JPEG 2000
AS COMPLICATED AS "MEH" CAN GET
Presentation by Jesse Weaver
STARTING POINT
JPEG is a good compression format, especially for
photographic images
It has problems, however, including many ugly kinds of
artifacts at low file sizes
PROBLEMS WITH JPEG
There are three major kinds of artifacts
Colorspace artifacts occur from conversion to Y'CBCR
Ringing artifacts occur from quantization of DCT
coefficients
Blocking artifacts occur from the 8x8 blocking of the
compression
WAVELETS TO THE RESCUE
Many problems seem to occur because of the very localized
nature of blocked DCT
Wavelets have many of the same properties as DCTs (can
threshold coefficients, etc. while preserving image) but use
information from entire image at several scales
HAVE WE BEEN RESCUED?
HAVE WE BEEN RESCUED?
COMPLEXITIES...
We pay for the increase in image quality with a very
complex standard
First off, talking about a JPEG-2000 image is a bit like talking
about an MPEG movie; the image standard is technically JP2
Once we've selected JP2, however, far more options
present themselves
This can be seen in implementations of the standard (~1600
vs ~16000 for JasPer's JPEG and JP2 implementations)
COMPLEXITIES...
Every single option in JP2 can be twisted, rearranged and
modified
JP2 can be lossy or lossless, and encoded in several
different orders
The image is broken down into components; tiles, precincts,
then code-blocks; and also several different layers of
varying resolution, all of which have configurable sizes and
ordering
ENCODING FLOW
Once the wavelet-transformed image has been broken
down all the way into code blocks, it is then output in order
from most-significant to least-significant bit
This means that, in theory, a JP2 image can be progressively
sent and will gradually increase in quality
MY ENCODER
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QUESTIONS?