2. { Lossy Compression William Dayton Nick Trojanowski

3.  Lossy file compression compresses files by trimming out data, and therefore quality, from the original data.  The loss of data is not usually enough to be noticeable by the user, but can immensely save on file size. Definition

4.  Lossy compression loses data; lossless does not  When encoding data, lossy takes up less file space  Lossless compression – 9/10 original size  Lossy compression – 1/10 original size Lossy vs Lossless

5.  Transform Codecs  Samples taken, separated, quantized, and entropy encoded  Predictive Codecs  Data based off preceding data, by doing next byte based off previous Lossy Compression Types

6.   chroma filtering   4:2:2 means every 4 pixels are 4 luminance samples (Y), and 2 chrominance samples (RGB)   4:2:2 reduces by 33%, 4:1:1 & 4:2:0 by 50%   hue change not typically seen, can affect certain effects   YXbXr; Y = (R+B+G)/3, Xb = Y-B, Xr = Y-r 4:2:2 4:1:1 4:2:0 Image Compression

7.  File Types  JPEG  DjVu – AT&T Research Labs  PGF (Progressive Graphics File)  BTC (Block Truncation Coding) Image Compression cont.

8.  Best known image compression type, mostly commonly used on Internet  Used for digital photography  Based on discrete cosine transform (DCT)  Has varying compression ratios  First converted to YCbCr  Chroma downsampling to RGB  DCT Joint Photographic Experts Group (JPEG)

10.  Group of functions that express a signal in sum of different sinusoids  8 types  DCT-II most common Discrete Cosine Transform

11. Audio Compression  Higher quantization at extreme ranges  10:1 compression ratio almost indistinguishable from original  Less accuracy after loud sections  Bad compression around 3kHz

12. Audio Compression cont.  File Types  Opus  MP2  MP3  MP4  OGG  WMA  Musepack

13.  Uses psychoacoustics  Based on Musicam format  Sub-band coding  Ex: 128kbit/s  1/11 file size  Can use variable bit rate for encoding .mp4 can also do video MP2, 3, & 4

14. MP3 vs WAV  Can you hear the difference?

17. Video Compression  Mix between audio & image compression  Compression ratio between 10:1/200:1  Reduces redundancy & framerate  Bases image on macroblocks  No standard uncompressed format

18.  File Types  Motion JPEG  MPEG1  MPEG2  MPEG4  OGG Video Compression cont.

19.  MPEG is flexible & error resilient  Max bitrate for MPEG4 is 8000kbits/s  Achieves compression ratio 20:1 to 200:1  OGG is open source  Does audio, video, & text  Theora, Tarkin, Dirac for video  Theora made as competitor to MPEG4 MPEG1, 2, 4, & OGG

20. The one on the right has over triple the bitrate of the one on the left.