wk 8.2

Question 1

what is huffman coding

Answer 1

fixed-length code (8 bits) -> variable length code

to represent the pixel values in an image

Question 2

effect of huffman coding

Answer 2

more frequent pixel values will be assigned shorter-length bits

Question 3

Common methods of lossy compression

Answer 3

• (JPEG) Joint Photographic Experts Group
• (MPEG) Moving Picture Experts Group / video
• Wavelets

Question 4

can the compressed image be recovered

Answer 4

Only an approximation of the original image can be recovered, lower quality, but smaller

Question 5

JPEG Encoding

Answer 5

• Discrete Cosine Transform (DCT)
• DCT: reversible transform & retains all the information
• JPEG and MPEG is obtained by discarding some of DCT components

Question 6

phases of JPEG

Answer 6

blocked image -> DCT -> Quantisation -> Lossless compression -> compressed image

Question 7

steps to JPEG Compression

Answer 7

blocked image -> divided into 8x8 pixel blocks, transformed and compressed
DCT -> applied to each block
Quantisation -> to reduce number of bits needed for encoding
Lossless compression -> RLE & Huffman Coding
compressed image