Question: Rendering one object and hiding others??

Eyos

I need to render an object without showing the rest of the scene, but keeping the lighting that is reflected on the object from other items in the scene. Something like Multi-pass, but for a selected object. Is this possible? :roll:

stu sutcliffe

I would like to do this also.But I dont think it is possible. For bounced light from something that is hidden ,what I have done is put a coloured plane just out of shot and bounced of that ...a bit harder to do for shadows though.

evilproducer

So, do you mean the object is reflective and you need to see the reflections of the other elements of the scene? Or do you mean you have a scene that uses GI (Indirect Lighting) and you need the light that is reflected off the the other objects in the scene?

A possibility with both scenarios could be to render the scene with a spherical camera with the object that is supposed to be by itself hidden, and then place the spherical render in the Scene's background slot and hide or delete the other scene elements that you don't want to see. If you enable Skylight in the render room, you'll get an approximation of the light in your scene as Carrara will treat the spherical render as an IBL- similar to an HDRI, but not as accurate. Then render with the alpha channel enabled in the render room.

If it's just reflections you want, the spherical render will reflect in the surface of the object you're rendering.

It's kind of hard without having a better idea of what it is that you want to do, what your lighting is, what your surfaces are, etc.

Eyos

evilproducer said:

So, do you mean the object is reflective and you need to see the reflections of the other elements of the scene? Or do you mean you have a scene that uses GI (Indirect Lighting) and you need the light that is reflected off the the other objects in the scene?

A possibility with both scenarios could be to render the scene with a spherical camera with the object that is supposed to be by itself hidden, and then place the spherical render in the Scene's background slot and hide or delete the other scene elements that you don't want to see. If you enable Skylight in the render room, you'll get an approximation of the light in your scene as Carrara will treat the spherical render as an IBL- similar to an HDRI, but not as accurate. Then render with the alpha channel enabled in the render room.

If it's just reflections you want, the spherical render will reflect in the surface of the object you're rendering.

It's kind of hard without having a better idea of what it is that you want to do, what your lighting is, what your surfaces are, etc.

I only need to have the light that is reflected from other objects in the scene, the object itself is not reflective.
I will try the spherical camera and see how that works.

In the mean time, I managed to bypass the issue with a bit of manual work: I rendered the object while hiding all the rest of the scene (I kept the lights as they are, without changes, but the object as expected was darker). This way I got the object with Alfa at its edges. I then rendered the full scene and copied in post the inside the object from the full scene onto the first stand alone render, being careful not to override the semi-transparent edges of the object. It's a bit of work but the result seems OK so far (I have other object and see how that goes).

Eyos

Thanks Evilproducer for the technique you suggested above, it gave me a clue how to go about it.
I found a way which does not take too much time to set, and is based on planes which are set to shadow catchers.
I describe it below if others will have the same need:

1) Set a plane below the object and one behind the object.
2) Make them small as possible but keep a narrow gap between the edge of the object and the planes.
3) Plane below: Set the shader of the shadow catcher below the object to 'Catch shadow' and 'Show in alfa channel'.
4) Plane behind: Set the shader of the shadow catcher behind the object to 'Show in alfa channel', and UN-Check 'Catch shadow'.
5) Plane behind: In properties\general tab, UN-Check 'cast shadows' and UN-Check 'receive shadows'.

tbwoq

Hi Eyos.

The render room Irradiance Map feature will save bounced diffuse lighting(Sky Light/Indirect Light) as a map. You can exclude/include new objects and textures when you render again with a saved IR map. For instance. You can render a sphere on a plane with indirect light and save the IR map. Then in the plane objects general tab properties, uncheck Visible and render the scene again with the saved map option. The sphere will still have the bounced(irradiance map) lighting.

Eyos

tbwoq said:

Hi Eyos.

The render room Irradiance Map feature will save bounced diffuse lighting(Sky Light/Indirect Light) as a map. You can exclude/include new objects and textures when you render again with a saved IR map. For instance. You can render a sphere on a plane with indirect light and save the IR map. Then in the plane objects general tab properties, uncheck Visible and render the scene again with the saved map option. The sphere will still have the bounced(irradiance map) lighting.

Hi tbwoq, thanks for the tip, this can be very helpful, also in upcoming animation - saving a lot of rendering time.
I learn something new here every day - keeps my decaying gray matter in shape...

evilproducer

Eyos said:

tbwoq said:

Hi Eyos.

The render room Irradiance Map feature will save bounced diffuse lighting(Sky Light/Indirect Light) as a map. You can exclude/include new objects and textures when you render again with a saved IR map. For instance. You can render a sphere on a plane with indirect light and save the IR map. Then in the plane objects general tab properties, uncheck Visible and render the scene again with the saved map option. The sphere will still have the bounced(irradiance map) lighting.

Hi tbwoq, thanks for the tip, this can be very helpful, also in upcoming animation - saving a lot of rendering time.
I learn something new here every day - keeps my decaying gray matter in shape...

I learned something as well! Thanks tbwoq!

tbwoq

Glad the info helped.

The irradiance map feature is also nice if you wanted to adjust or change some textures after saving a map for a different look or effect.

sirgatsbymail

I have read everywhere about irradiance map, but how i do it ? can somebody make step by step how to save an ir map from an scene and after use it to render only 1 object from that scene but keep lights and reflection of others objects ?