. This is a method in which the optimum interpolation method is determined in advance during subsampling, and the determination result is transmitted or recorded as auxiliary information. For example, which one of the horizontal half average value interpolation and the vertical half average value interpolation is closer to the true value is detected at the time of sub-sampling and transmitted as 1 bit of auxiliary information per pixel. However, at the time of interpolation, interpolation processing is performed according to this auxiliary information.

[0007]

In the above-described adaptive interpolation method using the auxiliary information, it is necessary to transmit the auxiliary information in addition to the transmission pixels, which causes a problem that the compression rate of the data amount decreases. Further, when an error occurs in the auxiliary information in the process of transmission or recording / reproduction, there is a drawback that the reproduced image is likely to be deteriorated because incorrect interpolation is performed.

Therefore, an object of the present invention is to provide a digital image signal capable of performing high-performance interpolation without the need to transmit auxiliary information when adaptively interpolating pixels thinned out by subsampling. To provide an adaptive interpolator.

[0009]

SUMMARY OF THE INVENTION According to the present invention, an adaptive interpolator for receiving a digital image signal in which predetermined pixels are thinned out by sub-sampling and interpolating the thinned-out pixels is used. A correlation determination circuit for detecting a strongly correlated direction of a local image including a thinned pixel using a plurality of transmission pixels in the periphery,
The interpolation value of the thinned pixel can be generated by a plurality of interpolation processes corresponding to the direction of the correlation checked by the correlation determination means, and the interpolation means for outputting the interpolation value corresponding to the detection result of the correlation determination means. This is an adaptive interpolation device for digital image signals.

[0010]

By using only the transmission pixels in the input signal, it is possible to detect the strongly correlated direction of the region including the thinned pixel to be interpolated. Therefore, it is not necessary to transmit the auxiliary information, and it is possible to prevent erroneous interpolation due to an error during the transmission of the auxiliary information.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below. In FIG. 1, reference numeral 1 is an input terminal of the offset sub-sampled digital image signal as described above. Specifically, a transmission signal by broadcasting or the like, a reproduction signal from a VTR or the like is supplied to the input terminal 1. Reference numeral 2 denotes a blocking circuit for converting an input signal in the order of the television system raster scan into a signal having a block structure.

The output signal of the blocking circuit 2 is the interpolation circuit 3
And the correlation determination circuit 4. Correlation determination circuit 4
As will be described later, uses pixels that are not decimated (transmission pixels) to determine the direction in which the image of the block has a strong correlation. The correlation determination circuit 4 generates a control signal that indicates the direction of strong correlation, and this control signal is supplied to the interpolation circuit 3.

The interpolating circuit 3 is the same as the interpolating circuit 4 in that
It is configured to be able to perform a plurality of interpolation processes corresponding to each of a plurality of examined directions. Then, one of the plurality of interpolation processes is selected by the control signal from the correlation determination circuit 4. An output image signal in which the thinned pixels are interpolated is taken out to the output terminal 5 derived from the interpolation circuit 3.

The correlation determining circuit 4 determines the direction of strong correlation for each block composed of a plurality of transmission pixels shown in FIG. As shown in FIG. 2, thinned pixels (×
(Indicated by) is the center, and twelve transmission pixels having values of a to l around it form one block.

FIG. 3 shows an example of the correlation judging circuit 4. 1
Reference numeral 1 is an input terminal for a blocked image signal. 12
An input signal is supplied to the difference calculation circuits indicated by H and 12V, respectively. The difference values obtained by the difference calculation circuits 12H and 12V are supplied to the absolute value conversion circuits 13H and 13V, respectively, and the absolute value differences are integrated by the integration circuits 14H and 14V.

The evaluation value He in the horizontal direction from the integrating circuit 14H
Occurs, and the vertical evaluation value Ve is generated from the integrating circuit 14V. These evaluation values He and Ve are used in the comparison circuit 1
5, a control signal is generated at the output terminal 16 of the comparison circuit 15 to instruct the correlation determination result. Difference calculation circuit 12
H, the absolute value conversion circuit 13H, and the integration circuit 14H generate the evaluation value He in the horizontal direction according to the following equation.

He = | l−a | + | a−g | + | d−b | + | k−c | + | c−h |

Difference calculation circuit 12V, absolute value conversion circuit 13V
And the integration circuit 14V generates the evaluation value Ve in the vertical direction according to the following equation.

Ve = | f−b | + | b−i | + | a−c | + | e−d | + | d−j |

The smaller the above-mentioned evaluation value is, the stronger the correlation in the direction is in the image near the interpolation target pixel. The comparison circuit 15 receives the evaluation values He and Ve and determines the direction of correlation. That is, Case 1 (He <Ve); Horizontal correlation is stronger than vertical correlation Case 2 (He>Ve); Vertical correlation is stronger than horizontal correlation Case 3 (He = Ve); Horizontal correlation and vertical correlation are equal

The correlation determination circuit 4 outputs a control signal, for example, a 2-bit digital signal, which can distinguish the above-mentioned three cases. The combination of the values of the two pixels used for the difference calculation for detecting the direction in which the block image has a strong correlation is not limited to the above.

FIG. 4 shows another configuration example of the correlation determination circuit 4. The difference value from the difference calculation circuit 12H is the absolute value conversion circuit 1
It is used as one input of the comparison circuit 15 via 3H. The other input of the comparison circuit 15 is the difference value from the difference calculation circuit 12V passed through the absolute value conversion circuit 13V.

