L4.Image Coding Flashcards
How does frequency-domain processing make encoding of images more efficient?
- transform image into freq-domain
- encode only features that can be perceived by Eye
- reverse transform at receiver
Step 1 of JPEG image compression
- image 640x480 RGB pixels
- convert each to Y and ((I,Q) or (U,V))
- reduce I,Q to 2 320x240 matrices (averaging 2x2)
- consider Y,I,Q divided in 8-bit tiles
Step 2 of JPEG image compression
- DCT2 to each 8x8 tile
- (Fx,Fy,DCT) with small high frequency components
Step 3 of JPEG image compression
- Quantize DCT coeffs with table
- > divide
- > round to int
Step 4 of JPEG image compression
Encode differences in DC-DC components between tiles
Step 5 of JPEG image compression
- zig zag
- sum successive 0s (run length code )
Is RGB ro YIQ better for processing?
YIQ
DIfference between JPEG, MPEG and ZIP compression?
Jpeg, Mpeg are lossy
By what factor doe Jpeg compress images?
10x
By what factor does Mpeg compress videos?
100x
What choise decides the quality/compression trade-off?
Choice of Coefficient quentization matrix
What process of compressing increases sensitivity to bi-errors?
Huffman coding
Where is huffman coding used?
image compression
MP3 music encoding
Disadvantage of Huffman codes?
Sensitivity to bit error
What happens when a huffman code is affected by a bit error?
Variable length means if on symbol is affected all the ones following it are fucked
