Material with transparent diffuse color?

[razermail]

Hi everyone. I need your help with making a material with transparent (alfa) diffuse color. I need it for many products that have many color variations, and client wants to set their colors in Photoshop. So I need to make studio/packshot renders (on simple white background), with all reflection and self shadow information, but the diffuse color needs to be transparent (like an alfa). I searched the web but still have no bloody idea how to make such material. Any suggestions?

[maru]

I probably don't fully understand this request, but lowering Opacity will make your diffuse materials transparent (non-white in the alpha channel).

[razermail]

Yes, but this will also affect other properties, like self shadows and reflections becoming less opaque at the same rate. And I need them to stay fully opaque, and only diffuse color to be transparent.

[mferster]

Can you post an example image?

[razermail]

It's something like this - diffuse is transparent, everything else (shadows, reflections, ground etc) are visible, so in Photoshop I can put any color under it to create final, colored render.

[TomG]

There wouldn't be a material to do that, I'd go with a post processing route with render elements (see https://corona-renderer.com/wiki/render_elements and

and the other two videos in that series too maybe), with a mask for the object on the relevant resulting layers in Photoshop (or whatever you are using for post). One thing, while this is fine for a sphere here, for an object with any surface shape, you'll be losing shading on the object that picks out the geometry/shape, so maybe it would be better to have a neutral gray diffuse and use Colorize in post?

[jms.lwly]

As above - a simple way to do this would be to construct the material as it would be with colour/reflection/shadow - and render out a Shadow and Reflect element, as well as some sort of mask/alpha for the object.

Then in Photoshop, mask out the object for filling (or render a matching image without the object at all) - and overlay the Reflect and Shadow elements as Screen (or similar) mode.

There's probably a more technical way to achieve it, but it's a start!