A raster file (bitmap) is an image made of hundreds, thousands and even millions of tiny little squares of color, these little squares are referred to as either pixels or dots. now if we are getting technical, pixels are color blocks that are viewed on an electronic monitor where as dots are the actual dots of ink printed or, in this case, the laser beam. But we often use these two terms interchangeably.
The most common type of raster image is a photograph.
The most popular raster file formats are: jpg/jpeg, psd, png, tiff, bmp and gif.
Pros of a Raster Image:
- High/Rich Detail: Have you ever wondered what the term “dpi” stands for? It means “dots per inch,” its a measurement of how much detailed color information a raster image contains. Lets say you’ve got a 1” x 1” square image at 300 dpi, that’s 300 individual tiny squares of color that provide precise shading and detail in your image. The higher the dpi of your image, the more subtle details will be noticeable.
- Precise Editing: All of those tiny individual pixels of color information can 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 a Raster Image:
- Blurry When Enlarged: The greatest downfall to raster images is that they become pixelated (grainy, dotty) when enlarged. Why? Well, there are a limited number of pixels in all raster images; when you enlarge an image, the computer makes its best guess as to what specific colors should fill in the gaps. This interpolation of data causes the image to appear blurry or pixelated since the computer has no way of knowing what the exact shade of color that should be inserted to fill the gaps.
- Large File Size: Remember that a 1” x 1” square at 300 dpi will have 300 individual points of color information for the computer to remember! Now let’s say you have an 18” x 24” image – that’s 129,600 bits of color information for a computer to process which can quickly slow down even the fastest computer.
A vector image 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 individual pieces of information, a vector image will only contain four points, one for each corner; the computer will then use math to connect the dots and fill in all of the missing information.
The most popular vector file format extensions include: eps, ai, svg and pdf.
Pros of a Vector Image:
- 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 them 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 a Vector Image:
- Limited Details: Because of the mathematical way that a vector remembers data, they are not practical for complex images that require exact coloring. Yes, 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.