Render a Digital Projection Screen or Flatscreen TV

[STECJASON]

I install artist's video shows, and I'm looking for a work flow that will allow me to import a still image from a video into Sketchup and render it as if it were a projection in a movie theater. I've gotten close by using emissive materials. The reflection colors the theater in light the same color as the still image. But, I'm having a hard time isolating the exposure of the theater. When I get the emissive material (the projection screen) right the theater is too dark and vice versa. There is a check box that is supposed to isolate the emissive material, which is how I read it's function. "Compensate EV ? Used when rendering with the V-Ray Physical Camera. When enabled, the intensity of the material will be adjusted to compensate for the camera exposure." But, I when I change the camera's exposure it adjusts both the emissive material (the projection screen) and the theater.

I suppose I could mask out the screen and then render the gallery separately, but I hope to avoid that step.

Any tips would be greatly appreciated.

Thanks,

Jason.

[Peter.Chaushev]

Hello, Jason,
Having the Emissive material's "Compoensate EV" checkbox enabled while adjusting the Exposure value ensures the emissive color/texture is rendered the same at all times.
Could you please state the version of V-Ray for SketchUp you are using and also share a couple of screenshots of your scene setup to better illustrate your issue?

Kind regards,
Peter

[STECJASON]

Hi Peter,

I am using Sketchup 18.0.16976 and just downloading V-Ray for the fist time a month ago.

I do see the Compensate EV check box working now. Not sure what the stumbling block was. My emissive material in this case is a relatively dark projection, so I'm dealing with the fact that it does not illuminate the gallery with quite the right intensity, despite some extreme camera adjustments. I've made the material's intensity as high as I can without 'blowing it out'.

I've attached a render I did using an invisible rectangular light colored like the lime green of the material. Then the screen shots of just theemissive material render set-up.

Best,
Jason.

[Peter.Chaushev]

Apologies for the late reply!
There is no straightforward way to preserve the same intensity of the screen while increasing its emissive light (not physically correct). Furthermore, using extreme exposure values pretty much guarantees bad sampling and may impedes the Denoiser functionality.

The Emissive material's Compensate EV checkbox should be enabled.
You can then either slot it into a Wrapper material and bump the Generate GI value or slot into an Override material and use for GI a copy of the Emissive material with bumped intensity.

However, the recommended way to do this would be to simply leave the screen material as it is and instead place an invisible Rectangle Light in front. V-Ray works faster with direct light sources instead of those which rely on GI, so this solution will be cleaner, faster, and allow better intensity control without having to change the EV.
You can either adjust the light color to approximate the emissive material's overall texture or just use the same texture on the light.

Kind regards,
Peter