Introduction: Bits Per Pixel and Related Ideas
The terminology for image formats can be confusing because
there are often several ways of describing the same format. This topic explains
what the terms mean.
If an image is 24 bits per pixel, it is also called a 24-bit
image, a true color image, or a 16M color image. Sixteen million is roughly
the number of different colors that can be represented by 24 bits, where there
are 8 bits for each of the red, green, and blue (RGB) values.
A 32-bit image is a specialized true-color format used in image
files, where the extra byte carries information that is either converted or
ignored when the file is loaded. The extra byte is used for an additional
color plane in CMYK files, which are specialized files for color printing.
In that case, LEADTOOLS, by default, converts the values to 24-bit RGB values
when loading the image. The additional byte may also be used for an Alpha
channel, which carries extra information such as a transparency indicator.
If an image is 16 bits per pixel, it is also called a 16-bit
image, a high color image, or a 32K color image. Thirty-two thousand is roughly
the number of different colors that can be represented by 16 bits, where there
are 5 bits for each of the red, green, and blue values. (Devices that specify
64K color support are also referring to 16-bit images, but they are counting
the left-over bit.)
If an image is 8 bits per pixel, it is also called an 8-bit
image or a 256-color image. Two hundred fifty-six is the number of different
colors that can be achieved by using the image data as 8-bit indexes to an
array of colors called a palette.
If an image is 4 bits per pixel, it is also called a 4-bit
image or a 16-color image. Sixteen is the number of different colors that
can be achieved by using the image data as 4-bit indexes to a palette.
If an image is 1 bit per pixel, it is also called a 1-bit image,
a black and white image, a 2-color image, or a bitonal image. Two is the number
of different colors that can be achieved by using the image data as 1-bit
indexes to a palette. The palette can contain colors other than black and
white, although black and white are most common.
If an image is grayscale, its red, green, and blue values are
all the same, and the values are incremented from the lowest to the highest.
For example, an 8-bit grayscale image has 256 shades of gray, with values
from 0 to 255.
LEADTOOLS SDKs allow developers to add extensive color
conversion support to their applications quickly and easily. LEADTOOLS can
convert images from any
color resolution to any other color resolution, from 1-bit to 64-bit,
with multiple dithering methods using various palette options . Additionally,
LEADTOOLS supports 4, 8, 12, and 16-bit grayscale. Support for 64 bit color
and the 12 and 16-bit grayscale images is only available in the LEADTOOLS Document/Medical Developer Toolkits.