[gdal-dev] Question on image formats vs performance and quality

[Armin Burger]

Steve

ECW needs Byte data *per band*, so you could convert 3 Band RGB (every 
band in byte) data without problems into ECW.

Performance is another issue. As long as you do not have problems with 
disk space I would recommend continuing to use uncompressed Tiff with 
overviews. In combination with Mapserver/Gdal the best solution 
regarding performance. In our tests most of the time ~ 1.5 to 2 times 
faster than ECW, and becoming worse for ECW for more concurrent users.

And I think the current ECW license conditions also have issues for 
serving this format.

Other formats like Erdas Imagine are not faster than Tiff and with the 
BigTiff library also Tiff files can become > 4GB.

Reagrds,
Armin

On 22/03/2009 05:49, Stephen Woodbridge wrote:
> Hi all,
> 
> I would be interest in you thoughts on comparing MrSID, ECW, and Tiff 
> images from the perspective of image quality and performance.
> 
> The scenario is I have imagery in MrSID. I typically decompress that 
> into Tiled Tiff uncompressed imagery with overviews. I server it via 
> mapserver and it has reasonable performance.
> 
> I have not considered serving it from the MrSID files because I don't 
> have a license to compress the files and I would need to reproject them. 
> Also I'm guessing it in not a good idea to uncompress and compress them 
> again as it is lossy and the image degrades.
> 
> I have never worked with ECW, but I'm concerned about:
> 1) ECW is 8-bit data only and the source data is 24 bit RGB data
> 2) how does it compare performance wise to say the tiff images when 
> rendering?
> 
> Are there other formats that would be good to consider? What are their 
> characteristics?
> 
> Thanks,
>   -Steve
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