Tag: color grading

Premult = multiplies the input’s rgb channels by its alpha

Keymix = similar to Merge but accepts unpremult assett. Often used for merging masks

Uses of Premult node:
– Merging unpremult images = to avoid unwanted artifacts (fringing around masked objects)
– Color correcting premultiplied images.Unpremult → color correction → premult

Unpremult = divides the input’s rgb channels by its alpha

Colour correcting premultiplied images:

When you colour correct a premultiplied image, you should first connect an Unpremult node to the image to turn the image into an unpremultiplied one.
Then, perform the colour correction. Finally, add a Premult node to return the image to its original premultiplied state for Merge operations. Typically, most 3D rendered images are premultiplied.
** If the background is black or even just very dark, the image may be premultiplied.

Merging Operation Examples:

Reformat = lets you resize and reposition your image sequences to a different format (width and height).
– Allows you to use plates of varying image resolution on a single script without running into issues when combining them.
– All scripts should include Reformat nodes after each Read node to specify the output resolution of the images in the script.

Colorspace and Linearization
– Colorspace defines how the footage was captured or exported. Most files are non-linear, and knowing the correct colorspace is critical for proper linearization.
– Linearization is the process of converting footage into linear space. All the tools inside nuke are built around linear math. This also allows the mixing of media types. We need to know what colorspace of the file was before starting to work on the file.
– You can work in LOG/RAW or Linear.

LUTs, CDLs, and Grades
· LUTs can be used for creatively or technically, i.e. converting from log to lin, or adding a “look”
· CDLs are creative, i.e. adding a “look” to a clip
· Graded footage means colored to it’s “final” look

For color correction we always want to think in terms of:
– Highlights
– Midtones
– Shadows
Two commonly used nodes are : grade & colorcorrect

– To grade Highlights we use either GAIN or MULTIPLY,
– To grade Shadows we use LIFT
– To grade Midtones we use GAMMA.

How to match color using grade node to match constant A to constant B
– Add a grade node (G), pick constant A color as WHITEPOINT by selecting eyedrop -> ctrl + shift on constant A color. 
– Pick constant B as GAIN by selecting eyedrop -> ctrl + shift on constant B

Note: Cloning a node will keep the same value/setting across the nodes (signified by a C letter on top of the node)