Color Correction - Nuke 101: Professional Compositing and Visual Effects - page 148

Understanding Nuke's Approach to Color
Nuke is a 32-bit float linear color compositing application. A bit of a fancy description
there, with potentially new words. I explain this bit by bit:
• 32-bit: That'stheamountofbitsusedtoholdcolors.Mostcompositingandimage-
manipulation programs are 8-bit, allowing for 256 variations of color per channel
(resulting in what's referred to as “million of colors” when combining the three
color channels). This is normally fine for displaying color, but is not good enough
for some calculations of operations, and may result in unwanted results such as
banding —inaccurate display of gradients where changes in color happen abruptly
insteadofsmoothly.32-bitallowsforawhopping4,294,967,296variationsofcol-
or per channel. That's a staggering amount that results in much more accurate dis-
play of images and calculations of operations. 8- or 16-bit images brought into
Nuke will be bumped up to 32-bit, although that doesn't add any detail, it just en-
ables better calculations from that point onwards.
• Float: Normally the color of an image is represented between black and white.
In 8-bit images, for example, the 256 color variations are split evenly between
black and white—so the value 1 is black, the value 256 is white, and the value
128 is a middle gray. But what about colors that are brighter than white? Surely
the whiteness in the middle of a lit light bulb is brighter than a white piece of
paper? For that reason, there are colors that are brighter than white called super-
whites.Therearealsocolorsthataredarkerthanblackcalledsub-blacks(butthere
isn't a real-world analogy that can be used here short of black holes). Using 8 bits
to describe an image simply doesn't allow enough room to describe colors bey-
ond black and white. These colors get clipped and are simply represented as black
or white. However, in 32-bit color, there is plenty of room and these colors be-
come representable. As mentioned before, 8-bit color is normally enough to dis-
play images on-screen. Furthermore, the computer monitor can still display only
white—and nothing brighter. However it is still very important to have access to
those colors beyond white, especially when color correcting. Darkening an image
that has both a piece of white paper and a light bulb in it will leave the light bulb
white, while darkening the paper to a gray color results in an image that mimics
real-world behavior and looks good and believable. Doing the same with a non-
floating image will result in the white paper and the light bulb looking the same
gray color—which will be unconvincing.
• Linear: Linearcanmeanlotsofthings.Intermsofcolor,Imean linear color space .
A computer monitor doesn't show an image as the image appears in reality, be-
causethemonitorisnota linear displaydevice.Ithasamathematical curvecalled