How many times have you tried to explain to your client why the logo from their website won't work on their trade show booth? If you're like me, the answer is about a bazillion. The next time you start blabbing on about the difference between raster vs. vector files (all while your client develops an über confused look on his face), just send 'em the link to this easy-to-understand article instead.
Raster Graphics
Overview
A raster graphic is an image made of hundreds (or thousands or millions) of tiny squares of color information, referred to as either pixels or dots. (
Technically pixels refer to color blocks viewed on an electronic monitor where as dots refer to the ink dots on a printed piece. But even professional designers, myself indluced, often use these two terms interchangeably.)
The most common type of raster graphic? A photograph. The designer's preferred program for creating and editing raster files? You guessed it: Adobe Photoshop.
Popular raster file format extensions include: jpg/jpeg, psd, png, tiff, bmp and gif.
Pros of Raster Images
- Rich Detail: Ever wondered what the term "dpi" stands for? It means "dots per inch," a measurement of how much detailed color information a raster image contains. Say you've got a 1" x 1" square image at 300 dpi—that's 300 individual squares of color that provide precise shading and detail in your photograph. The more dpi your image contains, the more subtle details will be noticeable.
- Precise Editing: All of those individual pixels of color information can also be modified, one by one. So if you're a true perfectionist, the level of editing and customization available in a raster image is almost limitless.
Cons of Raster Images
- Blurry When Enlarged: The biggest downfall to raster images is that they become pixelated (aka grainy) when enlarged. Why is this? Well, there are a finite number of pixels in all raster images; when you enlarge a photo, the computer takes its best guess as to what specific colors should fill in the gaps. This interpolation of data causes the image to appear blurry since the computer has no way of knowing the exact shade of colors that should be inserted.
- Large File Size: Remember how a 1" x 1" square at 300 dpi will have 300 individual points of color information for the computer to remember? Well let's say you have an 18" x 24" photo— that's 129,600 bits o' info for a computer to process which can quickly slow down even the faster machine.
Vector Graphics
Overview
A vector graphic uses math to draw shapes using points, lines and curves. So whereas a raster image of a 1" x 1" square at 300 dpi will have 300 individuals pieces of information, a vector image will only contain four points, one for each corner; the computer will uses math to "connect the dots" and fill in all of the missing information.
The most common types of vector graphics? Fonts and logos. The designer's preferred program for creating and editing vector files? Adobe Illustrator.
Popular vector file format extensions include: eps, ai and pdf.
Pros of Vector Images
- Infinitely Scalable: Through the wonders of math (which I don't claim to understand), vector files can be scaled up or down as much as you want without losing any image quality. Whereas a raster image must guess the colors of missing pixels when sizing up, a vector image simply uses the original mathematic equation to create a consistent shape every time.
- Smaller File Size: Using our previous 1" x 1" square example, a vector file needs only four points of data to recreate a square versus 300 individual pixels for a raster image. For simple graphics, like geometric shapes or typography, this means a much smaller file size and faster processing speed.
- Edibility: Unlike popular raster-based formats, such as a jpg or png, vector files are not "flattened." When you open 'em back up in a program such as Adobe Illustrator, all of the original shapes exist separately on different layers; this means you can modify individual elements without affecting other objects in the image.
Cons of Vector Images
- Limited Details: Because of the mathematically way that a vector remembers data, they are not practical for complex images that require exact coloring. Sure, you can create basic color gradients, but you'll never be able to match the color detail available in a raster image where each individual pixel can be its own individual shade.
- Limited Effects: By definition, vector graphics are created from simple points and lines. This means they can't handle certain styling effects, like blurring or a drop shadow, that are available with raster images.
Raster in Illustrator? Vector in Photoshop? What?
Yes, you read that right. While Adobe Illustrator is primarily a vector-based program, it has some raster-only elements available, such as drop shadows or outer glows. Likewise, Adobe Photoshop now allows you to work with vector-based objects (called smart objects) within the traditionally raster-based program. Don't be confused…this added flexibility within design programs still doesn't override the traditional wisdom:
Raster = photographs = great color detail, but can't enlarge without becoming blurry.
Vector = fonts/logos = ability to enlarge without losing quality, but limited color detail
