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Video Compression
Bee Fong
Lossy Compression
 Inter

Compression among frames
 Intra

Frame Compression
Frame Compression
Compression in a frame
Intra Frame Compression
 Similar

to Image Compression
Do not discussion, please refer to the image
compression section (JPEG)
Coding Order != Display Order
 Figure
1
 Figure 2
Encoding rate may be slow, but Decoding
rate is fast
Inter Frame Compression
I
Frame

P

B

D
Intra Frame
Frame
Predictive Frame
Frame
Bidirectional Frame
Frame
Compression Methods
 Subsampling

Duplicate frames, 1 compression stream
 Differencing

Compare a Frame with its predecessor. Take
the difference.
 Block

Differencing
Frame divided into blocks, compare block
difference.
Compression Methods
 Motion

Motion vector, compare blocks with location
difference.
 Frame

Compensation
Segmentation
Frame divided into equal-size nonoverlapping
blocks, block size affecting the chance of
matching
 Search

Threshold
Compare #difference with a predefined value
Compression Methods
 Block

Search
Search area = (width + 2dx)(height + 2dy)
 Distortion

Measure
Use Pel difference instead of mean absolute
difference
Compression Methods
 Suboptimal

Do some search in the search area, not all.
 Coding


Motion Vector
Use prediction motion vector
Grouping motion vectors
 Image

Search Methods
Objects
Use overlapping object layers
My Ideas
 “Cutting-Sandwich
Compression”
 Motivation: for high quality compression,
or lossless video compression 
compression rate is low.
Cutting-Sandwich Compression
 Cutting
Frames horizontally or vertically,
then do compression
 Reason: for a single frame, the repeating
rate of pixels is low
 Assumption: the repeating chance of the
same line of frames may be higher.
Implementation
 Base
on the general Video compression
approach, treat images in another
dimensions (horizontal cutting images, or
vertical cutting images)
 Treat as a 3-d block of frames, stored in
buffer for encoding / decoding.
Implementation
 For
each 3-d block, compare the general,
horizontal and vertical compression rate,
take the best.
 Add two extra bits for mode selection.

00 for general mode, 01 for vertical mode, 10
for horizontal mode and 11 for open.
 Tradeoff
is low.
Tradeoff
 For
example, 1 block = 640 frames of (640
x 480) image, 3 bits per pixel.
 2 extra bits / (640 x 640 x 480 x 3) bits ~=
0%.
Tradeoff
 More
resources are needed for the
compression (time, software, hardware)
 Encoding rate may be slower, Decoding
rate – no big difference if we take some
buffer (again, only decoding needed to be
fast in general case)
 Software and hardware are cheap now,
not a technical problem.
Tradeoff
 Buffer
is needed for encoding and
decoding in video compression, not a big
deal.
Other supportive compression
methods in Sandwich
 Run-Length
 LZ77
 LZW
Encoding