Controlling format of PNG export?

[Ken Ray]

Ben,

All I could find was how to determine the number of colors in an image.
It seems like it's an engine issue, or perhaps creating an external to
do this.

Sorry I couldn't help,

Ken Ray
Sons of Thunder Software
Email: kray at sonsothunder.com
Web Site: http://www.sonsothunder.com/ 

> -----Original Message-----
> From: metacard-admin at lists.runrev.com 
> [mailto:metacard-admin at lists.runrev.com] On Behalf Of Ben Rubinstein
> Sent: Wednesday, April 23, 2003 8:13 AM
> To: metacard at lists.runrev.com
> Subject: Controlling format of PNG export?
> 
> 
> Background: an app which has to integrate with a Director 
> projector; the MC (actually Rev) app generating PNG files 
> with alpha channels, the Director app importing these and 
> doing some further processing and display. (Unfortunately I 
> lost the battle to have the entire solution coded in Rev/MC
> - but at least I am now having daily opportunities to say "I 
> told you so".) An early test image worked fine, we then 
> continued on separate paths.
> 
> Now when we came to put the two together, the mask was no 
> longer being processed correctly by Director.  After some 
> investigation, we found that the Rev/MC app, which had 
> previously been outputting RGB+mask PNG files, was now 
> outputting indexed colour + mask PNG files.  The code that 
> output the PNG files was unchanged; but some additional 
> processing had been done on the images, to turn them into 
> sepia-toned pseudo-ancient images.
> 
> Evidently, the MC engine, asked to export a PNG from a 32-bit 
> + mask image, is cunningly inspecting it and deciding that 
> there are no more than 256 distinct colours, and therefore 
> choosing to optimise the file.  I've no reason to think that 
> these aren't perfectly valid PNG files (PhotoShop at least 
> seems to see the transparency) - it's probably Director's 
> error that it's ignoring the alpha channel if the basic image 
> is not RGB.
> 
> I've frigged it for now by modifying the routine which does 
> the sepia toning, introducing some random variations in the 
> low-order bits of some pixels in the image, so that there are 
> (invisibly to the human eye) more than 256 distinct colours 
> in the image.  But this isn't 100% guaranteed to work for all 
> source images.  Is there any way that I can force Rev/MC to 
> output the PNG as RGB+alpha?
> 
> TIA, 
>  
>   Ben Rubinstein               |  Email: benr_mc at cogapp.com
>   Cognitive Applications Ltd   |  Phone: +44 (0)1273-821600
>   http://www.cogapp.com        |  Fax  : +44 (0)1273-728866
> 
> 
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