Chapter 8
Digital Image Compression Techniques
1. Gray level JPEG Coding Performance
The performance of JPEG baseline coding algorithm for coding gray level Lena image (512x512)
is shown in Fig. 8cd.1. It is shown that even at 0.56 bits per pixel (corresponding to a compression
ratio of 14:1), the reconstructed image quality is very good. However, at a bit rate lower than 0.2
bits per pixel (compression ratio greater than 40:1), the quality degrades rapidly.
(a)
(b)
(c)
(d)
(e)
(f)
Figure 8cd.1. Reconstructed images from JPEG Bitstream at different bitrates. (a) original, (b) 0.90,
(c) 0.56, (d) 0.37, (e) 0.25, (f) 0.13
2. Color JPEG Coding Performance
The coding performance for color Lena image is shown in Fig. 8cd.2. It is observed that at 0.53
bpp (compression ratio of 45:1), the reconstructed image quality is very good. Note that a higher
compression ratio can be achieved for color image (compared to gray level image) since the
sensitivity of the chrominance components is small for the HVS.
(a)
(b)
(d)
(c)
(e)
Figure 8cd.2. Reconstructed images from JPEG Bitstream at different bitrates. (a) original, (b) 0.95, (c)
0.53, (d) 0.36, (e) 0.18 bits per pixel.
3. Gray level JPEG2000 Coding Performance
The coding performance of JPEG2000 algorithm (using JASPER software) corresponding to
Lena image is shown in Fig. 8cd.3. The coding has been performed with six levels of wavelet
decomposition, a code-block size of 64x64, a precinct size of 512x512, and one quality layer. It is
observed that the reconstructed image quality is good even at a compression ratio of 60:1.
(a)
(b)
(c)
(d)
(e)
Figure 8cd.3. Reconstructed images from JPEG2000 Bitstream at different bitrates. (a) 0.90, (b)
0.56, (c) 0.37, (d) 0.25, (e) 0.13
4. Color JPEG2000 Coding Performance
The coding performance of JPEG2000 algorithm (using JASPER software) corresponding to
color Lena image is shown in Fig. 8cd.3. The coding has been performed with six levels of wavelet
decomposition, a code-block size of 64x64, a precinct size of 512x512, and one quality layer. It is
observed that the reconstructed image quality is good even at a compression ratio of 133:1
(24/0.18=133)
(a)
(b)
(c)
(d)
Figure 8.22. Reconstructed images from JPEG2000 Bitstream at different
bitrates. (a) 0.95, (b) 0.53, (c) 0.36, (d) 0.18 bits/pixel.