composite slightly brighter than RGB pass

[Guest]

Is there any reason as to why a composite in Photoshop would end up being slightly brighter (not quite double gamma) than the RGB pass? It is for a specific scene only as all other scenes I have rendered this way in the past composite exactly as they should and match exactly. My typical workflow is do not affect colours on, linear multiply, gamma 1.0 for output in 3ds max gamma prefs. Save out as 32bit EXR. Saving all the correct render elements such as diffuse, raw GI, raw lighting, reflection and refraction.

If I reduce the opacity of the reflection pass in Photoshop to around 50% I get almost the exact result as the RGB, but I don't think this is the issue. I wondered if the reason was down to using HDRI IBL or materials that have blends in them? I also tried compositing without raw and just included the diffuse in the GI and lighting passes but still the same result. I am going to composite it again today on another computer which has adobe CS5 and see if it works then, as the other has Adobe CS6. I wondered if it could be a colour space issue?

Maybe I am missing something obvious or I ticked a box I shouldn't have but I am stumped where this error might be?

[Guest]

Ok, its not Photoshop as the same thing happened in CS5 as well. I also figured out it only does it for one material this is highly reflective. Everything else in the scene composites correctly. This material is a blend material I wonder if this is the cause?

[Guest]

Ok, tried various things such as turn off glossy highlights, change reflection to affect all channels but nothing works. I have attached a link to the PSD of the comp and the RGB pass, as well as the Max file. The teapot on the right that's green composites fine but the brushed black one doesn't and is much brighter than the RGB pass.

Any ideas what I have done to get this error?

https://www.dropbox.com/sh/9w2uvwr6nyc616q/uKa4ln2vbh

[stef.thomas]

I had the same problem recently with a grass material that was also a blend being brighter when comped. Interested to see if you figure out the cause!

[Guest]

I am glad someone else has had the same issue with a blend material. here's hoping for a fix

[Guest]

Used V-Ray blend material and it works perfect so it doesn't work with 3ds Max standard blend material.

[joconnell]

3dsmax materials don't output the correct shader info needed for vray render layers, best avoid them entirely.

[svetlozar.draganov]

VrayBlend Material and VrayCarPaint material cannot be composed - the result will be always different > darker or brighter.
The only way to compose it is to subtract your final composition from Beauty pass - and then add this result to your composition - this operation will usually fix the difference in unsupported materials and will give you some control over this part of your rendering.