[MikaelP]

Hi,
Im playing with compositing a chrome object to a image background.
The object is set to reflect a spherical map and the scene has got a plane that catches the shadows.

I have exported all passes, but one, successfully.
Im not able to figure out how to render a black image with only the highlights showing in degrees of white?
The chrome object adds a highlight on the ground plane(sun reflected of the metal) that i want to separate into a pass/channel.

Thanks!

[MikaelP]

So the only way i figured out how to do this is by rendering the ground plane object with the chrome object. I then render only my ground plane.
I then stack these two images in photoshop and blend them with subtract. The result gives me the light reflections on the ground plane.

This seems a bit tedious so i guess there should be a better way?

[seghier]

hello ; you can use 3dsmax or sketchup to project the background on a plane than modify the material of the plane to receive shadow and reflectionan ; and setup the right lights for your scene
render your object and plane with alpha channel and use photoshop for the final step

[MikaelP]

Hi Seghier,
will the alpha channel separate the shadows and highlights from the plane?
Iv got Maya.

Heres a sample render with a sphere. I only need those highlights in the red circle to be rendered on black so that I can make a proper composited image with shadows and highlights on the floor. Seems weird as shadows are so easy to separate to its own channel with two clicks

[seghier]

alpha channel don't separate shadow and reflection from the plane
if maya have camera map you can project the background to a small plane placed under the sphere the plane receive shadow and other effect
if you see that the small plane more bright or dark than the background ; you need render your scene with alpha channel than open the background in photoshop
; import the render and correct the brightness

[polynurb]

hide object from cam?!
if you render a shadow channel at the same time, you can knock the shadow from the beauty pass.
but don't ask me about the industry standard to do this.. here it is an inverse linear dodge with 36%

*divide could be the way to go

[MikaelP]

Thanks Polynurb,

Knocking out the shadows works quite well with divide.
Then i only use difference with the knocked layer and a layer thats a render of only the same surface, without any shadows or highlights, and i actually get quite close what I'm looking for.

Would still hope to find a easier way as the resulting layer has some manual cleanup to be done with a black brush.

[eric nixon]

I would render that caustic highlight as a seperate pass, using a black ground (with some spec) hiding the ball to cam, etc.

[MikaelP]

Hi Eric,
thats my next plan. I guess you just have to balance the amount of spec so it still looks like the material where the caustcs are cast on(on the image you use for the composite). And maby bump the exposure to get are more prominent effect for more playroom in photoshop.