Microsoft Office Tutorials and References
In Depth Information
Understanding Raster Graphics
In the rest of this chapter, we’ll be working mostly with raster graphics — in other words,
digital photos, like the ones you might take with your own digital camera or phone. A
raster graphic is made up of a very ﬁ ne grid of individual colored pixels (dots). The grid is
sometimes called a bitmap . Each pixel has a unique numeric value representing its color.
Figure 11.10 shows a close-up of a raster image. You can create raster graphics from scratch
with a “paint” program on a computer, but a more common way to acquire a raster graphic
is by using a scanner or digital camera as an input device.
A raster graphic, normal size (right) and zoomed in to show individual pixels (left)
The term bitmap is sometimes used to refer generically to any raster graphic, but it is also a specii c i le format for
raster graphics, with a .bmp i lename extension.
Because there are so many individual pixels and each one must be represented numerically,
raster graphics are much larger than vector graphics. They take longer to load into the PC’s
memory, take up more space when you store them as separate ﬁ les on disk, and make your
PowerPoint presentation ﬁ le much larger. You can compress a raster graphic so that it takes