Image and Video Image and Video CompressionCompression

Communication SystemsCommunication Systems

EECE 453EECE 453

Hassan MansourHassan Mansour

Image CompressionImage Compression

Most popular techniques:Most popular techniques: Color subsamplingColor subsampling Transform Coding (JPEG, JPEG2000,…)Transform Coding (JPEG, JPEG2000,…) Fractal CodingFractal Coding

Available Compression standards:Available Compression standards: JPEG, JPEG2000, JPEG-LS, JBIG, JBIG2 JPEG, JPEG2000, JPEG-LS, JBIG, JBIG2

(ISO)(ISO) GIF, PNG, TIFF, BMP, WMP,…GIF, PNG, TIFF, BMP, WMP,…

JPEG compressionJPEG compression

DCT(x-128)

QuantizationJPEG

file

Entropy Coding

Zig-Zag Scan

JPEG quality per compression JPEG quality per compression ratioratio

Original Compressed to 12%

Compressed to 6% Compressed to 2%

Video Compression (MPEG)Video Compression (MPEG) Started with MPEG-1/H.261 (1991, video Started with MPEG-1/H.261 (1991, video

CD)CD) MPEG-2 was launched in 1994 and MPEG-2 was launched in 1994 and

became the standard for DVDs.became the standard for DVDs. Finally, MPEG-4 was introduced in 1998.Finally, MPEG-4 was introduced in 1998.

MPEG-4 ISO is based on H.263MPEG-4 ISO is based on H.263 MPEG-4/AVC is the new H.264 standard used MPEG-4/AVC is the new H.264 standard used

in HD-DVD and Blu-ray Disc.in HD-DVD and Blu-ray Disc. Both MPEG-4 ISO and H.264/AVC are used for Both MPEG-4 ISO and H.264/AVC are used for

mobile video.mobile video.

Basic Compression Basic Compression AlgorithmAlgorithmPicture N Picture

N+1Difference

-Encode picture N as JPEG

-Perform Motion Estimation/Compensation on picture N+1 using picture N

-Encode the difference as JPEG

Motion Estimation / Compensation :

Decoding exampleDecoding example

+

Residual

Signal

Motion-

Compensated

Decoded

Signal

Video Compression Video Compression ReferenceReference

http://mia.ece.uic.edu/~papers/http://mia.ece.uic.edu/~papers/WWW/MultimediaStandards/WWW/MultimediaStandards/chapter7.pdfchapter7.pdf