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Image coding method

An image coding and image technology, applied in the field of image coding, can solve problems such as improving compression efficiency

Active Publication Date: 2015-09-09
PEKING UNIV
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

On the other hand, the human eye has different sensitivity to distortion in different image contents, but traditional image compression uses the same quantization method for all regions of the image, which limits the improvement of compression efficiency

Method used

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Embodiment 1

[0033] A method for making image coding, comprising the steps of,

[0034] Step 1) carry out DCT transformation to several image blocks;

[0035] Step 2) counting the distortion and code rate of each frequency band coefficient of the several image blocks under different quantization step sizes;

[0036] Step 3) select the mean value of the opposite number of the distortion corresponding to the rate of change of the code rate not exceeding the quantization step size of the maximum distortion as the Lagrangian factor in the rate-distortion optimization;

[0037] Step 4) Obtain the quantization table by calculation and perform quantization;

[0038] Step 5) During the quantization process, the coefficients are adaptively shrunk based on human visual characteristics to obtain a compressed image.

Embodiment 2

[0040] A method for making an image encoding, which includes the same steps as in Embodiment 1; the difference is that step 2) also includes, calculating the corresponding quantization coefficient in each frequency band when the quantization step Qstep is minQ to maxQ (wherein minQ<maxQ) Distortion, where the quantization step size is an integer, the probability distribution of quantization coefficients in each frequency band in all blocks is counted, and the entropy of quantization coefficients is used to estimate the code rate of JPEG encoding.

Embodiment 3

[0042] A kind of making image encoding method, the step that it comprises is identical with embodiment 2; Difference is to calculate the Lagrangian factor of each frequency band under different quantization steps according to formula (1), λ i,j (Qstep);

[0043] λ i , j ( Qstep ) = D i , j ( Qstep + 1 ) - D i , j ( Qstep ) R i , ...

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Abstract

The embodiment of the invention discloses an image coding method, comprising the steps as follows: coding an image via a quantization table computing method optimized by rate-distortion and a region adaptive coefficient contraction method based on a human visual system. The image coding method of the invention could be used for coding the image via the quantization table computing method optimized by rate-distortion and the region adaptive coefficient contraction method based on the human visual system so as to reduce size of an image file under the condition that the subject quality of compression images is the same.

Description

technical field [0001] The invention relates to the technical field of digital signal processing, in particular to an image coding method. Background technique [0002] Image compression is the basis for ensuring the effective application of images. JPEG (Joint Photographic Experts Group) is the first international image compression standard formulated under the leadership of the International Organization for Standardization (ISO). Due to the excellent quality of JPEG, it has achieved success in just a few years and has been widely used in the Internet and digital camera fields. 80% of the images on the website use the JPEG compression standard. [0003] Quantization is an effective means to reduce human visual redundancy in the process of compression. Therefore, according to the characteristics of image content, selecting an appropriate quantization table can improve image compression efficiency. On the other hand, the human eye has different sensitivity to distortion in ...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H04N19/625H04N19/124H04N19/147
Inventor 马思伟张新峰王诗淇
Owner PEKING UNIV
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