Background image too dark vs. png with halo

[rmaytee]

I have a photo I need to use for my background (a common request) and I get an annoying halo around my geometry when I save the image as a png, and add a background in photoshop. I tried just using the image as a viewport background image, and it renders really dark. See images below. Are there any suggestions?

[Alex_M]

In the instance where you've added the image as a background in Max, I assume you've done this via the environment map slot? If that's the case, make sure the "Affect Background" checkbox in "Color Mapping" is disabled. This way color mapping adjustments won't affect your environment maps and they should appear as bright as they are in the material editor. Hope this helps

[super gnu]

render your model against black. add it over the photo after in photoshop. to get complete control over any remaining fringing, i usually make a copy of the cgi on another layer, and use "remove black matte" in ps. then, since that sometimes gives slightly bright edges, i blend it 50% with the un edited version. this generally gives me perfect edges.

[rmaytee]

Thanks you both. I will likely use both methods, depending on the project.

[mattclayton]

I'd definitely recommend rendering out on black. You shouldn't really get any halo-ing with this approach assuming photoshop (or other compositing package) is treating the alpha correctly ie some involve post-multiplying options.

CS6 seems to deal with it correctly these days but in past versions it's been a bit hit and miss. Maybe look at installing ProEXR (http://www.fnordware.com/ProEXR/) Lets you tweak how the alpha is used.

If you do get halo-ing for whatever reason just use the (in PS) Layer>matting>defringe option. Depending on how bad your fringe is increase the pixel range. Photoshop then does some magic to take colours from underneath your render and blend them with the edge of your layer or something...educated guess.

It's worth saying that the first option of keeping the background in render can be done (although i think there may be some exposure issues if you don't do more than turning off affect backgorund) however in the past when i've done this you get some residual image in the refraction on your glass when you really want to get rid of that altogether for comp-ing.

[rmaytee]

Hey guys. Thanks again for all the help with this issue. I have run into an issue working with this method. When rendering a view that doesn't look away from the building, and rendering a more traditional view TOWARDS the building, I would still like the flexibility of rendering a png with black background so I can easily replace the background post. But when I do that, I no longer see the v-ray sky reflected in my glass. How do you get around that?

[super gnu]

you put the vraysky in the "gi" and "reflection" override slots in the render settings. that way the sky will light the scene and show in reflections (and refractions) whilst allowing you to do whatever you want with the max background.

[rmaytee]

Ah, nice! That worked perfectly. I have never used that slot. Thank You!