Image Acquisitionand Proces

Image Types and File Management 3
FIGURE 1.2 Image data represented as a surface plot.
Increasing the bit depth of the image to 16 bits also increases the amount of memory
required to store the image in a raw format:
MemoryRequired = 1024 ¥ 768 ¥ 16
= 12582912Bits
= 1572864Bytes
= 1.536MBytes
You should therefore select an image depth that corresponds to the next-highest level
above the level required, e.g., if you need to use a 7-bit image, select 8 bits, but not 16 bits.
Images with bit depths that do not correspond to those listed in the previous
table (e.g., 1, 2 and 4-bit images) are converted to the next-highest acceptable bit
depths when they are initially loaded.
1.1.2 COLOR
Color images are represented using either the Red-Green-Blue (RGB) or Hue-
Saturation-Luminance (HSL) models. The Vision Toolkit accepts 32-bit color images
that use either of these models, as four 8-bit channels:
Color
Model
Pixel Depth
Channel Intensity
Extremities
RGB a Red Green Blue 0 to 255
HSL a Hue Saturation Luminance 0 to 255
The alpha (a) component describes the opacity of an image, with zero representing
a clear pixel and 255 representing a fully opaque pixel. This enables an
image to be rendered over another image, with some of the underlying image
showing through. When combining images, alpha-based pixel formats have several
advantages over color-keyed formats, including support for shapes with soft or