By Chris Blair
Ok…so I stole the headline from the classic comedy film, Airplane, but I couldn’t resist. It’s the only quote I know that uses the word vector….as in vector graphics. I know, I know…they meant the aeronautic usage, but cut me some slack here.
There are basically two broad categories of graphic files used in design, vector graphics and bitmap graphics. Simple enough it seems. Yet I think many graphic artists were absent the day this was taught in college. Or worse, maybe they DON’T teach this in college. We repeatedly receive graphic files from other folks that are created or saved in the wrong format for their intended use.
So let’s clear the confusion up right now with a quick definition of the two primary types of graphic file formats.
Vector graphics are mathematical equations that when decoded by a computer, create an image. The primary advantage of vector graphics are they’re small in size and they can be infinitely scaled without image degradation.
This is possible because they’re simply text files using mathematical instructions. You can open many vector formats in a text editor and actually see the instructions in plain english. Of course it reads like jibberish, but it’s plain to see that the file is nothing more than a complex set of alphanumeric instructions.
Common file formats are .eps, .pdf, .ai, cdr, cgm, dxb and svg. Vector images are used primarily in computer illustration and CAD (computer aided design) programs, but as you can see from the extensions, even the ubiquitous PDF (portable document format) can be considered a vector graphic.
Bitmap graphics are actually tiny points of information that are displayed on a computer screen. They consist of grids with thousands of pixels or points of color, which when viewed as a whole, form the image. They are bit for-bit the same as what is displayed on screen, unlike a vector graphic, which can be sized up or down on that same screen with no change to the look or quality of the image.
Think of how an image is printed on paper. It’s comprised of thousands of tiny ink dots that form the image. Bitmap graphics are the electronic equivalent. For instance, digital photos are bitmaps. The advantage to bitmap graphics are they’re generally considered more photo-realistic than vector images. The disadvantage is they’re larger in file size and their resolution is limited. That means if you scale them larger than they were created, the image degrades noticeably. Scale them down, and depending on the algorithm used, they can artifact. Common bitmap formats are .tif, .tga, .gif. jpg, and .png.
But the confusion between vector and bitmap graphics gets more complex. Vector graphics can include bitmaps, and conversely, graphic artists often save bitmap graphics to vector formats. So a designer gets a logo as a .jpg file (a bitmap), opens it up in Adobe Illustrator (a vector graphic program), then saves it as an .eps file (a vector format). Unfortunately, this doesn’t magically convert the bitmap data to mathematical data. The file is STILL a bitmap in a vector graphic wrapper. But what happens is the resulting graphic is sent to another designer, who, believing it’s a vector graphic, scales it up to fit in his or her design. The result is a blurry, pixelated mess.
Now that your eyes and brain have gone cross, you’ve hopefully learned the difference between the two image types. Vector graphics are typically used for master files of logos, wordmarks, and layouts that will be scaled in subsequent designs, like print ads or billboards. Bitmap graphics are typically used for display graphics, like video, websites, and electronic signage. But there are hundreds of uses for both, and it’s perfectly ok to mix bitmap graphics into vector based layouts, as long as your bitmap file is of sufficient resolution (meaning the resolution is very high).
When I share a file with someone via email or FTP, I typically tell them everything I know about the file, including whether it’s a bitmap, vector or combination of the two.