The comparison circuit 15 compares the horizontal difference and the vertical difference with respect to four adjacent pixels as follows. -Comparison of horizontal difference | l-a | and vertical difference | e-d | -Comparison of horizontal difference | a-g | and vertical difference | f-b | -Horizontal difference | d-b | and vertical difference | a- c | Comparison of horizontal difference | k−c | and vertical difference | d−j | Comparison of horizontal difference | c−h | and vertical difference | b−i |

The comparison result of the comparison circuit 15 controls the counter 17. The counter 17 is cleared in the initial state, and when the horizontal difference is smaller than the vertical difference, that is, when the horizontal correlation is stronger than the vertical correlation, the count value c of the counter 17
Is incremented to c + 1. On the other hand, when the vertical difference is smaller than the horizontal difference, that is, when the vertical correlation is stronger than the horizontal correlation, the count value c of the counter 17 is decremented to c-1. Although omitted in FIG. 4, the comparison circuit 1
In order to control the counter 17 in this manner by the output of 5, the counter 17 is configured as an up-down counter, and a circuit for generating a pulse for the addition input or the subtraction input of the counter 17 in response to the comparison signal is provided as an example. Just go.

The above-mentioned five sets of comparison results are serially generated from the comparison circuit 15, and the counter 17 performs the counting operation in response to the results. The final count value of the counter 17 is 5
The comprehensive judgment result by the majority logic of the individual comparison results is shown. That is, case 1 (c>0); horizontal correlation is stronger than vertical correlation case 2 (c <0); vertical correlation is stronger than horizontal correlation case 3 (c = 0); vertical correlation and horizontal correlation are equal

Correlation decision circuit 4 shown in FIG. 3 or FIG.
FIG. 5 shows an example of the interpolation circuit 3 controlled by the control signal from the. A digital image signal from the blocking circuit 2 is supplied to the input terminal 21. Input terminal 2
Three interpolation circuits 22, 23, 24 are connected to 1. The output signals of these interpolation circuits 22, 23, 24 are supplied to the selector 25. The above-mentioned control signal of the correlation determination circuit 4 is supplied to the selector 25 through the input terminal 26. The interpolation output selected by the selector 25 is taken out to the output terminal 27.

The interpolating circuit 22 performs a horizontal ½ average interpolation process. In the case of the pixel array of FIG. 2, the value y of the interpolation pixel is generated by the calculation of y = 1/2 (b + d). The interpolation circuit 23 performs a 1/2 average interpolation process in the vertical direction. In the case of the pixel array in FIG. 2, the value y of the interpolation pixel is set to y
= 1/2 (a + c). Interpolation circuit 24
Is the 1 /
4 Average interpolation processing is performed. In the case of the pixel array of FIG.
The value y of the interpolated pixel is generated by the calculation of y = 1/4 (a + b + c + d).

In case 1 in which the horizontal correlation is stronger than the vertical correlation by the control signal supplied from the correlation determining circuit 4 to the selector 25, the selector 25 selects the interpolation value of the interpolation circuit 22. In case 2 where the vertical correlation is stronger than the horizontal correlation, the selector 25 selects the interpolation value of the interpolation circuit 24. In case 3 in which the horizontal correlation and the vertical correlation are equal, the selector 25 selects the interpolation value of the interpolation circuit 23.

Although not shown, the interpolated value extracted at the output terminal 27 and the transmission pixel are combined to form a digital image signal. Further, the block decomposition circuit forms a digital image signal of raster scanning,
It is supplied to a monitor receiver, VTR, and the like.

Although the above-described embodiment of the present invention performs spatial interpolation, it may further include one that performs motion detection and, in the case of stillness, performs interpolation in the time direction. . The present invention can also be applied to subsampling other than offset subsampling.

[0031]

According to the present invention, the direction of strong correlation is detected using only the transmission pixels in the input signal, and the adaptive interpolation is performed based on the detection result. Therefore, as in the past,
Since it is not necessary to transmit the auxiliary information, the compression rate can be improved, and the interpolation processing can be prevented from being erroneous due to an error during the transmission of the auxiliary information.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a schematic diagram showing the positions of pixels used for adaptive interpolation.

FIG. 3 is a block diagram of an example of a correlation determination circuit.

FIG. 4 is a block diagram of another example of the correlation determination circuit.

FIG. 5 is a block diagram of an example of an interpolation circuit.

FIG. 6 is a schematic diagram showing a structure of two-dimensional offset subsampling.

FIG. 7 is a schematic diagram showing a spatial frequency spectrum of a band that can be transmitted by two-dimensional offset subsampling.

FIG. 8 is a schematic diagram showing an interpolation process.

[Explanation of symbols]

 2 Blocking circuit 3 Interpolation circuit 4 Correlation determination circuit

Claims (3)

[Claims] 1. An adaptive interpolator for receiving a digital image signal in which predetermined pixels are thinned out by subsampling and interpolating the thinned pixels, wherein a plurality of transmission pixels around the thinned pixel to be interpolated are Using the correlation determining means for detecting a strong correlation direction of the local image including the thinning pixels, and a plurality of interpolation processes corresponding to the correlation directions checked by the correlation determining means, An adaptive interpolating device for a digital image signal, comprising: an interpolating means capable of generating an interpolating value and outputting an interpolating value corresponding to the detection result of the correlation determining means. 2. The adaptive interpolating device for a digital image signal according to claim 1, wherein the correlation determining means determines a strong correlation direction based on a difference value between transmission pixels around the thinned pixel. Adaptive interpolator for digital image signals. 3. The adaptive interpolating device for a digital image signal according to claim 1 or 2, wherein the correlation determining means includes, in an area around the thinning pixel, every four adjacent transmission pixels. Correlation determination is performed by comparing a difference value between two pixels in the horizontal direction and a difference value between two pixels in the vertical direction, and a comprehensive determination result is formed by a majority logic of a plurality of correlation determination results. An adaptive interpolator for digital image signals, which is adapted to detect a direction having a strong correlation based on.