Datasheet

14 Chapter 1: Introduction to Computer Graphics and 3D
COLOR DEPTH
An image file stores the color of each pixel as three values representing red, green, and
blue. Image type depends on how much storage is allotted to each pixel (the color depth).
These are the color depths common to image files in CG production:
Grayscale The image is black and white with varying degrees of gray in between, typically
256 shades of gray. Grayscale images are good for rendering out black-and-white subjects
as well as being used for some types of texture maps like displacement maps.
8-Bit Image File (a.k.a. 24-Bit Color Display) Referred to as 24-bit color display or True
Color in desktop settings for Windows, each color channel is given 8 bits for a range of
256 shades of each red, green, and blue channel, for a total of 16 million colors in the
image. This color depth gives good color quality for an image and is widely used in most
animation applications. Most of your renders from Maya will probably be as 8-bit image
files, because most monitors are only capable of 8-bit color reproduction in playback.
16-Bit Image File Used in television and film work using such file types as TIFF16, a 16-bit
image file holds 16 bits of information for each color channel, resulting in an impressive
number of color levels and ranges. Each file can exceed several megabytes even at low
resolutions. These files are primarily used in professional productions, although they’re
being supplanted by the use of 32-bit images.
32-Bit Image File This is where the big kids play. Used primarily for film work but increas-
ingly in general use, 32-bit image files, such as the OpenEXR format, give you an incred-
ible amount of range in each color channel. This lets you adjust a wide range of tones and
hues in your rendered output for the fullest detail. They’re pretty much standard for film
work because outputting CG to film can require high levels of color and brightness range
in the image.
High Dynamic Range Imagery (HDRI) HDRI images are 32-bit float images that are created
by combining several digital photos into one image file. For example, photos are taken
of a subject with different levels of light using various exposures during photography.
With a “32-bit float” file format, a lot of information can be stored about the colors in the
image—that is, a very high bit depth is achieved. This way, you have a series of images
that range from dark (with very fast exposure) to normal (with proper exposure time) to
blown-out brightness (with overexposure). These different exposures are then compiled
into a single HDR file format (.hdr) that represents a wider range of light and dark than a
typical photo. These files are traditionally used as lighting setups, especially for scenes in
which CG is integrated with a live-action background using image-based lighting (IBL), a
concept we’ll touch on in Chapter 11.
COLOR CHANNELS
As mentioned, each image file holds the color information in channels. All color images
have red, green, and blue color channels that, when viewed together, give a color image.
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