[OSGeo-Discuss] 'lossless' JPEG2000

[Christopher Schmidt]

On Mon, Feb 25, 2008 at 09:26:16PM -0500, Ed McNierney wrote:
> Christopher -
> 
> Let me add the "evidence" that I have found that reducing the strip size
> in LZW-compressed GeoTIFFs has, not surprisingly, a VERY large effect on
> read performance - about a factor of 10 in the particular cases I used.
> That indicates that the data you report might not be a good 'order of
> magnitude' measure of performance.  I'm not talking about "subtler"
> effects of memory, caching, etc. but the substantial effect of changing
> the LZW strip size in a large image; the amount of work required to
> decompress a portion of that image is very, very different from the case
> in which the entire file is treated as one strip, due to the
> dictionary-building nature of the LZW algorithm.

Interesting, I didn't realize that the differences we were discussing
were so large. Given that, perhaps I need to reevaluate: My knowledge of
image compression is very poor (especially compared to yours!) and
you're right in saying that it is poor practice to pass off my numbers
without having fully understood them!

Thanks for the feedback: now I'll just have to go read a bunch more on
how to actually get better results, since clearly I haven't taken your
feedback thus far as seriously as I should!

Regards,
-- 
Christopher Schmidt
Web Developer