In article <3bebd8a8@news.povray.org> , Warp <war### [at] tagpovrayorg>  wrote:

> : and doing so causes lots of problems
> : as no other program (that I have) expects it that way.
>
>   What problems?
>
> :  In particular is
> : makes the images unusable without alpha channel display always on...
>
>   But that's absolutely normal!
>   The alpha channel contains essential information about the image. It tells
> how the pixels should be blended against the background in order to get the
> correct result. If an image viewing program does not take into account the
> alpha channel then it's dropping out this essential information, thus
> destroying the original image.
>   The image is unusable without alpha channel because it isn't even supposed
> to be usable. There isn't anything wrong here.

Ok, take Photoshop for example (version 3.0, I am not a millionaire!).  If
one draws with a brush using i.e. blue color on a transparent layer and then
gets a historgram, it will show you only perfect blue.  So what it at least
seems to do, is to set all anti-aliased pixel color component values to pure
blue.  POV-ray on the other hand (for obvious reasons) will determine a
middle value for both the color and the alpha-channel, which in turn is
fixed by saying the background is always black.  Of course this does fix the
problems without this assumption, but it isn't perfect.

For now (as discussed outside this group) the best solution for POV-Ray is
be to use antialiasing bailout based on the alpha-channel rather than the
color value.  Of course there are still a few minor implementation details
to be worked out (so this may not be in beta 8) first...

    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

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

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