Understanding basic image file types (and sizes) is a useful tool for any small business owner and could save your designer from ripping his/her hair out in frustration. Receiving a 72 dpi thumbnail image and needing to create a beautiful full page print ad from this teeny tiny spec of a photo might be Dante's ninth circle reserved for designers. The reverse can happen too. You don’t want to send a full resolution 10 MB image to your web designer either.
THE IMPORTANCE OF RESOLUTION
Let’s start with resolution. Without going into excruciating detail, images used for print media need to be high resolution, 300 dpi, or dots per inch. Images used for web and digital media should be lower resolution at 72 dpi. These lower resolution images are ideal for fast web loading.
Sizing down is easier than sizing up. You can easily resize a large, high resolution, image to a smaller 72 dpi image. The reverse is not true. As the saying goes, you can’t create something from nothing, and if the image starts at 72 dpi it is impossible to add pixel depth to get to 300 dpi. The original size is important too. Even a high resolution, 300 dpi image that starts at 3 x 5” can’t be resized to a high resolution 8 x 10” and maintain 300 dpi resolution. There will be a loss of image quality.
RASTER VERSUS VECTOR
Quick and dirty explanation of raster images and vectors. Raster, or bitmap images are made of pixels; little tiny squares of color or shades of black. Vector images are mathematical calculations from one point to another that form lines and shapes. You completely understand the difference now right? Here’s what you really need to know. Photographs are raster images and original resolution and size (see above) will dictate how much you can do with the image. Try to blow a raster image up past its original proportions and it will appear pixelated (blurred). Vectors on the other hand can be resized, small or large without the loss of resolution (without appearing blurry). Any logo file created by your designer should be provided as a vector. Vector file extensions include .AI or .EPS. If you ever plan on doing screen printing, large scale signs or banners and even some embroidery, you will need to provide a vector file.
FINALLY FILE TYPES
Vector files include Adobe Illustrator (.AI) and .EPS files. These images can be scaled to any size without appearing blurry. You probably won’t use these file types much, but your graphic designer will. You need special software to edit and sometimes view these file types.
Ah, the friendly and familiar JPEG file. These can be either high resolution or low resolution depending on how the original file is created. They are great for web use, can be used for print, dropped into Word documents, etc. It is the most highly supported file type. BUT it does not support transparency, so any graphics without a bounding box will appear with a white bounding box. See image below. For our purposes we will lump TIFF files in here with JPEG as they function similarly. If you really want to know the nitty gritty differences, a quick Google search will provide you with more than you thought existed and talk lots about compression types, but you can let your graphic designer and photographer worry about that.
PNG files are used for transparency. If you need to slap your non-rectangular shaped logo on to a different background or over top any color other than white, a PNG file with a transparent background is your friend.
PDF files are the most common file type requested by a printer. If you are running a print ad, most likely the specs will ask for a high resolution PDF. Because PDFs don't rely on the software that created them, or any particular operating system or hardware, they look the same no matter what device they're opened on.