MTD2 class 13
2. Video Compression 3. Compression in Premiere 4. Continue work on Animation
JPEG determines for an image is turned into a byte stream. Converts from RBG to YCbCr JPEG
- lossy image compression
- lossless image compression
critical and ancillary. ancillary chunks are used to extend png capabilities while maintaining compatibility with older versions. Ancillary chunks my safely ignored.
PNG is also paren free and based on open source library libpng Discrete cosine transform
Temporal Redundancy (inter-frame)- successive frames contain the same information
Spatial Redundancy (intra-frame)- redundancy within a single frame
MPEG2 Three way on encoding a frame
(P)forward predictive frames
(B)bidirectional predictive frames
I frames contain a full compressed images of the frame (Spatial). P frames contain predictive information to help remove Temporal redundancy. Frames are compared through time and through a process called "motion compensation" a motion vector map is created and only the differences between frames is coded. P frames only work in the forward direction. B frames are encoded against the next and previous frames and work in both directions. P and B frames are usually 90%-98% smaller than I frames.
These frames are arranged into a GOP (group of pictures). There are many possible structures for each GOP a common 15 frame GOP could be structures like
Continue work on flash animation