RU2339181C1 - Method of additional information transmission at fractal coding of images - Google Patents

Abstract

FIELD: physics, image processing.

SUBSTANCE: invention is related to method of reduction of redundancy of transmitted information. Invention actually consists in creation of method for additional information transmission at fractal coding of images. Transmission of additional information is carried out in the following manner: whenever initial image is compressed with the help of fractal compression method, in indices of domain units orientation binary sequence of three digits is recorded, which represents additional information, then based on this additional information processed domain is turned and brightness coefficients - o and contrast coefficients - s are searched for by method of least squares, which correspond to optimal values, at which the following expression is minimised:

where {d_ij} and {r_ij} accordingly are values of pixels in domain and range areas, as a result of which optimal domain is found with account of inbuilt additional information for coding of range unit, after that indices of domains, coefficients of brightness and contrast, additional information are sent through communication channel. On receiving side additional information is separated and initial image is restored.

EFFECT: creation of method for additional information transmission with fractal coding of images.

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Description

The invention relates to the field of telecommunications, and in particular to the field associated with reducing the redundancy of transmitted information. The reason for this, in essence, is that with the help of modern technologies for encoding and data compression, it is possible to significantly reduce the frequency range required for image transmission.

The transfer of additional information is as follows. When encoding an image using the fractal compression method, additional information is inserted into the domain orientation indices. As a result, they find the optimal domain taking into account the built-in additional information. After embedding additional information, this data, together with information about the indexes of the domain blocks of the original image, the brightness and contrast coefficients, are transmitted through the communication channel. On the receiving side, additional information is extracted and the original image is restored.

In digital video technology, in order to increase the amount of information transmitted, it has already been proposed to replace the scanning data contained in the interval for blanking additional information with a digital signal, for example, with digital audio signals and thereby ensure the transmission of additional information (See Ulrich Schmidt, Digital Video Technology, Franzis Verlag Publishing House, Feldkirchen, 1996) [1].

The closest in technical essence to the claimed method of transmitting additional information in fractal coding of images is the method described in patent No. 2292662, IPC ⁸ H04N 7/08 of 01/27/2007 [2]. The prototype method when encoding an image using the fractal compression method, inserts additional information into the lower digits of the domain block indices. The trial inversion procedure is applied to the remaining digits of the domain indexes of the source image. After embedding additional information and optimizing the domain indices, this data, along with information on the domain orientation indices, brightness and contrast, are transmitted through the communication channel. The disadvantage of the prototype method is that as a result of such an insertion, the space of possible domains for displaying to a rank block was reduced, which reduced the quality of the reconstructed image.

The technical result, the invention is aimed at, is a slight decrease in the quality of the original reconstructed image when transmitting additional information.

To achieve this technical result, the insertion of additional information in the fractal compression method is carried out in the orientation indices of the domain blocks, since in the book. S. Welstead "Fractals and wavelets for compressing images in action." Tutorial. - M .: Triumph Publishing House, 2003, pp. 99-100 [3] indicates that a slight sensitivity to distortion in the transformation indices (domain orientation indices) is a confirmation that these transformations can be completely excluded from the encoding process. This fact was also confirmed by the authors of the application for the invention.

Consider the basic algorithm for fractal coding of images, which is performed as follows [3]:

1. The original image is divided into non-overlapping rank blocks. Rank blocks can be equal, but adaptive partitioning with variable block sizes is more commonly used. This makes it possible to densely fill the small blocks of the image containing small details with rank blocks of small size.

2. Then cover the image with a sequence of domain blocks, possibly overlapping. Domains can be of different sizes.

3. The main computational step in fractal coding is the comparison of the domain and rank domains. For each rank block, find the domain and the corresponding transformation that best covers the rank block. This is usually an affine transformation:

where: s _i is a constant that extends or narrows the range of values of the function f (controls the contrast of the image);

o _i - a constant that increases or decreases the values of grayscale (controls the brightness of the image);

w _i is the affine transformation;

- пространственная составляющая преобразования w_i;

is the spatial component of the transformation w _i ;

f (x, y) - image pixel value with coordinates (x, y).

