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Author Topic: Alpha Problem with Forest Objects  (Read 2094 times)


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Alpha Problem with Forest Objects
« on: October 28, 2015, 08:50:29 PM »

I have a little question about Transparency against the background with Forest Objects ( here: HQ Plants 1 - Birch 10 + Common Tree 1 and they don't use cutout or opacity maps ).

I'm using 3ds Max 2015 and mental ray + FG with a mr daylight system, mr Physical Sky as a environment map, mr photographic exposure control with checked process background / environment maps. Unified Sampling qualitiy 1,5 - 1/128 with mitchell 4/4

You can see in the attached screenshot white edges around the Forest Objects - 3ds Max Objects ( the roof ) has not such edges. This edges are still visible against a background image when doing post-pro. I know there are a few workarounds in photoshop to make this effect disappear BUT even a workaround is still additional extrawork.

Does anyone know what to do to ged rid off this edges ? What settings are responsible for this problem?

« Last Edit: October 29, 2015, 08:36:20 AM by suppenhuhn »
iToo has probably the best support & community i know !!

I'm using it with Max 2019 & Vray 6

Michal Karmazín

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Re: Alpha Problem with Forest Objects
« Reply #1 on: October 29, 2015, 04:11:16 PM »

Thought it might seem so, it's not a Forest related issue. As you can see on the first attached image where on the left side are Forest objects and on the right side mesh objects, the result is exactly the same. This halo artefact comes from anti-aliased alpha channel.

The issue is tight to premultiplied alpha channel rendered against non-black background. For post-production purposes in Photoshop would be easier to not use the Environment Map for Background (and render the image just with black background).

This tip is mentioned also on the Autodesk's site regarding this topic:

"If you plan to composite objects in another program such as Combustion or Photoshop, render the objects against a black background. Otherwise, a fringe of environment or background color can appear around the objects. "

Let me mention, that for these purposes, there is a handy tool in Photoshop: Layer > Matting > Remove Black Matte or Layer > Matting > Remove White Matte.

Hope that helps.

Best regards,
« Last Edit: October 29, 2015, 04:34:35 PM by Michal Karmazín »