• Bitmap images are made up of dots, known as
• They contain a fixed number of pixels and
each pixel has a specific location and colour.
• Can represent subtle grades of shades and
• Because of the fixed number of pixels, they
can lose detail when made larger and can look
jagged if printed at too low a resolution.
Bitmap images are resolution dependent.
Resolution refers to the number of pixels in an image
and is usually stated as dpi (dots per inch)
or ppi (pixels per inch)
Bitmap images are displayed on your computer screen
at screen resolution: approximately 100 ppi.
However, when printing bitmaps, your printer needs
much more image data than a monitor. In order to
render a bitmap image accurately, the typical desktop
printer needs 150-300 ppi.
• Common bitmap formats include:
• JPEG, JPG
• PICT (Macintosh)
• PSD (Adobe Photoshop)
• Popular bitmap editing programs are:
• Microsoft Paint
• Adobe Photoshop
• Corel Photo-Paint
• Corel Paint Shop Pro
• The GIMP
Bitmap images in general do not inherently
support transparency. A couple of specific
formats--namely GIF and PNG--support
transparency. In addition, most image editing
programs support transparency, but only
when the image is saved in the software
program's default format.
• A common misconception is that the
transparent areas in an image will remain
transparent when an image is saved to
another format or copied and pasted into
• GIF - GIF is the original format with transparency
support for the Web.
• The problem with GIF is that it reduces the color
palette to no more than 256 colors, causing color
shifts, posterization, and distortion in high color
images such as photographs.
• Another downside to GIF is that it only supports
1-bit transparency, meaning you can't have areas
of partial transparency. Each pixel is either
completely transparent or not, so you cannot do
things like smooth drop shadows that fade away
• PNG - PNG is a newer format developed to
overcome many of the limitations of GIF. It
supports high color and partial transparency
using alpha channels. Although PNG has been
around for a while now, the biggest problem with
it is that many people are still using older
browsers that do not support PNG, and even
some modern browsers do not support all the
features of PNG. For instance, Microsoft Internet
Explorer 6, which is still in wide use today, does
not support alpha transparency of PNG images.
Transparent PNG images do display properly in
An alpha channel is a special type of channel
used in graphics software for saving
Most bitmap editing software allows you to
save multiple alpha channels with an image
when it is saved in the program's native file
format. Any of the alpha channels can be
reloaded as a selection or mask at any time,
even after closing and reopening the image.
Open this table from the portal – complete it and save in Unit 18 Folder
Standard Windows based image format
– very large memory usage!