Nancy Michon's Blog

What the heck is this vector-raster thing, anyway? Just hearing the words vector and raster can make anyone's eyes glaze over, so here's as brief an explanation as I'm capable of writing.

There are two basic types of computer graphics files:

Paint (Raster/Bitmap) - Paint programs work with pixels, are referred to as raster- or bitmap-based, and are best used for images where subtle gradations of shades and colors are desired, such as photographs. (For purposes of this discussion, pixels = dots.)

Drawing (Vector) - Drawing programs work with vectors, and are great for graphic, crisp-edged object images, such as logos, typefaces, charts and graphs, or any image that must have sharp lines when scaled to various sizes.

PAINT (resolution-dependent)

Most of us have heard of pixels. They are tiny boxes or dots filled with color, and you can roughly equate them to the dots you see when you look close up at a color newspaper photo. All those tiny boxes or dots are small enough to blend together when you look at the image, and you perceive the many hues and shades that make up the image without noticing the individual dots.

When using a paint program such as Photoshop, the quality of your image depends on the amount of pixels in each square inch, which is called it's resolution. Images meant for viewing on computer screens have 72 pixels per inch, which is the maximum resolution of the monitor. Offset printing requires 300 dots per inch. Newspaper and digital printing both require something in the middle, from 120-220 dots per inch.

If there are too few pixels per inch, the image will look fuzzy. If there are enough pixels per inch, it will look great. The amount of pixels in a paint image is fixed. If you enlarge an image that has enough pixels to begin with, the pixels get larger, and the image gets fuzzier, or 'pixelated', and you might even start to see the boxes. Curved edges will start to look jagged, and the finer details will be lost.

If this were to happen to your image, it would be bad. Very bad. Embarrassing, actually. But it would simply put you in a position of solidarity with millions of others who have also made this mistake. It's only human.

A common misconception among these millions is that it's possible to get very clear, crisp results when printing a project using art copied off of a web page. Remember that 72-pixels-per-inch rule for computer monitors? If you take a one-inch-wide logo from a web page and print it six inches wide on a printed piece, the logo will look very boxy and jagged.

But take heart. There are other ways to get great results in your printed pieces, and in any project for which raster-based art is not recommended. Read on.

DRAWING (resolution-independent)

In consideration of any mathphobes out there (of which I'm one), fair warning - I have to mention math here, but only a little, I promise. Vector graphics are images made up of mathematical formulae that define the lines, shapes and colors of your image when created in a drawing program such as Illustrator. You tell the program where to put a box, a circle, or other object, what color it will be and how large, and the program calculates the boundaries of the object using math. Word processing programs use vectors to display fonts, so you've likely already used vectors if you've enlarged the text on a page.

When you edit a vector object by enlarging it, the program recalculates the math and places the boundaries of the object where you want them. On a computer screen, this means that the tiny dots always stay tiny. It's just the location of the dots that make up the boundaries that changes, based on the math. This way, you can enlarge your image without loosing the fine details, crisp edges or smooth curves.

This is the reason, and I can't emphasize this enough, that it's important to get your mitts on a copy of the original vector file of your company's logo and keep it in a safe place, perhaps a vault in upper Siberia. And make sure that the people who need it are able to access it without erasing the original. Treat this file as the valuable piece of business property that it is, or you will one day regret it. Why? Because you'll be asking someone like me to recreate it, and you'll either a) incur additional costs, or b) enter into questionable legal territory if you don't have permission to use said logo.

A Confusing Caveat

Some files may contain both raster and vector images. For example, this can happen if a photographic raster image is placed in a drawing program's file. In this example, if you try to enlarge the resulting file, the vector elements will scale up just fine, but the raster image may not, depending on it's original resolution (or pixels per inch). As long as your file is built to the same size you need for your final result, whether a web page or a large format poster or something in between, AND your resolution matches same, you're fine!

Resources, or Huh?

In case you're still scratching your head, or you find this topic so fascinating that you just have to read more, these links may be helpful:

Shop Talk - all about vectors and bitmaps

Understanding Bitmaps and Vectors

Bitmap and Vector Graphics Explained

Till next time! --Xena, er, I mean Nancy