Hi guys,

I want the background image be visible in the object's refraction, so I add my desired image to a "Background Plate" LOP, and to my camera background Image file tab too, but it doesn't work!

How can I fix it?

Thanks for helping.

You can try the old trick of parenting a grid with the image to your camera. Then the background plate will be a "real" object in the scene which can reflect rays.

Masoud
Hi guys,

I want the background image be visible in the object's refraction, so I add my desired image to a "Background Plate" LOP, and to my camera background Image file tab too, but it doesn't work!

How can I fix it?

Thanks for helping.

Is this karma xpu or karma cpu? the background plate lop doesn't work with karma xpu. It was supposed to work in houdini 20 but it does not. The background plate lop has a vex based material and vex based materials only work with karma CPU. There is supposed to be a materialX material in the background plate lop for xpu, but it isn't there. Sidefx logged this as a bug when I reported it a few months ago.

@Enivob
Hi Enivob, I know that trick but I want to find the right way to use Karma features.

@evanrudefx
Hi there, I tried both XPU and CPU, but the same results.

Masoud
@evanrudefx
Hi there, I tried both XPU and CPU, but the same results.

I see the reason it isnt working from your photo. You have to plug in the second wire and turn on import render vars from second input on the karma render settings.

Hi @evanrudefx, no it doesn't fix the problem.

Masoud
Hi @evanrudefx, no it doesn't fix the problem.

You should post the hip file so I can see what you are doing wrong. Even if that didn't fix it those changes needed to be made.

edit: I see the other issue. In your photo you dont have a primitive to use as a holdout. You need to place a grid or some type of geometry behind the sphere and assign it as the primitive to use in the background plate lop.