[Bf-compositor] Clamping (Mix, Math, RGB Curves)

[Sean Kennedy]

Could we set the value of the clamp? It could come in as defaults of 1.0 and 0.0, but we could alter it to whatever we wanted. At R&H, most of the time we clamped brights around 14-16. We'd only turn it down under that if we got bad pixels when rendering.
If you had a superbright red, like R 12, G 3, B 4, and you put a clamp of 1 on it, obviously it's going to set each value to 1, so what was red now reads as white. But it would still be useful.
After Effects clamp toolhttp://cdn.aescripts.com/media/catalog/product/cache/1/image/800x600/040ec09b1e35df139433887a97daa66f/f/t/ft-clamp-ui_1.png
Nuke clamp is in the color grade nodehttp://docs.thefoundry.co.uk/nuke/63/pythondevguide/_images/getMinMax_01.png
I'm not posting the images to say "this is how we should do it", but rather, to say it is useful and professional compositors would indeed use it often.
In fact, I was working on a shot this week that could have used it. I was given stock footage from a client, and I have no idea how much they'll color correct it in post once I deliver the final vfx shot. SO I have to make sure all my blacks are in line with what is in the plate. I put a gamma on the plate just to view the black levels and see how they match up when pushed really far.https://dl.dropboxusercontent.com/u/10553822/clamp_blacks_01.jpg
Since we don't have a clamp, I ended up putting a mix node right after the stock footage node, setting it to Lighten, and making the color over it black. then I slowly raised it while watching until the blacks all came in line. Would have been much easier to sample the value of the darkest dark I wanted in the shot, throw a clamp node on with the black clamp set to those values.
In fact, at R&H, the Black Clamp node let you set an individual value for R, G, and B. And it had a color picker so you could just sample the image and the values would fill in automatically.
Anyway, just throwing out my $0.02. Obviously I've found a workaround and can live with it, but it would sure be great to someday see a clamp node.

Date: Fri, 23 May 2014 14:21:40 -0700
From: troy.sobotka at gmail.com
To: bf-compositor at blender.org
Subject: Re: [Bf-compositor] Clamping (Mix, Math, RGB Curves)



On May 23, 2014 1:56 PM, "Bartek Skorupa (priv)" <bartekskorupa at bartekskorupa.com> wrote:
> When I say: "clamp blacks" I always mean: set every value below 0.0 to 0.0.

> When I say: "clamp whites" I always mean: set every value above 1.0 to 1.0.

> Every compositing artist will know what I mean.
If we can generate a clamp / scale node, I am all for it.
I am saying there is no concept of white in a scene referred model, and as such, you have to be careful as to not write nodes that break the system.
It is that simple. No white. No brighter than white. So sorry, “Every artist...” is actually “Every artist unfamiliar with HDR work.”
So a clamp node _must_ not make the erroneous assumption that 1.0 means anything special, and rather provide for an arbitrary value range.
If this all seems like speaking an alien language, it is precisely why I chimed in and said “Whoa.”
There are already nodes that are broken because of erroneous assumptions. It would be a shame to make more.
With respect,

TJS



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