In article <371### [at] aolcom> , Bob Hughes <inv### [at] aolcom>  
wrote:

> I only just recently tried alpha channel output +UA as a png file and
> then used that as an image file and saw nothing different.

Did you use a sky_sphere? The alpha-channel will only work with background.

> Yes, transmit and filter were applied to 'all'. Maybe it did, maybe it
> didn't change it, I was looking for the obvious.
> Opening the file with PSP showed the image to definately have Alpha as
> compared to a non-Alpha png. Thing is PSP couldn't show anything there,
> just black or blank, even if I added a second channel in with PSP
> itself.
> I also used Bits_per_Color to increase the "bandwith" so to speak to
> make room for 8 bits of transparency info in that Alpha Channel.
> I never understood it to begin with, and now I know why. I agree, the
> only way to learn is if others have used it and can manage a
> tutorial-like explanation or a word of sense about it at least.

Well, actually it is easy:

An alpha-channel is a fourth component saved with each pixel. It determines
how much of the background behind an image comes through. This is usually
useful for editing the image later in Paint Shop Pro, Photoshop or Gimp(?)
and combine it with other images.
In POV-Ray you need to do some setup to get an alpha-channel output:
- Set the alpha-channel option +UA or Output_Alpha=true.
- To get a full alpha-channel, make sure Bits_per_Color is set to 8.
- Make sure you don't use sky_shpere {}. The alpha-channel will only be
visible when using background {}. During rendering you will still see the
background, no alpha-channel (except on POV-Ray Mac which can preview the
alpha-channel).
- To make objects (half) transparent in the alpha-channel use the transmit
color component - filter won't work. A value 1.0 is full transparency.

I hope this explains how to use it. :-)


    Thorsten


____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: Tho### [at] csicom

Visit POV-Ray on the web: http://mac.povray.org

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