Patent ID: 8655092
Filing Date: 2014-02-18
Classification: H04N

Abstract:
1. A wavelet coefficient quantization method using a human visual model in image compression, comprising: Step 1: performing wavelet transform on an image to be compressed, and partitioning all obtained sub-bands into n×n blocks, and marking each block by B(j,d,i), wherein j represents a wavelet transform level of the sub-band where the block is located, d represents a direction of the sub-band where the block is located, and i represents a position of the block in the sub-band; Step 2: calculating a maximal value MAX calculating a luminance component T wherein a is a voltage when a pixel value of a Cathode Ray Tube (CRT) display is 0, b is a scale factor between a pixel value and a voltage value, c is a gamma value of the display, w is the Weber ratio, g is an energy gain factor at the k Step 3: respectively obtaining blocks of HL and LH sub-bands of the image to be compressed after the second and third levels of wavelet transform, and calculating a masking component T wherein C(2,HL,i) represents a maximal value of absolute values of coefficients in a block B(2,HL,i), C(3,HL,i) represents a maximal value of absolute values of coefficients in a block B(3,HL,i), C(2,LH,i) represents a maximal value of absolute values of coefficients in a block B(2,LH,i), and C(3,LH,i) represents a maximal value of absolute values of coefficients in a block B(3,LH,i); Step 4: calculating a joint component T wherein α and β respectively represent luminance component and masking component weight values; Step 5: quantizing the obtained joint component T Step 6: selecting multiple test images of the same size as the image to be compressed, using the wavelet transform method to obtain wavelet coefficients, and calculating a frequency component of the visual model for each an respectively in the following manner: adjusting a quantized value to quantize the band until distortion of a recovered image is just perceptible to human eyes, recording the current quantized value as a frequency Just Noticeable Differences (JND) value of the image at the band, and averaging the frequency JND values of the same bands in the multiple images to obtain a frequency component T Step 7: using the obtained quantized value Q(j,d,i) of the joint component T wherein γ represents a frequency component weight value; and Step 8: performing quantization using the visual quantization threshold.