Is there a simple way to render an image sequence from an ACES colour space in Houdini directly to an srgb format for posting on Youtube without going through Nuke or another compositor to convert its gamma so it look right?

litote
Is there a simple way to render an image sequence from an ACES colour space in Houdini directly to an srgb format for posting on Youtube without going through Nuke or another compositor to convert its gamma so it look right?

In the AOV tab of karma render settings, there is an "output colorspace" parm. I've never tested that parm. It looks like all the AOVs would be outputted in the set colorspace, but I'd have to test to make sure.
What I've tested is in the filters tab, on the OCIO parm you can set which AOVs to convert from/to colorspace. Works well, but (in H19.5) the viewport render got strange color behavior while it's processing.

I am no so familiar with Karma. Do you know if it can be done with Mantra?

litote
I am no so familiar with Karma. Do you know if it can be done with Mantra?

If you render to mplay, it now has the option to apply a display-view transform when saving to ldr formats or when exporting to video.

litote
I am no so familiar with Karma. Do you know if it can be done with Mantra?

I'm not sure mantra will render in ACEScg space, since it was discontinued in the transition. Probably it's rendering still in linear sRGB, so no conversion needed.

guilhermecasagrandi

litote
I am no so familiar with Karma. Do you know if it can be done with Mantra?

I'm not sure mantra will render in ACEScg space, since it was discontinued in the transition. Probably it's rendering still in linear sRGB, so no conversion needed.

linear srgb and acescg are the same thing as far as the renderer is concerned. The OCIO color config determines the output transform to display from scene linear. If the scene_linear is defined as acescg then your render is in acescg.

Mantra doesn't have the ability to do an ocio display transform as part of the output process, so a post process is required to transform from scene linear to display.

jsmack

guilhermecasagrandi

litote
I am no so familiar with Karma. Do you know if it can be done with Mantra?

I'm not sure mantra will render in ACEScg space, since it was discontinued in the transition. Probably it's rendering still in linear sRGB, so no conversion needed.

linear srgb and acescg are the same thing as far as the renderer is concerned. The OCIO color config determines the output transform to display from scene linear. If the scene_linear is defined as acescg then your render is in acescg.

Mantra doesn't have the ability to do an ocio display transform as part of the output process, so a post process is required to transform from scene linear to display.

for data aov, yes, I think so because they represent raw numbers, but for color AOVs, like beauty, I don't think so, since the primaries are different between sRGB and ACEScg, so I don't think they are the same if the renderer doesn't know about aces.

guilhermecasagrandi
for data aov, yes, I think so because they represent raw numbers, but for color AOVs, like beauty, I don't think so, since the primaries are different between sRGB and ACEScg, so I don't think they are the same if the renderer doesn't know about aces.

The primaries are unknown to the renderer. The RGB values are effectively just data channels. They only become meaningful color values when displayed. Some renderers know the colorspace and primaries for purposes of spectral phenomena, however mantra and karma are not one of them as all spectral conversions are hard coded to use one space.

jsmack

litote
I am no so familiar with Karma. Do you know if it can be done with Mantra?

If you render to mplay, it now has the option to apply a display-view transform when saving to ldr formats or when exporting to video.

Could you give me more detail on how to actually set this up to render? ACES comes with some LUTs, do you apply one of these to convert from ACES to sgrb? How, exactly?

litote
Could you give me more detail on how to actually set this up to render? ACES comes with some LUTs, do you apply one of these to convert from ACES to sgrb? How, exactly?

LUTs are no longer used by ACES OCIO configs as they have been built into OCIO. The conversion is defined by selecting a display-view space which transforms from the scene_linear space also defined in the config. In the Mplay save dialog, for Color Space choose "Bake to OpenColorIO Display/View" and then pick the desired display and view from the other two menus.

Thanks for the screenshot.

I discovered that the option for Color Space: Bake to OpenColorIO Display/View is not available in my version of Houdini (18.5). It only has a LUT option. What version of Houdini are you using for this version of MPlay?

Any idea how I could use the LUT option instead? I don't know what LUT to use orwhere to get it. Some came with my ACE download.

Otherwise, presumably my only option is to try to convert it to .jpg in Nuke from the ACES .exr?

litote
I discovered that the option for Color Space: Bake to OpenColorIO Display/View is not available in my version of Houdini (18.5). It only has a LUT option. What version of Houdini are you using for this version of MPlay?

Any idea how I could use the LUT option instead? I don't know what LUT to use orwhere to get it. Some came with my ACE download.

This was added in Houdini 20.0

litote
Otherwise, presumably my only option is to try to convert it to .jpg in Nuke from the ACES .exr?

With 18.5 the options for export are pretty limited. There is no built in way to apply a display-view transform prior to 20. A config where the view is enumerated as a colorspace could be used with the colorspace transform offered in VEX/VOPs and use a composite network to apply the color transform. 3rd party tools would be the only other way to convert without using legacy methods.

Thanks for your reply jsmack.

I figured out where to dl the LUT I needed and how to apply it in v18.5 in MPlay.

For those interested, these are my steps:
(1) Set a frame range in the Mantra render node if you want to output a sequence.
(2) Either click Mantra node’s Render to MPlay or RMB on film reel icon at bottom left and choose mantra1 (Sequence). An initial MPlay - Render popup will open and then an MPlay popup.
(3) You can show the image correctly in MPlay in usual way by selecting LUT and Gamma in dropdown. To play through the sequence once it is rendered set the frame range in field below.
(4) To save to jpg format with the correct look, with MPLay popup viewer selected, got to File (tab at top of Houdini interface) - Save Sequence As (or Save Frame As if a single image).
(5) In Save As popup, choose a destination folder and jpg extension in Filename field. The Frame Range should show the Mantra setting in first two fields. Check Convert to Image Format’s Colorspace and check LUT and select this LUT found at link below: sRGB for ACEScg Houdini.lut and click Save.
The Rec.709 for ACEScg Houdini.lut may also work. Download from here from an older version of ACES:
https://github.com/imageworks/OpenColorIO-Configs/blob/master/aces_1.0.3/baked/houdini/Rec.709%20for%20ACES2065-1%20Houdini.lu. [github.com]