JPH0276472A - Picture expanding system - Google Patents

Abstract

PURPOSE:To expand the arbitrary magnification by reading a picture signal in units of a block, executing the two-dimensional discrete cosine transform setting an expanded block, executing the reverse discrete cosine transform and generating an output picture signal. CONSTITUTION:When a picture is expanded, a block reading means 1 read a picture signal in units of the block to execute the two-dimension discrete cosine transform. A DCT transforming means 2 executes the two-dimensional discrete cosine transform of the picture signal for one read block and calculates a transform coefficient 102. Next, the size of the expanded block is set to an expanding block size setting means 3 and outputted to an expanding block preparing means 4 and a reverse DCT transform means 5. The means 4 matches the transform coefficient 102 to the low area side of an expanding block, and with the remaining transform coefficient as 0, an exchange coefficient 104 included in the expanding block is prepared. The means 5 execute the reverse discrete cosine transform of the transform coefficient 104 included in an expanding block, calculates the expanding picture signal and a block writing means 6 outputs this.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an image enlargement method for enlarging an image.

(Prior Art) A linear interpolation method is one of image enlargement methods for multivalued images (for example, 8 bits per pixel, 256 levels).

In this method, an enlarged image is obtained by linearly interpolating between the pixels of the original image to generate a number of pixels according to the enlargement ratio.

(Problems to be Solved by the Invention) In the conventional enlarging method using linear interpolation, when enlarging a multivalued image by an integral number of times, the enlarged image can be obtained relatively easily by linear interpolation. However, if an attempt is made to enlarge the image at a magnification that is not an integer, an enlarged image cannot be easily obtained if the image is generated by linear interpolation between the pixels of the original image.

An object of the present invention is to provide an image enlarging method that can easily obtain an enlarged image of any magnification. - (Means for solving the problem) The image enlarging method of the present invention reads out an image signal in units of blocks each consisting of a plurality of pixels, and performs orthogonal transformation for converting from the spatial domain to the frequency domain in units of blocks. Give,
A first transform coefficient matrix consisting of a plurality of transform coefficients is determined, a second transform coefficient matrix corresponding to an enlarged block larger than the above block is set, and the transform coefficients of the first transform coefficient matrix are set on the low frequency side. The method is characterized in that the remaining transform coefficients are set to 0, the values of the second transform coefficient matrix are determined, and the second transform coefficient matrix is subjected to inverse orthogonal transformation.

(effect) The image enlargement method of the present invention will be explained.

First, image signals are read out in blocks each consisting of a plurality of pixels. As this block, a square block consisting of nXn pixels is often used, but a rectangular block consisting of mXn pixels can also be used.

Next, a two-dimensional discrete cosine transform is applied to each block to obtain a plurality of transform coefficients. If a square block consisting of nXn pixels is used, the plurality of transform coefficients will also be nXn per block.

Note that here we use a two-dimensional discrete cosine transform as the orthogonal transform, but there are also other orthogonal transforms that transform from the spatial domain to the frequency domain, such as the Hadamard transform.
Any orthogonal transformation can be used.

On the other hand, at the time of output, an enlarged block larger than the block at the time of input is set. As for the transform coefficients constituting this enlarged block, the transform coefficients in the input block are applied to the low frequency side of the enlarged block, and 0 is set to the other parts. Usually, a square block consisting of MXN transform coefficients is used as this enlarged block, but a rectangular block consisting of MXN transform coefficients can also be used.

The transform coefficients in this enlarged block are subjected to inverse discrete cosine transform to generate an image signal. However, as this inverse discrete cosine transform, an inverse discrete cosine transform corresponding to the size of the enlarged block is performed. That is, as an enlarged block M
When a square block consisting of XN transform coefficients is used, an output image signal consisting of NXN pixels is generated by performing an inverse discrete cosine transform corresponding to the size of NXN.

Since the size of this enlarged block is larger than the size of the input block, the output image signal becomes an enlarged image. Here, the block size at the time of input is nXn
When the size of the enlarged block is NXN, the output image signal becomes an image obtained by enlarging the original image signal at a ratio of n:N both vertically and horizontally.

Generally, when the input block size is mXn and the expanded block size is MXN, the output image signal is the original image signal that is expanded in the horizontal direction at a ratio of m:M and the vertical direction is n.
The image is enlarged at a ratio of :N.

Such an output image signal is outputted in units of enlarged blocks to obtain an overall output image signal.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the image enlargement method of the present invention. As shown in FIG. 1, when enlarging an image, first, the block readout means 1 reads out the image signal in units of blocks that undergo two-dimensional discrete cosine transformation.

