Have you ever sent a logo file or other image file to a designer or printer only to be told it can’t be used because it’s “bit-mapped”? A “vector” file is needed instead. What are they talking about?
Bit-Map vs. Vector Images
- All digital images are either bit-mapped or vector files. What is the difference? Think of bit-mapped (or raster) graphics as an image where each pixel of the image is equal to a tile in a mosaic or an embroidered cross-stitch. If you stand back or squint your eyes, the individual elements come together to form a picture. But as you move closer, you begin to notice the pieces that make up the whole.
- The same principle applies with a bit-mapped graphic…the more you enlarge it, the fuzzier it appears because you are starting to see the individual pixels that make up the image.
On the other hand, vector (or object-oriented) graphics are based on mathematical equations of points and paths to represent them in computer files. Since the art is created using lines and curves, it will reproduce as crisply on a business card as it will on a billboard. Think of an ink drawing-no matter how close you get, the lines are still crisp and smooth.
- If it the difference still isn’t clear, spend three minutes watching this informative and amusing video, Pixels vs. Vectors, on MacMercTV. A picture (or in this case, a video) is worth a thousand words!
Tips to Recognizing Image File Types
Now that we’ve defined the difference between bit-mapped and vector graphics, here are a few tips to tell which file is which!
1. Files with a TIFF, JPG, GIF, PNG, BMP or PSD suffix are raster-graphics. All photo files are raster images, which is why it is important to provide a designer or printer with the highest resolution file that you have. A low resolution 11″ x 17″ image will only be 2.5″ x 4″ at high resolution. All scanned images are also raster graphics, as are any images imbedded in a Word document.
2. Files with an EPS, AI or SVG suffix are vector graphic files. These graphics have been created by special programs such as Adobe Illustrator and various CAD programs. It’s especially advantageous for logo files, or any graphics that needs to be crisp and clear, to have been created in this format.
3. Why does a low-resolution image look fine on a computer screen or printed from a desktop printer? Computer screens are configured to show low-resolution images clearly. The same is true for most office printers. For professional printing, however, images need to be high-resolution (300dpi). So what looks OK on-screen won’t necessarily look good when printed.