Apple Shake 4 - Manual (Page 411)

Chapter 15 Image Processing Basics 411
Note: In 8-bit images there is no 50 percent point—you have a smidgen less than 50
percent gray and a smidgen more than 50 percent, but you cannot get an exact 50
percent value. This occasionally becomes an issue when creating and using macros.
If this is the case, then why not always work at 16-bit resolution? Most film houses do,
but it comes at the expense of slower calculations, more memory required, and larger-
sized image files requiring significantly more hard disk space.
Float
The Shake 32-bit representation is “float”—values can go above 1 or below 0. In all of
the above examples, the ramp ranges from 0 to 1. If you add two 8-bit ramps together,
the white values are added together (1+1), but clipped at 1. This is fine visually, but you
may later do other mathematical computations in which it is important to realize that
1+1 is 2, not 1. A good example is the Z channel, which is always in float. The Z channel
is usually generated by a 3D render, and supplies the distance on a per-pixel basis from
the object to the “camera.” Therefore, values could go from 0 to infinity. If you swap
your Z channel into your red channel, you do not want it clipped off at 1, because you
could not tell the difference between the pixels that are 2 units away and the pixels
that are 1000 units away. A float representation, however, maintains these values.
Bit Depth Independence
Shake recognizes and maintains the bit depth of incoming images—except for 10-bit
Cineon files, which are automatically boosted to 16 bits. Because Shake concatenates
color corrections, in Shake you are penalized less frequently when working at 8 bits
than you are in other software. This is because adjacent color corrections are collapsed
into a single mathematical lookup table, enabling Shake to perform the overall
computation in float. The resulting image is returned to its source bit depth.
With the use of the Bytes node, you have the option of modifying your image to a
higher or lower bit depth. As the name implies, the Bytes node takes bytes as its
argument, so a value of 1 equals 8 bits, 2 equals 16 bits, and 4 equals 32 bits (or float).
(There is no “3 bytes” setting.) For information on the Bytes node, see “
The Bytes Node ”
on page 413.