[gdal-dev] Re: JPEG2000 question

[Jukka Rahkonen]

Todd Smith <smith.todd <at> gmail.com> writes:


> - In and out of GDAL, compare the performance of the different JPEG2000
libraries against each other. Which can decompress/compress the fastest? I don't
have to worry about moving any of the data over a network during
compression/decompression, so all I'm really asking is, if I have a big beefy
machine, which library will process the data the fastest?

To give a somewhat reliable answer to your question would mean a lot of planning
and hard, controlled work. I hope somebody will do it some day and report it.
While JPEG and ECW have mainly one user selectable parameter, compression
quality, JPEG2000 is an extraordinary complicated format because of the huge
amount of options it has. Therefore your question should be formatted as 

"Which can decompress/compress the fastest an image with these parameters:
Big Image Tiled (2bpp) 13,333x13,333 (full RGB) 1024x1024 tiles, RPCL, W9x7,
Clayers=5, Clevels=6, Cblk={64,64}, Cprecincts={256,256}"

Parameters are copied from these online documents:
http://www.kakadusoftware.com/documents/kakadu-encode-speed.pdf
http://www.kakadusoftware.com/documents/kakadu-decode-speed.pdf
 
> - What about plain old ECW vs JPEG2000 (.ecw vs .jp2)? Again, which performs
faster for compression/decompression?

ECW vs which kind of JPEG2000? However, ecw is rather standard and we can guess
that the late ERMapper was aiming to rather similar result with its own JPEG2000
compressor. I have an "ECW JPEG 2000 Compressor 7.0" from the ER Mapper time on
my machine and it is faster with ECW than with JPEG2000. Still I can only say
that ER Mapper ECW is faster that ER Mapper JPEG2000. I have a feeling that
Kakadu JPEG2000 is faster than ER Mapper JPEG2000 but I cannot run ER Mapper
JPEG2000 with my favourite Kakadu parameters.

> - As we investigate alternatives to JPEG and ZLIB compression (because we like
the compression sizes we get with jpeg, but we like the quality of zlib, and
yeah I know I'm comparing lossy vs. lossless so it's not a fair comparison
but...) what other compression formats would any of you recommend that offer at
least a 6 to 1 compression ratio, but also process very quickly (inside and
outside of GDAL).

There are for sure other fine JPEG2000 utilities around, but I know best the
free demo programs from Kakadu. Have a try by compressing some reasonable sized
test image, 500 MB or so, to lossless JPEG2000 with kdu_compress and open it
with kdu_show viewer. This test should give some idea about the speed of
compressing and browsing JPEG2000 imagery when done properly. Reading the
Usage_Examples.txt file and checking all the options supported by kdu_compress
will affirm that JPEG200 really is a complicated beast.

By the way, we compress aerial images (1000 by 10000 pixels) for archive with
these parameters, they should be quite good for interactive viewing and serving
through JPIP as well. Result is lossless, naturally.

-rate - Clevels=7 Clayers=27 Creversible=yes Cycc=yes
Cprecincts={256,256},{128,128} Corder=RPCL Cblk={32,32} ORGgen_plt=yes
ORGtparts=R ORGgen_tlm=8 -cpu 0 -mem

-Jukka Rahkonen-