Apple MA434Z/A User Manual - Page 648

Expressions can use the following variables: • The variables r, g, b, a, and z refer to the value of the original channels (red, green, blue, alpha, and Z). • The variables x and y are the coordinates of the pixel. • The variables width and height are the width and height of the image. • The variable time is the current frame number (time). Many operators can be represented by an arithmetic expression, such as reordering, color correction, and gradient generation, or even circle drawing. Note that no spaces are allowed in the expressions, unless you can use quotes for more explicit grouping. Task Reordering Red correction Red and blue correction Same expression for red, green, and blue X gradient in matte Y gradient in matte Blue spill removal Random noise Turbulent noise (1 channel) Clip alpha if Z is less than 20 Clip alpha if Z is more than 50 A smooth alpha gradient from Z units 1 to 70 Example: Each value field can be filled independently in the interface-these are all command-line examples. shake bg.iff -colorx b r a g shake bg.iff -colorx "r*1.2" shake bg.iff -colorx "r*1.2" g "b*1.5" shake bg.iff -colorx "(r+g+b)/3" -reorder rrr shake -colorx r g b "x/width" shake -colorx r g b "y/height" shake primatte/woman.iff -colorx r g "b>g?g:b" shake -colorx rnd(x*y) rnd(2*x*y) rnd(3*x*y) shake -colorx turbulence2d(x,y,20,20) shake uboat.iff -colorx r g b "z50" shake uboat.iff -colorx r g b "(z-1)/70" LogLin The LogLin node is typically used to handle logarithmic film plates, such as Cineon files from a film scanner, or when writing files out for film recording. It converts the images from the logarithmic color space to the linear color space for accurate compositing. You can then use the node at the end of your node tree to convert the images back into logarithmic space for film scanning. You can also use this around nodes that only work in 8 or 16 bits, functions such as Primatte, Keylight, or other plug-ins from third parties. Ultimatte is the exception, as it maintains float values. For a full description of this process, see "The Logarithmic Cineon File" on page 437. The LogLin color parameters are linked together by default, so gBlack and bBlack reflect the rBlack value. You can of course adjust these to further color correct your scanned plates. 648 Chapter 23 Color Correction