View Full Version : Alpha Channel Bug

01-20-2005, 10:03 AM
Hi there,

I can't work with v8.2 because the alpha channel results are wrong. I need to compose things together in Photoshop but this seems to be impossible.

If you turn on 'Ray Trace Reflections' the alpha channel shows the reflected area. I think that's simply wrong and I would like to have it that way it worked with the previous versions.

I really appreciate updates but at this time I am wondering if anyone of the programmers rendered an image and took a quick look at the result of the alpha channel.

I hope this will be fixed soon as it makes compositing impossible!

Thanks in advance and have a great day.

01-20-2005, 12:42 PM
That's rather disturbing, to say the least.

I've tried to test a similar setup here, but the alphas come out just fine.

Can you provide more details of your scene, or perhaps post an example scene?

Also, it looks like somthing odd is going on with your "table top". In the lower right image, with reflections turned off, wouldn't the alpha normally show the table poly? Instead it's kinda faded out under the monitor like it has a transparency map...


01-20-2005, 05:48 PM
Thanks for your reply. :)

For the shadow I have applied 'Shadow Density' under Surface Editor - Advanced Tab, so I should only get the shadow from that plane in the alpha channel.

I have attached a simple scene so you can see what the Alpha Channel shows.

Cheers ;)

01-20-2005, 07:04 PM
Yikes! That's a right nasty bug there! Worked fine in 8.0.1.

When a surface has any Reflection, and the surface's Alpha Channel is set to Shadow Density, the relfections are being added to the alpha along with the shadows.

This is definitely wrong.

If you haven't sent in a bug report yet ([email protected]), please do. I will also.


01-21-2005, 01:26 AM
I haven't tried it yet with 8.2, but our free AlphaRalpha plugin may be able to fix that alpha channel http://www.tufflittleunit.com/alpharalpha.htm


01-21-2005, 01:59 AM
You can also solve this problem by having clones of your geometry with white Colour and 100% Lum, render the exact motion is a different scene.


01-22-2005, 04:48 AM
HI !

I tested Lw 8.2 on P4 2.8GHz , WinXP pro SP1, 2GB Ram, 3DLabs GFx and YES this is a BIG BUG :(. Makes composting with alpha channels pretty problematic. And i also confirm that LW 8.0.1 works fine so it must be something in new raytracing code or like that :(.

Lucky i saved 8.0.1 on my HDD so i can use them both :).