ACES and background images

[piotrus3333]

I'm afraid I seem to be quite lost with the texture conversion I mapped my image to a dome and I rendered it (means no more Background layer anymore). However, no matter how I set the VRayOCIO node, I can't get the render to look the same as the JPG image I mapped. Help, pls.

https://forums.chaos.com/forum/v-ray...47#post1221547

edit: dome light expects a texture in the rendering space. linear sRGB or ACEScg.

[hermit.crab]

piotrus3333 gave a more elegant solution. I tested the OCIO config in the Background layer and on a texture (8-bit), and it works very well. However, as he mentioned in the linked thread: " Aces display transform, when inverted, creates float values of a bit over 16. This might not always be enough for sky, etc. Be aware of this and correct when needed."

[seandunderdale]

This was a life saver! Ive been having to avoid using ACES 1.0 SDR-video in my shots that use a backplate since I could never get it to look correct. Totally agree that these OCIO supplied by Marcin in the other thread should be shipped with Vray (Or Maya) I had no idea they existed. Id been using ACES1.0 SDR for full CGI projects only as I love how it looks, but could never get it to work with backplates. Christmas comes early!!

It also lets me load in pure white background from file and not have clamped to 0.812! which you cant do with ACES 1.0 SDR and the swatch colour value. If you use the swatch, max brightness you can get is 0.812

[david_slachta]

https://forums.chaos.com/forum/v-ray...47#post1221547

edit: dome light expects a texture in the rendering space. linear sRGB or ACEScg.

Thank you, Marcin! This is incredible. With your guide in the other thread I was able to get the dome matching the 8bit JPG and also a regular texture on an object is looking just like the original sRGB image. It's awesome!

I still have an issue with the 32bit EXR plugged into the dome, though. It doesn't look the same as in Gamma 2.2 workflow and the light that comes out of the dome is super freaked out. I guess the setting for the VRayBitmap and VRayOCIO should be different for 32bit than 8bit? I tried to use "scene-linear Rec.709-sRGB" as the input ColorSpace in the VRayOCIO node, but that made the dome look like the regular ACES workflow.

By the way, thank you so much again for providing us with the OCIOs and the guides. I can't believe how many useful topics in regard to ACES there are already. I think all these should be pinned or compiled somewhere for everyone who wants to start with ACES can see and read...

piotrus3333 gave a more elegant solution. I tested the OCIO config in the Background layer and on a texture (8-bit), and it works very well. However, as he mentioned in the linked thread: " Aces display transform, when inverted, creates float values of a bit over 16. This might not always be enough for sky, etc. Be aware of this and correct when needed."

Oh, hmm, for the 32bit EXR I use currently, I measured the float value at the center of the sun to be slightly over 100,000. Would that get clamped down to 16?

Edit: By the way, there's one thing that bothers me on the ACES tone mapping. The shadows and darker tones look very crushed and super dark. Is there a way to get them back?

[piotrus3333]

david_slachta
I guess you are talking about matching exr environment map to its jpeg preview. exr is most likely linear rec709: linear transfer function and srgb primaries in VRayBitmap. it will look different through aces view transform as the preview was created with some other view transform.

aces view transform is known for being quite heavy handed - you can correct shadows with curves layer or simply pick rec1886 display - it’s gamma 2.4.

[david_slachta]

I'd like the EXR rendered in ACES to match rendering the same EXR in Gamma 2.2 workflow. Below is a comparison. On the top left is a rendering of the EXR in the Gamma 2.2 workflow, then on the bottom left is the same EXR opened in Photoshop (the two are matching). The image on the right is the render in ACEScg. You can notice it is higher contrast, and the sky is tone mapped and the highlights are rolled off. This render was done by plugging the VRayBitmap directly into the dome, without the VRayOCIO map. Is there any way to set the VRayOCIO to make the render matching the Photoshop preview or the Gamma 2.2 render?

Aside from looking different, I wonder if the light emitted by the dome is different as well?

[piotrus3333]

I'd like the EXR rendered in ACES to match rendering the same EXR in Gamma 2.2 workflow. Below is a comparison. On the top left is a rendering of the EXR in the Gamma 2.2 workflow, then on the bottom left is the same EXR opened in Photoshop (the two are matching). The image on the right is the render in ACEScg. You can notice it is higher contrast, and the sky is tone mapped and the highlights are rolled off. This render was done by plugging the VRayBitmap directly into the dome, without the VRayOCIO map. Is there any way to set the VRayOCIO to make the render matching the Photoshop preview or the Gamma 2.2 render?

Aside from looking different, I wonder if the light emitted by the dome is different as well?

yes, light would be different. just use jpeg for background and exr for lighting.

what you see in PS is just srgb curve on the exr.