Image brightness mystery

[zchen]

Hey guys,
I'm setting up a studio scene in which I will build and tweak all my shaders.

However, before need to make sure the colorspace is right and there seems to have quite some paradoxical issues:

- the grey ball is 100% matte with a 128-128-128 as diffuse (to get 50% grey); but it is coming out definitely too bright
- the macbeth chart on the other hand, is coming out too dark (see comparison with the actual bitmap file used); is there a way to make the material show the bitmap, WITHOUT being affected in any way by the scene's light and exposure, as if I'd paste over the image onto the rendered image.

*both are not receiving/casting shadow/reflection.

The setup is lit with one single studio hdr file at 1.0 multiplier.
All bitmap files are loaded with 'Automatic' gamma. The 3ds max gamma is correctly set up.

What do you think could be the issue there?

Thanks!

[FrostKiwi]

Just because the HDR is used with a 1.0 multiplier, does not make it light the scene up with a 1:1 albedo ratio.
It only means that the HDR brightness is not being changed, so naturally it acts as a big light with many brightness values.

- the grey ball is 100% matte with a 128-128-128 as diffuse (to get 50% grey); but it is coming out definitely too bright

Just because the ball is 128 bright doesn't mean it will be 128 bright after being lit by a light, it will naturally be brighter if the light adds energy, or the 158 in your case.

the macbeth chart on the other hand, is coming out too dark

The chart is darker, because it either faces a dark hdri side or is lit at an angle, so naturally it loses light energy.
Nothing wrong here - just physical correctness. Everything works just as it should.

is there a way to make the material show the bitmap, WITHOUT being affected in any way by the scene's light and exposure

Yes, you can use the Corona ray switcher mtl to do that, there is a tutorial for this exact issue. At some point, floating just an image without affecting anything is mentioned at one point.

[romullus]

*both are not receiving/casting shadow/reflection.

If you're doing this with object properties, then please don't. This isn't correct way, use rayswitch material instead.

is there a way to make the material show the bitmap, WITHOUT being affected in any way by the scene's light and exposure, as if I'd paste over the image onto the rendered image.

Yes, there is, it's called CoronaOutputMap. Plug your textures through it and make sure affect by tonemapping is unchecked.

[maru]

Material unaffected by color mapping - as already mentioned, use CoronaOutput map.

Some fun facts:

How to read "real world" light intensity from rendered image:
1) set up scene in correct units and scale
2) set up light sources with correct size, units, and intesity
3) optionally, for best fidelity, use PT+PT and set MSI to really high value (more than 100, higher = closer to reality)
4) disable any tone mapping, (even set gamma to 1.0!)
5) render
6) read data from VFB (right click on pixels). Interpret the numbers as "Watts per meter squared per steradian reflected into camera" - "original RGB" 1,1,1 should mean 1 W/(sr.m^2)

[zchen]

Thanks a lot guys, I will try all those corrections.
I thought initially that the RaySwitchMaterial is used so that the object doesn't affect the surrounding, instead of not being affected BY its surrounding.