Summary of the JPEG bitstream

Figure 7.12 and the above JPEG components have described how compression is achieved at several stages. Let us conclude by summarising the overall compression process:

• A "Frame" is a picture, a "scan" is a pass through the pixels (e.g., the red component), a "segment" is a group of blocks, a "block" is an 8x8 group of pixels.

• Frame header: sample precision (width, height) of image number of components unique ID (for each component) horizontal/vertical sampling factors (for each component) quantization table to use (for each component)

• Scan header Number of components in scan component ID (for each component) Huffman table for each component (for each component)

• Misc. (can occur between headers) Quantization tables Huffman Tables Arithmetic Coding Tables Comments Application Data