Sattelite Image Data Compression using Vector Quantization on Wavelet Information

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Sattelite Image Data Compression using Vector Quantization on Wavelet Information

(3) Image Compression using Vector Quantization on Wavelet Informations
Firstly, the wavelet decomposition is applied to the original image and results wavelet sub band images. These sub band images are coding by vector Quantization using each sub band's codebooks. These codebooks are called mutiresolution codebooks. Fig. 2 (a) shows the image compression and Fig. 2(b) shows the image decomposition. The principle method of this technique is bit assignment for each sub band besed on the energy in that sub band. The higher energy sub band is encoded by using higher bit rate.

(a) Image Compression

(b) Image decompression
Figure 2 Image compression and decompression using VQ on wavelet informations
The application of vector Quantization on wavelet information is an image compression technique introduced by [7]. For the traditional method of bit assignment is shows in Fig. 3. By using this technique, the sub band HH is discarded. This causes the image loses some details. Thus, a new scheme of bit assignment in Fig.4 is proposed to maintain the edges of image.

LLLL	LLHL	HL
LLLH	LLHH	HL
LH		HH

(a) Subband images

8 bpp	VQ 2 bpp Codebook size=2*2 N=256	VQ 0.5 bpp Codebook size=4*4 N=256
VQ 2 bpp Codebook size=2*2 N=256	VQ 0.5bpp Codebook size=4*4 N=256	VQ 0.5 bpp Codebook size=4*4 N=256
VQ 0.5bpp Codebook size=4*4 N=256		0 bpp

(b) Bit assignment

Fig. 3 Traditional method at bit rate = 1.03125 bpp

LLLL	LLHL	HLLL	HLHL
LLLH	LLHH	HLLH	HLHH
LHLL	LHHL	HHLL	HHHH
LHLH	LHHH	HHLH	HHHH

(a) Subband images

8 bpp	VQ 2 bpp Codebook size=2*2 N=256	VQ 0.5bpp Codebook size=4*4 N=256	VQ 0.5bpp Codebook size=4*4 N=256
VQ 2bpp Codebook size=2*2 N=256	VQ 0.5bpp Codebook size=4*4 N=256	0 bpp	VQ 0.5bpp Codebook size=4*4 N=256
VQ 0.5bpp Codebook size=4*4 N=256	0 bpp	0 bpp	VQ 0.25bpp Codebook size=4*4 N=16
VQ 0.5bpp Codebook size=4*4 N=256	VQ 0.5bpp Codebook size=4*4 N=256	VQ 0.25bpp Codebook size=4*4 N=16	VQ 0.5bpp Codebook size=4*4 N=256

(b) Bit assignment

Fig. 4 Proposed method at bit rate = 1.03125 bpp

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