Data Compression Lec#2-2018 Word

The primary types of redundancy can be found in image:
1. Coding: Coding redundancy occurs when the data used to represent the image not utilized in an optimal manner. For example, if we have an 8 bits/ pixel image that allows 256 gray- level value, but the actual image contains only 16 gray-level values, this is a suboptimal coding, where only 4 bits/pixel are actually needed.
2. Interpixel (Spatial Redundancy): Interpixel redundancy occurs because adjacent pixels tend to be highly correlated. This is a result of the fact that in most images the brightness levels do not change rapidly, but change gradually, so that adjacent pixel values tend to be relatively close to each other in value (for video, or motion images, this concept can be extended to include interframe redundancy, redundancy between frames of image data).
3. Psychovisual redundancy: refers to the fact that some information is more important to the human visual system than other types of information. For example, we can only perceive spatial frequencies below about 50 cycles per degree so that any higher-frequency information is of little interest to us.