rendering in 32bit linear colorspace?

[JasonA]

HI All,

Im getting unexpected results when rendering to EXR from Terragen in that when i bring my footage into Nuke, it doesnt seem to be in the correct colorspace.  It is a 32bit file which I did expect, but the footage looked quite a ways off from the render view in terragen.

I noticed that there is a Gamme Adjust value which is by default set to 2.2.  I expected that this would put my render in the renderview window in sRGB space, and that by setting this value to 1, i would get a linear render.  However when I re-rendered the scene, nothing in the renderview changed which also was unexoected.  It would seem that the gamma adjust doesnt work in a way i thought.

I'm pretty new to terragen, but I use a linear workflow in maya and nuke and would like to be able to do that in terragen as well.  But judging by whats happening with my footage, im clearly not doing something right.   Can someone elaborate on using terragen w/Nuke in a linear 32bit workflow?

Thanks!

[nikita]

Did you disable soft clipping too?

[RArcher]

I can't elaborate on a Nuke workflow, but I can give a little clarification.  The gamma and contrast settings are not applied on a .exr image, it is strictly the raw data.  The renderview in Terragen does apply the gamma and contrast settings that you applied.

[Henry Blewer]

I used EXR in one of my images. I did color correction using Blender (It's the only EXR compatible program I have) I was hoping for DOF information to be included in the EXR image.

Well anyway, I'm sticking to bitmaps converted to png.

[Saurav]

Think of EXR files like the RAW files you get off cameras, they need processing.

[Oshyan]

Correct, the EXR output is unaltered by any of the "post effects" that would be added in the "Effects" tab. Note that TG2 applies some tone mapping ("soft clip") by default, and this is probably the effect most difficult to precisely reproduce (vs. the standard "Gamma"). However you should be able to get visually desirable results using an effective HDR image editor or compositor.

- Oshyan

[Henry Blewer]

Blender can handle EXR. It was my first attempt to use it's image processor. I barely touched the surface of what Blander can do for image processing.

[Matt]

The EXRs produced by Terragen are linear. The discrepancy between the Terragen viewer and the Nuke viewer  might be explained by the fact that Terragen's contrast, gamma and soft clip effects are only applied to its 8-bit images and in its viewer, while the saved EXRs contain only the unaltered linear data. I would expect that if you disable contrast and soft clip and keep gamma correction at the default 2.2, you should see a similar result as in Nuke if it is displaying with gamma 2.2 or sRGB.

Matt

[DutchDimension]

Resurrection time. 

Have you guys considered adding a small note inside the 'Tonemap' tab to inform TG users of this important distinction? Something like: 'Applies only to Terragen Viewer. Not to saved EXR renders'.

[Oshyan]

That's an interesting and potentially useful idea. I think we do have a very few other cases of similar in-UI warnings or notes. I'll look around and see if there is precedent.

- Oshyan

[digitalguru]

I haven't had a problem with .exrs from Terragen, but up until now have only rendered 16 bit .exrs to comp in Nuke, though I can't imagine there's any difference between those and 32 bit.

I don't have to touch anything in Terragen in the render settings or in Nuke if I'm using it at home - just render and view in Nuke with the sRGB (though I'll have a quick look tonight :-)

Is it possible you have a custom viewer  / lut in Nuke? The version of Nuke I'm looking at here at work has a standard sRGB / Gamma 2.4 - that might be different enough from Terragens gamma. Or if you are at work you might be viewing under a project LUT?

Terragen has a road map for including LUTs so might be easy to synchronise in the future.

32 bit is overkill for a beauty render though , 16 bit should be more than enough, though 32 bit is definitely the best format for data render elements like depth, position, normals etc.
Matt and Oyshan if you're reading would be great to have a switch to set these renders to 32 bit exr independently of the main beauty renders.

Think of EXR files like the RAW files you get off cameras, they need processing.

Not the same thing, RAW from a camera is just that, raw data that needs de-bayering to turn it into an image. Exr's are usually a linear image with no gamma correction, they can be viewed easily and just need the correct gamma to see them in the appropriate color space.

used EXR in one of my images. I did color correction using Blender (It's the only EXR compatible program I have) I was hoping for DOF information to be included in the EXR image.

Terragen doesn't do multi-channel exrs, you can render out a depth pass using render layers - https://www.youtube.com/watch?v=ihY_kp2rzxg

[ajcgi]

Terragen doesn't do multi-channel exrs, you can render out a depth pass using render layers

I hope Henry worked this out in the past 8 years some time.

[digitalguru]

ha ha - didn't look at the dates on that one!