Redundancy can be broadly classified into Statistical redundancy and psych visual redundancy.

• Statistical redundancy can be classified into inter-pixel redundancy and coding redundancy.
• Inter-pixel can be further classified into Spatial redundancy and Temporal redundancy.
• Spatial redundancy or correlation between neighboring pixel values.
• Spectral redundancy or correlation between different color planes or spectral bands.
• Temporal redundancy or correlation between adjacent frames in a sequence of images in video applications.
• Image compression research aims at reducing the number of bits needed to represent an image by removing the spatial and spectral redundancies as much as possible.

• In digital image compression, three basic data redundancies can be identified and exploited: Coding redundancy, Inter-pixel redundancy and Psych visual redundancy.

• Coding Redundancy:

  • Coding redundancy is associated with the representation of information.
  • The information is represented in the form of codes.
  • If the gray level of an image is coded in a way that uses more code symbols than absolutely necessary to represent each gray level then the resulting image is said to contain coding redundancy.

• Inter-pixel Spatial Redundancy:

  • Interpixel redundancy is due to the correlation between the neighboring pixels in an image.
  • That means neighboring pixels are not statically independent. The gray levels are not equally probable.
  • The value of any given pixel can be predicated from the value of its neighbors that is they are highly correlated.
  • The information carried by individual pixel is relatively small. To reduce the interpixel redundancy the difference between adjacent pixels can be used to represent an image.

• Inter-pixel Temporal Redundancy:

  • Interpixel temporal redundancy is the statistical correlation between pixels from successive frames in video sequence.
  • Temporal redundancy is also called interframe redundancy. Temporal redundancy can be exploited using motion compensated predictive coding.
  • Removing a large amount of redundancy leads to efficient video compression.

• Psychovisual Redundancy:

  • The Psychovisual redundancies exist because human perception does not involve quantitative analysis of every pixel or luminance value in the image.
  • It’s elimination is real visual information is possible only because the information itself is not essential for normal visual processing.