{ Lossy Compression William Dayton Nick Trojanowski
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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
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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
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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
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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
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)
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Group of functions that express a signal in sum of different
sinusoids 8 types DCT-II most common Discrete Cosine Transform
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Audio Compression Higher quantization at extreme ranges 10:1
compression ratio almost indistinguishable from original Less
accuracy after loud sections Bad compression around 3kHz
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
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MP3 vs WAV Can you hear the difference?
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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
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
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The one on the right has over triple the bitrate of the one on
the left.