JPEG
<p>Dec 02, 2012 08:16 PM
 
LOSSY comprehension of images.
 
adjustable compression... typical is 1 to 10 with little perception loss.
 
most common format on WWW.
 
max image size of 64k by 64k.
 
typical use:  photos and paiting sof realistic scenes with smooth variations.
 
most common for cameras.
 
jpeg not suited for line drawings... textual or iconic graphics.
 
JPEG compression:  
 
ENCODING:  see DCT  Discrete Cosine Transform  and see
 8 by 8 block of  wavelets....  it  makes a combo of these.
 
note: it is diag symmetric.   red checkerboard...
 
Quantization:  human eye is good at seeing small diffs in brightness over a large area but not
a high freq brightness variation.....  SO, can greatly reduce info in high freq compts.
 
so, just divide each compot in the freq domain by a constant
and round it off...  this is the ONLY lossy oper in the whole DCT.
 
see Photos of JPEGS at end... of varying quality
(bb:  could be that highly eccentric parts of a visual image  (peripheral/ non foveated;
are simply  highly compressed versions of the image... useful for foveation direction).
 
 
 
 
 
 
 
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