Clamping applied to Viewport Renders

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Tim Crowson
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Does Houdini clamp the max pixel brightness for viewport renders? We're seeing clamped highlights in the viewer, but disk renders seem correct, with the full range.
Edited by Tim Crowson - Aug. 16, 2022 19:19:33
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By viewport do you mean opengl? I wasn't aware of any clamping difference between interactive and non-interactive renders for karma.
Karma clamps camera rays by default at 10. I usually unclamp primary rays, or at least raise it to 100, since 10 is well under the value mapped to the whitepoint under ACES RRT.
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Using the viewport pixel inspector it does seem like values are clamped to 1, regardless of what Color Limit is set to for the Viewport Settings, or which rendersettings prim is being used in the Display Options. Maybe that's to aid the interactive denoiser? When viewport renders are saved to exr they appear to have the full range.
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Siavash Tehrani
Using the viewport pixel inspector it does seem like values are clamped to 1, regardless of what Color Limit is set to for the Viewport Settings, or which rendersettings prim is being used in the Display Options. Maybe that's to aid the interactive denoiser? When viewport renders are saved to exr they appear to have the full range.

Oh, I think the pixel inspector is clamped.
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jsmack
Oh, I think the pixel inspector is clamped.
You had one job pixel inspector!
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Siavash Tehrani
jsmack
Oh, I think the pixel inspector is clamped.
You had one job pixel inspector!

it's more likely the framebuffer the inspector is sampling from is clamped, but if you send it over to mplay with the sidebar button it should work fine.
Tim Crowson
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Well something is definitely clamped somewhere. The pixel inspector doesn't seem to be able to show me values above 209 (or 0.8196). But is that because of a limitation with the pixel inspector, or because the viewer is clamping the output?

Attaching screenshots from a quick test. Rendering this to MPlay shows more range.

(Obviously since we have to do our lighting in the viewport, we need to be able to control clamping in the render settings and see that expected result in the viewport render... i.e. not have additional clamping applied)
Edited by Tim Crowson - Aug. 17, 2022 12:44:39

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mplay.PNG (166.2 KB)
clamped.PNG (111.7 KB)

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Tim Crowson
Well something is definitely clamped somewhere. The pixel inspector doesn't seem to be able to show me values above 209 (or 0.8196). But is that because of a limitation with the pixel inspector, or because the viewer is clamping the output?

Attaching screenshots from a quick test. Rendering this to MPlay shows more range.

(Obviously since we have to do our lighting in the viewport, we need to be able to control clamping in the render settings and see that expected result in the viewport render... i.e. not have additional clamping applied)

The pixel inspector is useless, it's giving the pixel value on screen (post lut), not in the render.

Why is your image rendered clamped though? Are you using a renderer other than karma?
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It's not clamped before viewing lut is applied for me (inspector still samples post lut, so can't sample above 1):

Attachments:
pig_un-tone-mapped.png (727.5 KB)
pig_shotlook.png (727.2 KB)
pig_shotlook2.png (725.6 KB)

Tim Crowson
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This was with Karma (although I see the issue with other delegates too). We have a LUT in place here (although it's neutral in this case). That same LUT doesn't clamp anywhere apart from this viewer though. Even that MPLay render had that LUT in play.
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Tim Crowson
This was with Karma (although I see the issue with other delegates too). We have a LUT in place here (although it's neutral in this case). That same LUT doesn't clamp anywhere apart from this viewer though. Even that MPLay render had that LUT in play.

By lut, do you mean a look defined in an OCIO config, or an actual old school lut? I haven't tried using luts directly in a viewer in years, so it could be that luts are applied post clamp.
Edited by jsmack - Aug. 17, 2022 14:37:40
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