geotiff vs ecw

[Frank Warmerdam]

Travis Kirstine GIS Tech wrote:
> In general do RGB ecw's with a compression of 20:1 outperform 8bit geotiff
> with overviews.

Travis,

I assume by "outperform" that you mean display faster?  I don't know the
answer, so I think you would really have to setup a test to know for sure.
But I would not be at all surprised to find the 8bit geotiff was faster.

If you use RGB imagery, are you using an RGB output format? (jpeg or png24)
If so, the re-compression of the mapview can take significantly longer than
compressing an 8bit paletted result in gif or png format.  If using an 8bit
output format then the resulting image quality can be pretty bad.
Approaches to alleviating that (error diffusion) will slow things down
a bunch more.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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