For example, an image signal of 8 bits per pixel is read out as one block of 64 pixels in total, 8 pixels vertically and 8 pixels horizontally.

Then, the DCT transformation means 2 performs two-dimensional discrete cosine transformation on the read image signal 101 for one block, and
x8 conversion coefficients 102 are calculated. The calculation formula for this two-dimensional discrete cosine transformation is as follows.

2n 2n However, n=8 f(ij): Image signal (ij=0.1.-, n-1
)F(u,v): Conversion coefficient (u,v=0,1.-,n-
1).

Next, the enlarged block size is set in the enlarged block size setting means 3, and the enlarged block generating means 4 and inverse DCT are performed.
It is output to the conversion means 5.

FIG. 2 is an explanatory diagram showing a method of setting enlarged blocks. For example, the size of the expansion block in this case is l0XI
It is O. As shown in FIG. 2, the enlarged block generating means 4 applies the transform coefficient 102 to the low frequency side of the enlarged block based on the enlarged block size 103 outputted from the enlarged block size setting means 3, and the remaining transform coefficients 0
The transform coefficients 104 included in the enlarged block are generated and output.

Then, the inverse DCT transform means 5 performs inverse discrete cosine transform on the transform coefficients 104 included in the enlarged block for each enlarged block, and calculates and outputs an enlarged image signal 105 of loXIO pixels. This inverse discrete cosine transformation is performed with the size set by the enlarged block size setting means 3. Here, it is a 10×10 two-dimensional discrete cosine transform, and the calculation formula is as follows.

2N 2N However, N=10 G (u, v): Transform coefficient in the enlarged block (u, v=0
．． 1. -, N-1N -1), j): Enlarged image signal (i, j = 0, 1.
..., N-1).

The enlarged image signal 105 obtained in this way has loXIO pixels for each enlarged block. At the time of input, the image signal of 8 x 8 pixels was subjected to discrete cosine transform for each block, so the enlarged image signal 105 has an image signal of 8:10 both vertically and horizontally.
The image is enlarged to .

Finally, the block writing means 6 includes the inverse DCT transformation means 5
Enlarged image signal 105 in units of enlarged blocks output from
is output to an image output device such as an image display device or an image recording device.

In this way, since the inverse discrete cosine transform is performed using the size of the enlarged block, an enlarged image of any magnification can be easily obtained.

In addition, in the above explanation, the block size at the time of input is 8x8, and the enlarged block size at the time of output is 10XIO.
However, other sizes and shapes may be used. For example, if the input block size is mXn and the output enlarged block size is MXN, then
The enlarged image signal 105 is an image obtained by enlarging the original image signal in the horizontal direction at a ratio of m:M and in the vertical direction at a ratio of n:N.

In this way, it is possible to freely set the magnification ratio, and since the magnification ratios in the vertical and horizontal directions can be set independently, it is possible to deal with various cases.

Also, here we used a two-dimensional discrete cosine transform as the orthogonal transform, but any other orthogonal transform that transforms from the spatial domain to the frequency domain, such as the Hadamard transform, can be used. Can be done.

In addition, in the above explanation, image signals are not particularly defined, but multivalued black and white images, RGB color component images, luminance/color difference signals such as Y, (RY), (B-Y), etc. are all included in this image signal. Similarly, the present invention can be applied to inter-frame difference signals in moving images such as television signals, and sufficient effects can be obtained. Regarding this inter-frame difference signal, refer to the reference document: r T
e1evision BandwidthComprehensive
ssion transmission by Mot
ion-compensatedInterframe
Coding J IEEE Communica
tion Magazine, November 1982 issue, 2
It is described in detail on pages 4-30.

(Effects of the Invention) As described above, by using the image enlarging method and device of the present invention, it is possible to easily enlarge an image to any desired magnification.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the image enlargement method of the present invention, and FIG. 2 is an explanatory diagram showing a method of generating an enlarged block. In the figure, 1... Block reading means, 2... DCT transformation means, 3... Enlarged block size setting means, 4... Enlarged block generation means, 5... Inverse DCT transformation means, 6.
...Block writing means.

Claims (1)

[Claims] The image signal is read out in blocks each consisting of a plurality of pixels, and an orthogonal transformation for converting from the spatial domain to the frequency domain is applied to each block to obtain a first transform coefficient row example, and the image signal is converted into an enlarged block larger than the above block. Set a corresponding second transform coefficient matrix, apply the transform coefficients of the first transform coefficient matrix to the low frequency side of the second transform coefficient matrix, set the remaining transform coefficients to 0, and perform the second transform. An image enlargement method characterized by determining values of a coefficient matrix and performing inverse orthogonal transformation on this second transformation coefficient matrix.