The affine transformation consists of three stages. First, one of eight basic rotations / reflections (four rotations of 90 degrees and mirror reflection in each orientation) is applied to the selected domain. Secondly, the rotated domain region is compressed to fit the size of the ranking region. And finally, the least squares method calculates the contrast and brightness parameters corresponding to the optimal values at which the expression is minimized:

where: {d _ij } and {r _ij } are the pixel values of the domain and rank domains, respectively.

The computational cost of finding the necessary domain among so many options is too high. The task of defining a domain system is a compromise between the need for a large number of domains to be large enough to enable the selection of the best option for matching the rank block and, at the same time, small enough so that the search process can be carried out in an acceptable time. Continue this process until they reach an acceptable match, or the size of the rank blocks reaches a certain predetermined limit. As a result of the basic algorithm, the domain index, domain orientation index, brightness and contrast are transmitted to the decoder.

In the proposed method, at the first stage of affine transformations, taking into account the embedded additional information, a binary sequence of three digits is written (since the possible number of rotations is eight). Further, taking into account this combination of numbers, the processed domain is rotated and the brightness and contrast coefficients are searched. As a result of this introduction, the number of turns is reduced, which also leads to a decrease in both the search time for a suitable domain and the overall encoding time as a whole.

After embedding additional information as rotation indices, this data along with information on domain block indices, brightness and contrast are transmitted through the communication channel. In the decoder, additional information is extracted and the original image is restored. Image decoding is carried out by iteratively applying the affine transform to an arbitrary initial image. In accordance with the theorem on squeezing mappings, iterations will converge regardless of the choice of the initial image. A compression mapping is defined as a separate transformation for each rank block. Each rank block has a transformation and domain associated with it. The contents of this rank block are computed by applying the transform to the domain block. One iteration ends when all rank blocks are processed.

The claimed method is illustrated by drawings:

figure 1 - affine transformation of domains into rank blocks;

figure 2 - dependence of decoding errors from errors in domain indices and conversion indices;

figure 3 - insertion of additional information into the basic fractal coding algorithm;

4 is a procedure for recording additional information.

Figure 1 shows the affine transformation of domains into rank blocks, which consists in fitting the selected domain domain to the processed rank using affine transformations.

Figure 2 shows the dependence of decoding errors on errors in domain indices and transform indices. Where can we conclude that the error in the conversion indices practically does not lead to distortions of the reconstructed image.

Figure 3 shows the insertion of additional information into the basic fractal coding algorithm. In the proposed method, the insertion of additional information is carried out when fitting a domain to a rank block. In this case, the insertion occurs in the digits that determine the index of turns, which is presented in figure 4. Since this data is not added in addition to the original signal, but replaces part of the original signal, the signal bandwidth does not increase by adding this information.

This method of transmitting additional information during fractal coding of images can be implemented on modern signal processing processors. The specified method can find its application in the transmission of additional information on low-speed communication channels. As additional information, hidden information, another image or another useful message can be used.

Information sources

1. Ulrich Schmidt, Digital Video Technology. Franzis Verlag, Feldkirchen, 1996.

2. Patent No. 2292662, IPC ⁸ H04N 7/08 of 01/27/2007

3. S. Welstead. Fractals and wavelets for compressing images in action. Tutorial. - M .: Triumph Publishing House, 2003 - 320 p.

Claims (1)

A method for transmitting additional information when encoding images, comprising the steps of a) digitizing the original image, b) compressing it using a fractal compression method, c) inserting additional information, d) decompressing the compressed image, e) extracting additional information, characterized in that when compressing the original image using the fractal compression method, a binary sequence of three digits representing additional information is recorded in the orientation indices of the domain blocks, then taking into account this additional information, the processed domain is rotated and the brightness coefficients a and contrast contrast s are searched for using the least squares method corresponding to the optimal values at which the expression is minimized:

where {d _ij } and {r _ij } are the pixel values of the domain and rank domains, as a result, they find the optimal domain taking into account the built-in additional information for encoding the rank block, after which the domain indices, brightness and contrast coefficients, transmit additional information by communication channel.

Images