[mapserver-dev] Maps for 16 bit displays

[Ian Walberg]

Thomas,

While creating image files in the 565 format would be ideal this is not required.

What we do need is to be able to create images that look good when displayed using a video card in 16 bit colour depth. As you suggest we are looking at reducing/dithering the images from 24 bit to 16 bit when displayed but of course if we can reduce the colour range wen rendered this would most likely make the image quality better.

Thanks

Ian

-----Original Message-----
From: thomas bonfort [mailto:thomas.bonfort at gmail.com] 
Sent: Monday, June 11, 2012 8:22 AM
To: Ian Walberg
Cc: mapserver-users at lists.osgeo.org; mapserver-dev at lists.osgeo.org
Subject: Re: [mapserver-dev] Maps for 16 bit displays

Ian,
I don't believe it is currently possible to render 16bit images.
However, I'm pretty certain PNG does not support 565 encoding, and couldn't find any reference as to whether jpeg can either. Unless you are accessing the image bytes directly from the mapserver library (which I suspect you are not, it is not a public api/structure), I would investigate in reducing from 32 to 16 bits directly on the device at image loading time.

If you absolutely need 565 encoded output, I suspect the code can be worked on on the vector side with AGG to produce that, but it will not be a trivial task. Concerning raster rendering, this would also be a non trivial task.

regards,
thomas

On Fri, Jun 1, 2012 at 11:27 PM, Ian Walberg <ian.walberg at airborne.aero> wrote:
> Hello folks,
>
> We need to render maps for a system which has a 16 bit colour (yes I 
> am
> English) depth.
>
> Currently we render the images at 24 bit (888) and they look fabulous.
>
> However when they are rendered on the target hardware they are crudely 
> reduced to (565) and this causes some horrible artefacts and banding.
> Our best guess is that the lower bits are just being discarded.
>
> So now we understand the problem the question is what we can do to 
> generate the map images with a reduce RGB range so that they are 
> displayed correctly.
>
> Having a look at the various options we cannot see anything between 
> 256 colour and 24 bit colour which would help.
>
> Anyone have any good ideas?
>
> Thanks
>
> Ian
>
>
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