May be old news to some, but I found some useful nodes today…
Math Node: Round
makes Posterising easy
Vector: Map Value
Slice the value of an image (clip the values top and bottom and remap if you want).
Math Node: Minimum/Maximum
Make a video legaliser (clip values to 0%IRE and 100%IRE)
I’ve used them but not in this context.
Any blend files or screenshots would be welcome.
Here is the posterise effect using the Math Node “round”.
Very last century, but may be useful for color reduction, cartoon effect or half tone simulation.
Posterise nodes.blend (658 KB)
And here is the clipping with Map Value node (just on luma but you could split channels again).
I realise that last one can be done with curves but it’s cool anyway 
I made a video legaliser that hard clips (yuck) to 100%IRE and 0%IRE. It should be a last step before output, to catch excursions outside legal color space.
You can see on the waveform from the Split Viewer, that I have used a Brightness and Contrast node to push the values into illegal color space (right). On the left shows the results of the clip function.
In this screen you can see that I have added a Less Than node and overlayed it to act as a Clip warning. So you know where the clipper is having effect.
You can use the curves tool to do this but you can’t enter a value to drive the curve. Also I think the curve tool works with a normalised value of the input image. So it can have a different result for each source, not helpfull for garunteeing clip to a set value.
Legaliser nodes.blend (683 KB)
Heres another application, restoring burnt out highlights from another channel.
In this shot the sky has blown out the blue channel (it is clipped). So I have chosen the red channel, isolated the peaks without stretching them then matted them over the blue channel peaks.
Wow, that’s awesome! Thanks for sharing! 
Very nice, 3point! Do you happen to know if it’s possible to create a High/Low pass filter using the nodes? I did some “research” before, but couldn’t find anything applicable to Blender.
Sebastian, its quite productive being bored at work.
I must have missed it. I will give it a go in while. Thanks!
