04-12-2012, 01:26 PM
JPEG Compression
JPEG Compression.ppt (Size: 535 KB / Downloads: 38)
Fact about JPEG Compression
JPEG stands for Joint Photographic Experts Group
JPEG compression is used with .jpg and can be embedded in .tiff and .eps files.
Used on 24-bit color files.
Works well on photographic images.
Although it is a lossy compression technique, it yields an excellent quality image with high compression rates.
Steps in JPEG Compression
1. (Optionally) If the color is represented in RGB mode, translate it to YUV.
2. Divide the file into 8 X 8 blocks.
3. Transform the pixel information from the spatial domain to the frequency domain with the Discrete Cosine Transform.
4. Quantize the resulting values by dividing each coefficient by an integer value and rounding off to the nearest integer.
5. Look at the resulting coefficients in a zigzag order. Do a run-length encoding of the coefficients ordered in this manner. Follow by Huffman coding.
Converting RGB to YUV
YUV color mode stores color in terms of its luminance (brightness) and chrominance (hue).
The human eye is less sensitive to chrominance than luminance.
YUV is not required for JPEG compression, but it gives a better compression rate.
Discrete Cosine Transform
The DCT transforms the data from the spatial domain to the frequency domain.
The spatial domain shows the amplitude of the color as you move through space
The frequency domain shows how quickly the amplitude of the color is changing from one pixel to the next in an image file.