How to use rgb grid volume

[cnexah]

In the tutorial for volumetric inverse rendering, the setting for the grid volume is:

scene_dict['object'] = {
    'type': 'cube',
    'interior': {
        'type': 'heterogeneous',
        'sigma_t': {
            'type': 'gridvolume',
            'grid': mi.VolumeGrid(dr.full(mi.TensorXf, 0.002, (v_res, v_res, v_res, 1))),
            'to_world': T.translate(-1).scale(2.0)
        },
        'scale': 40.0,
    },
    'bsdf': {'type': 'null'}
}

I was wondering if I can add rgb color to the grid volume? Each voxel has a different color?

[cnexah]

I tried the following code, is it possible to have rgb abledo instead of gray?

scene_dict = {
    'type': 'scene',

    'integrator': {'type': 'prbvolpath'},

    'object': {
        'type': 'cube',
        'bsdf': {'type': 'null'},
        'interior': {
            'type': 'heterogeneous',
            'sigma_t': {
                'type': 'gridvolume',
                'grid': mi.VolumeGrid(dr.full(mi.TensorXf, 0.002, (v_res, v_res, v_res, 1))),
                'to_world': T.rotate([1, 0, 0], -90).scale(3).translate(-0.5)
            },
            'albedo': {
                'type': 'gridvolume',
                'grid': mi.VolumeGrid(dr.full(mi.TensorXf, 0.002, (v_res, v_res, v_res, 3))),
                'to_world': T.rotate([1, 0, 0], -90).scale(3).translate(-0.5)
            },
            'scale': 40
        }
    },
    'emitter': {'type': 'constant'}
}

[njroussel]

Hi @cnexah

This is indeed supported by the albedo parameter in a heterogeneous media: https://mitsuba.readthedocs.io/en/latest/src/generated/plugins_media.html#heterogeneous-medium-heterogeneous

In your snippet you're using the same value in all three channels, hence the gray color.

P.S: Please format your messages properly 😄