电子科发女学光电科学与工程学院 SCHOOL OF OPTOELECTRONIC SCIENCE AND ENGINEERING OF UESTC 4.Measuring Image Information Shannon's first theorem: n->oo ● Lave.is the average number of code symbols required to represent all n symbol groups. Lave.n can be made arbitrarily close to H by encoding infinitely long extensions of the single-symbol source
4. Measuring Image Information Shannon’s first theorem: , lim[ ] H avg n n L n Lavg,n is the average number of code symbols required to represent all n symbol groups. Lavg,n/n can be made arbitrarily close to H by encoding infinitely long extensions of the single-symbol source
电子科发女学光电科学与工程学院 SCHOOL OF OPTOELECTRONIC SCIENCE AND ENGINEERING OF UESTC 5.Fidelity Criteria o The error between two functions is given by: e(x,y)=f(x,y)-f(x,y) ● So.the total error between the two images is M-1N-1 ∑∑fx,y)-f(x,] x=0y=0 The root-mean-square error averaged over the whole image is 明
5. Fidelity Criteria 2 1 0 1 0 [ ( , ) ( , )] 1 [ ( , ) ( , )] ( , ) ( , ) ( , ) f x y f x y MN e f x y f x y e x y f x y f x y rms M x N y The error between two functions is given by: So, the total error between the two images is The root-mean-square error averaged over the whole image is
电子科发女学光电科学与工程学院 SCHOOL OF OPTOELECTRONIC SCIENCE AND ENGINEERING OF UESTC 5.Fidelity Criteria A closely related objective fidelity criterion is the mean square signal to noise ratio of the compressed-decompressed image M-1N-1 ∑∑fx,y SNRms x=0y=0 M-1N-1 ∑∑[f(xy)-f(x,y] x=01y=0
A closely related objective fidelity criterion is the mean square signal to noise ratio of the compressed-decompressed image 2 1 0 1 0 2 1 0 1 0 [ ( , ) ( , )] ( , ) f x y f x y f x y SNR M x N y M x N y ms 5. Fidelity Criteria
电子科发女学光电科学与工程学院 SCHOOL OF OPTOELECTRONIC SCIENCE AND ENGINEERING OF UESTC 5.Fidelity Criteria Value Rating Description TABLE 8.2 Rating scale of Excellent An image of extremely high quality,as good as you could the Television desire. Allocations Study 2 Fine An image of high quality.providing enjoyable viewing. Organization. Interference is not objectionable. (Frendendall and Passable An image of acceptable quality.Interference is not Behrend.) objectionable. Marginal An image of poor quality:you wish you could improve it. Interference is somewhat objectionable. Inferior A very poor image,but you could watch it.Objectionable interference is definitely present. 6 Unusable An image so bad that you could not watch it. ab c FIGURE 8.4 Three approximations of the image in Fig.8.1(a)
5. Fidelity Criteria
电子科发女学光电科学与工程学院 SCHOOL OF OPTOELECTRONIC SCIENCE AND ENGINEERING OF UESTC 6.Image Compression Models FIGURE 8.5 Functional block diagram of a general image compression system. f(x,y) or Mapper Symbol Quantizer f(x,y,t) coder Compressed data for storage Ecoder and transmission Symbol Inverse f(x.y) or decoder mapper f(x,y,t) Decoder
6. Image Compression Models