[mapserver-users] Mapserver 3.7 and GD2 support

[Frank Warmerdam]

woodbri at swoodbridge.com wrote:
> So this raises a question for me. Adding GD 2 gives mapserver the 
> ability to deal with more colors internally, but web browsers still 
> are limited on the number of colors they can use!
> 
> So what happens?
> 
> I am assuming the mapserver can build a high color memory image of 
> the map in question, but then it still has to reduce it to around 256 
> colors on output. Do we get better output images because it can defer 
> the color reduction until it knows all the colors it needs to deal 
> with? or does it output higher color images and the browsers can 
> actually handle more colors than I think? or something else?
> 
> Inquiring minds want to know!!

Stephen,

When operating in 24bit mode with MapServer 3.7 and GD2 the actual png file
returned by MapServer is 24bit, and the reduction to less colors (if required)
would be done by the web browser.  However, most people are operating in at
least 16bit color depth these days, and reduction from 24bit to 16bit is
barely visibly noticable.

The real cost is in transporting the bulkier 24bit pngs back to the client.
For imagery applications returning JPEGs is more appropriate though they will
corrupt linework and text.

Best regards,

-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent