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

[Sean Kennedy]

Ah, great idea! We could even set one up with RGB, one on each channel, and save it as a nodegroup.Thanks! So obvious, don't know why we didn't think of this. :)
I'm going to set one up today.
sean

> From: dnicolas at gmail.com
> Date: Fri, 23 May 2014 19:07:28 -0300
> To: bf-compositor at blender.org
> Subject: Re: [Bf-compositor] Clamping (Mix, Math, RGB Curves)
> 
> Hi all, I don't know how Blender's handles colors internally but
> wouldn't this work?
> http://www.pasteall.org/pic/show.php?id=71736
> (or are the V values already mapped to 0-1 from the separate node?)
> 
> Cheers,
> 
> 2014-05-23 18:46 GMT-03:00 Sean Kennedy <mack_dadd2 at hotmail.com>:
> > 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 tool
> > http://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 node
> > http://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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