Graphics Programs Reference
In-Depth Information
Bitmap
A bitmap image uses only one of two color
values—black or white (no gray)—to represent
the pixel data. These 1-bit images have a very
small file size. To create a bitmap, you first must
convert the image to an 8-bit grayscale formula,
and then convert to the Bitmap image mode. Do
not confuse Bitmap mode with a bitmap image,
which is another name for
raster
(or pixel-based)
images. Additionally, avoid confusion with the
BMP file format, which is a standard Windows
file format that dates back to the earliest ver-
sion of Windows. An image in the Bitmap mode
simply uses only black and white to represent
image data.
Indexed Color
Indexed Color mode severely limits the number
of colors used to represent an image. In Indexed
Color mode, up to 256 colors are available. To
reduce file sizes (and download times), some
web designers use fewer colors in their graphics.
They will turn to specialized formats like GIF
and PNG-8. Although this mode reduces file size,
it also visibly lowers the quality of the image.
Indexed Color mode works well for illustrations
or logos but not so well for photos on the Inter-
net. Instead of converting your original image
to Indexed Color mode via the Image menu,
use the Save For Web command (File > Save
For Web). This will convert the file to a GIF or
PNG-8 (both use the Indexed Color mode), but
leave the original image in its original mode.
