For my third blog installment on graphic formats, I will go over raster graphics.
Have you ever noticed when you zoom into an image or try to make one bigger that it gets grainy or pixelated or when you print some images they print blurrier than they appear on your screen? That is because these images are raster graphics and are a set size based on the number of pixels it contains and how dense those pixels are on a grid.
Typically, the size is measured in dots per inch (DPI) or pixels per inch (PPI), which are essentially the same thing. As I discussed in Part I of this series, 72 DPI is typically referred to as a low-resolution image and is more commonly used in digital/web formats. 72 DPI images do not work well in print formats. Instead 300 DPI resolution is best for print and is considered high resolution.
Therefore, pulling images off the internet or using your snipping tool is not sufficient for quality, professional-looking print artwork (not to mention you likely are using an image to which you have zero rights, but that is a whole other blog topic). There is also no magic tool for adding pixels or converting a small, low-resolution image to a larger, higher-resolution image.
Common raster graphic file formats and uses are as follows:
JPEG (or JPG) - Joint Photographic Experts Group
JPEGs are very common, and probably the graphic file type with which most people are familiar. These images are a rectangular shape and have a non-transparent background, usually white for images that do not fill the entire rectangular space, such as a logo. JPEGs can be used for digital/web formats at a low-resolution as well as in print formats at a high-resolution.
PNG – Portable Network Graphics
PNGs are best in web formats and have the capability of a transparent background. They are typically low-resolution, so it is not best for printed materials.
GIF – Graphics Interchange Format
GIFs are another graphic format best in web formats. GIFs can also support animation. The colors are limited with GIFs, which allows for the image to load very quickly in web format; however the image quality is much lower.
PSD – Photoshop Document
PSDs are created in Adobe Photoshop. Typically this file type is used to modify, manipulate or create images. PSDs are used to create the raster graphic formats above and can create both high- and low-resolution images.