forced palette for RGBA images

[Steve Lime]

Thomas, these are great additions. I'm looking forward to using them myself as I'm dealing
with image size issues with AGG/OpenLayers. 

On your questions, if you think it might be disruptive then perhaps users should opt in (e.g.
 --enable-experimental-png).

I'd go ahead and commit. No sense waiting and that gives more folks a chance to test.

Steve

>>> On 12/12/2007 at 2:46 AM, in message
<d2b988930712120046n1c0dce28ye568b9c693040f0d at mail.gmail.com>, thomas bonfort
<thomas.bonfort at GMAIL.COM> wrote:
> A quick update on this.
> I've now also added quantization for rgba images ( based on the median
> cut implementation of pngquant / ppmquant:
> http://www.libpng.org/pub/png/apps/pngquant.html ).
> 
> examples here (the first two images are actually transparent. you'd
> have to open them in an image editor to see that):
> 
> the full rgba png:
> http://www.terriscope.fr/ms_tmp/rgba.png : 129k
> 
> the quantized rgba png (may look funny under oldish MS IEs)
> http://www.terriscope.fr/ms_tmp/palette.png : 39k
> 
> the output produced with the current gd quantization
> http://www.terriscope.fr/ms_tmp/rgbapalettegd.png 
> 
> I'd personally enable the pngquant quantization for rgb images to , as
> it produces higher quality results, but there's a tradeoff on
> rendering speed (rough times for quantization only: 1.5 sec for
> pngquant vs 0.3 sec for gd, on a 2000x2000 image). Or this could be
> yet another formatoption selectable option.
> 
> Dan: all this will be documented. We've talked with Assefa about
> either writing a complete reference on the different formatoptions,
> and/or a howto on reducing image size with agg (palette, quantization,
> and tradeoffs beween speed/imagesize/flexibility)
> 
> Now for the questions:
> * how should I add this? I'd go for a configure option
> (--disable-experimental-png) with ifdef'd code as I don't know how
> disruptive this would be on all platforms.
> * can I add this soon? It's stable on my setup, but there might be
> issues on other platforms. I'd like to have it tested as much as
> possible before 5.2
> 
> cheers,
> thomas
> 
> On Dec 7, 2007 10:46 PM, Daniel Morissette <dmorissette at mapgears.com> wrote:
>> Sounds like a cool feature. We'd need to make sure it is well documented
>> and not just hidden in the source. A short RFC or ticket for this maybe?
>>
>> Daniel
>>
>>
>>
>> thomas bonfort wrote:
>> > hello list,
>> >
>> > I've added the possiblity to force a color palette for RGBA images. As
>> > gd does not support this kind of images, I had to resort to directly
>> > use libpng functions for the actual saving of the file.
>> >
>> > The steps needed to actually use this would be:
>> > - create a 24 bit rgba image representative of a typical image that
>> > would be produced
>> > - use an external program to create an rgba paletted version of the
>> > image (pngquant, pngnq, photoshop...)
>> > - extract the palette from the created image and save the values in
>> > the form r,g,b,a in a text file (one per line)
>> > - use palette_force and palette formatoptions in the outputformat block.
>> >
>> > This is rather complicated, but usefull on production setups to
>> > minimize image size when using clients that overlay layers (eg
>> > openlayers).
>> >
>> > There are still a few quirks I'd have to work on before the code is
>> > robust enough for inclusion in the trunk, so I'd like to know if this
>> > is a feature we'd definitely like to have before putting too much
>> > effort into that.
>> >
>> > cheers,
>> > thomas
>>
>>
>> --
>> Daniel Morissette
>> http://www.mapgears.com/ 
>>