Diffuse render element - Change colour in post

[DanSHP]

https://docs.chaosgroup.com/display/...yDiffuseFilter

See link.

"The Diffuse Filter Render Element is useful for changing the appearance of many passes when it is combined with Raw render passes (like VRayRawGlobalIllumination, VRayRawLighting, etc.). In the example below, the Diffuse Filter is multiplied by the Raw Global Illumination Render Element to provide the Global Illumination element. In this way, color correction can be performed upon the raw pass without the actual diffuse colors being changed, making it possible to tint a pass in a realistic way without re-rendering.

The Diffuse Filter is a very useful render element due to the number of raw passes with which it can be combined, giving the ability to manipulate many areas of the render at the composite level. The Diffuse Filter pass can also be color-corrected on its own, as shown in the example below. In this case, a Multimatte Render Element was used in conjunction with the Diffuse Filter render element to isolate the dangling light and change its color from white to blue without also tinting its lighting or shadowing in any way"

I'm a little confused here. Using the white to blue lamp example shown in the link, I don't really feel it is explained very well.

I have my multimatte ready to alter the colour of an object in my scene without altering the shadows and lighting. I've masked the diffuse element with the multimatte and changed the colour of the diffuse element within the masked area, what next?

[joconnell]

Right!

So if you're doing a simple breakapart and recombine of a vray render, it's pretty much get all of the various different passes containing light (lighting, global illumination, reflection, specular, refraction and sss) and you plus / add all of those on top of each other or linear doge in photoshop.

The simple lighting passes listed above are made up of two components, the colour of the object in your scene and the amount of light that falls on it. If you want to be able to treat these two parts separately, you can either do some simple compositing operations or you can try the raw passes from vray. The colour of an object in your scene gets put into the diffuse filter pass as you've found and to get the light on it's own, you can either use the "raw" version of the lighting and global illumination passes from the render elements, or if you want to go the recommended route use the regular lighting and gi passes, then in your compositing software, divide them by the diffuse filter pass. Since a light pass in vray = diffuse colour x amount of light then you can just use divide to separate them out.

Once you've got your lighting on it's own, you can use your multimatte setup to tweak the colour of your object in it's flat, unlit stage, then multiply your raw lighting back on to restore things to a regular lighting pass.

[DanSHP]

So in order to accomplish this, I would need to go full on render element (GI, Reflect, refract etc etc) composition to RBG beauty pass?

[joconnell]

If you only have one set of pixels then you can't separate out what's in the specular, what colour and brightness the light was and so on. As you say to do this type of adjustment properly then you'll need at minimum lighting, GI, diffuse filter, specular and reflection. Optionally refraction if you've any glassy objects in the scene and SSS if you've anything using translucency.