Vector vs. Bitmap Images Explained
First
off, we’ll have a quick look at what exactly a vector file and a bitmap file
are.
Vector:
A vector file is a file
that’s constructed from shapes that are defined by mathematical equations. Because
they're scalable, vector-based images are resolution independent. You can
increase and decrease the size of vector images to any degree and your lines
will remain crisp and sharp, both on screen and in print. See images below.
The
fact that vectors are constructed using mathematical equations is their
strength. It keeps the details in the image as high as possible, and means that
if you want to change how large or how small you would like the image to be
printed, you can do so without worrying about quality.
Another advantage of
vector images is that they're not restricted to a rectangular shape like
bitmaps. Vector objects can be placed over other objects, and the object below
will show through. A vector circle and bitmap circle appear to be exactly the
same when seen on a white background, but when you place the bitmap circle over
another color, it has a rectangular box around it from the white pixels in the
image.
Vector blown up vs. Bitmap blown up
Bitmap:
A bitmap file
(also known as a raster)
is an image that’s constructed from pixels. If you zoom into a bitmap file, you
start to see the individual pixels and, consequently, it’s important that
bitmap files for of printing are used with a resolution that is high enough —
typically, 300 dpi
or more.
A strength of bitmaps is linked with their use in photography. Photos are created as bitmaps within a typical digital
camera, normally as JPGs or RAW files. So if you’re working with
photographic-quality images, you’ll typically need to use a bitmap file.
Because bitmaps are
resolution dependent, it's impossible to increase or decrease their size
without sacrificing a degree of image quality. When you reduce the size of a
bitmap image through your software's resample or resize option,
pixels must be discarded.
When you increase the
size of a bitmap image, the software has to create new pixels. When creating
pixels, the software has to estimate the color values of the new pixels based
on the surrounding pixels. This process is called interpolation.
Let's assume you have
a red pixel and a blue pixel beside each other. If you double the resolution
you will be adding two pixels between them. What color will those new pixels
be? Interpolation is the decision process that determines which color those
added pixels will be; the computer is adding what it thinks are the correct
colors.
Scaling an image does
not affect the image permanently. In other words, it doesn't change the
number of pixels in the image. What it does is make them bigger.