Image compression method with variable quantization parameter

An image compression method with a variable quantization parameter, for processing a plurality of pixels of an image, the method comprising:

• receiving N successive pixels;
• obtaining N pixel differences and N map differences corresponding to the N pixels according to values of the N pixels through a differential pulse code modulation (DPCM) means, wherein the DPCM means comprises:
• obtaining the N pixel differences respectively corresponding to the N pixels according to the values of the N pixels;
• and
• performing a mapping means on the N pixel differences respectively, so as to obtain the N map differences respectively corresponding to the N pixel differences, wherein the mapping means further comprises:
• when the ith pixel difference di in the N pixel differences is greater than or equal to 0, obtaining the corresponding ith map difference ni by multiplying the pixel difference di by 2, where 0<=i<N;
• and when the ith pixel difference di in the N pixel differences is smaller than 0, obtaining the corresponding ith map difference ni by subtracting 1 from a result obtained by multiplying the pixel difference di by 2;
• calculating to obtain a quantization reference value corresponding to the N pixels according to the N pixel differences;
• obtaining a quantization parameter corresponding to the N pixels according to the quantization reference value;
• and
• encoding the N map differences according to the quantization parameter.