If it is 24 bits then is RGB(3 bytes) not RGBA(4 bytes=32 bits), so you read 3 bytes put 16rFF (no transparency) in the other byte, as an example see Graphics-Files>>PNGReadWriter>>copyPixelsRGB: 

On 19/09/2010, at 14:17, Schwab,Wilhelm K wrote:

> The library assumes a 24 bit layout; unless I want to edit/recompile it, I have no say in that.  The best I have been able to find is to let it do its thing and then expand the result into what Pharo uses for a 32 bit layout; I take that to be adding an alpha bit to each pixel??
> 
> 
> 
> -------------------------------------------
> 
> Javier Díaz Reinoso javier_diaz_r at mac.com
> Sun Sep 19 18:16:23 UTC 2010
> 
> You need to browse the Graphics-File category, there you can found how the different formats are read/write from files to memory.
> 
> A better name for ColorForm should be IndexedColorForm: 8 bit index into a palette of colors, used also for 8 bit gray images. If you have RBG you need to use 32 (or 16) bit Forms.
> 
> 
> 
> ________________________________________
> From: pharo-project-bounces at lists.gforge.inria.fr [pharo-project-bounces at lists.gforge.inria.fr] On Behalf Of Schwab,Wilhelm K [bschwab at anest.ufl.edu]
> Sent: Sunday, September 19, 2010 1:49 PM
> To: Pharo-project at lists.gforge.inria.fr; squeak-dev at lists.squeakfoundation.org
> Subject: Re: [Pharo-project] RGB (0-255) image format?
> 
> Some searching did not turn up an answer, but I might be able to let the library "think" in 24 bbp, and then use a C function to expand the result into 32 bbp for Pharo.  Would the alpha value be 255??
> 
> Bill
> 
> ________________________________________
> From: pharo-project-bounces at lists.gforge.inria.fr [pharo-project-bounces at lists.gforge.inria.fr] On Behalf Of Schwab,Wilhelm K [bschwab at anest.ufl.edu]
> Sent: Sunday, September 19, 2010 10:55 AM
> To: Pharo-project at lists.gforge.inria.fr; squeak-dev at lists.squeakfoundation.org
> Subject: [Pharo-project] RGB (0-255) image format?
> 
> Is there a clever and fast way to turn an array of RGB triads (each slot taking on uint8 values from 0-255) into a Form, or better yet treat it directly as a Form?  If I understand ColorForm correctly, it uses a map and the image "pixels" are indexes into same.  In this case, I would allocate a block of memory, hand it to a library, and it would blast the RGB values all over it.  Do we have a ready way to use the result w/o having to loop over the individual values?
> 
> I am working on an interface to PLplot (http://plplot.sourceforge.net/).  It is working, but so far only if I save files to disk, which I would like to not *have* to do.  Sometimes (batches in particular), it makes sense to let the code that creates a graph save it, but I also like to do a lot of interactive plotting that should not have to hit the disk.
> 
> Bill
> 
> 
> 
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