View Full Version : Nuke, EXR, sRGB, passes

07 July 2010, 12:57 AM
Hi, noob here(to nuke). So I'm importing an EXR render from max into nuke. I've created a node setup where all the passes(channels) are added to create the final image. and the final image is exactly like the full beauty render(rgba). My problem is that when I change the image colorspace to sRGB, only the full rgba image changes, but now the passes that create the full image still looks like it's in linear workflow(higher gamma)... My question is how do I apply sRGB to all the rest of the channels so the comping ends up looking like the sRGB image. Thanks! :thumbsup:

07 July 2010, 01:13 AM

07 July 2010, 04:32 AM
How are you changing the images color space back to sRGB (via a write node, adding a LUT, changing the color space setting on the read node)?

07 July 2010, 06:51 AM
I'm doing it through the image read that not right? :shrug:

When I import the image the default is linear: default(linear)..

and It's set on srgb on the viewer...

LUT already has everything on sRGB

07 July 2010, 04:47 PM
The colorspace knob in the Read node will only affect your rgba layer. If you need/want to convert them all, set your Read node to "Raw Data" and convert all layers with a Colorspace node.

However, why do you want to do this conversion first as opposed to at render time?

07 July 2010, 04:57 PM
You want to work in linear but then you can write it out to a file in sRGB colorspace at the end. So don't change the read node.

07 July 2010, 05:35 PM
thanks for the replies guys...

I'm trying to see it in sRGB format because Linear workflow has more gamma.. so if I were to color correct the images in nuke and then convert to sRGB at the end, then it'll make the final video darker again, which will kinda defeat the purpose of color correction...?? that's how I see it anyway... how do I know what the final result will look like if the final image will have a different gamma rate?

07 July 2010, 02:55 AM
I think you have some misunderstandings about Nuke's internal color processing, and some greater issues with colorspaces themselves.

Nuke linearizes every image you read in. When you read in a file, the "colorspace" setting on the Read node is telling Nuke what to convert FROM to get the file's data into linear light space, not what to convert it to.

Inside of Nuke, all pixel operations are performed in the same linear space. However, since the vast majority of monitors in use today are calibrated or have a preset for displaying images in sRGB space, the linear data present in Nuke will LOOK incorrect in its raw form.

The solution to this is the vLUT (Viewer Look-Up Table). This performs what is essentially an isolated conversion of the data in the viewer into whatever colorspace is selected. This is the dropdown you see in Nuke's viewer window that says 'sRGB' by default. The important thing to note here is that this is not actually changing the image at all, but essentially putting a "filter" between you and your image data so you can view it correctly.

When you write a file out, you want to write it to the colorspace that will look correct. This is where the 'colorspace' knob on the Write node comes into play. To greatly simplify things, the most "common" image formats are written in sRGB space (JPEG, TIF, TGA, BMP, PNG). EXR files are most commonly written in linear space (a.k.a. 1.0 gamma), though they don't have to be. DPX files can be linear, sRGB, LOG, etc.

So to summarize, the term "linear workflow" has nothing to do with the output file, and is really an outdated/unnecessary term in Nuke (since EVERYTHING is done in linear space). It's more important if you're dealing with programs that allow you to work in various colorspaces (AE, Fusion), or if you're dealing with 3D lighting and rendering. When you write images out of Nuke, the colorspace you write them to will almost certainly be determined by what format you're writing to and nothing else.

07 July 2010, 06:47 AM
Wow, very nice breakdown. thank! hmm.. think I get it now.. So basically when I import an EXR, I should keep the read file as linear(which it is by default), and view it as sRGB(viewerprocess) to see how the final will look, and eventually export it using a file format that fits that sRGB format..? I think I'm getting this now lol , sorry, I'm a modeler/texturer. This is all new to me.

Thanks again!

07 July 2010, 07:36 AM
Yep. Sounds like you have the hang of it now!

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