There are lots of file formats for bitmapped images, and one of the most popular is JPG (pronounced JAY-PEG). It’s popular because it can provide compact file sizes. We love small files, but not when it comes at the expense of quality. The appropriate degree of image quality for your project is more important than how small the files are — especially with the size and price of today’s hard drives. Here’s how to maintain the best quality when working with JPGs:
- Before you start to make any changes to a JPG file, always save it as TIF or Photoshop PSD file before editing it. JPG uses what is called “lossy compression.” It achieves small file sizes by compressing the image and losing image information each time the file is saved. Save a JPG file repeatedly and you can wave goodbye to image quality. It will toss out more image data every time you save it — data that you can never get back. By saving your JPG file as a TIF or PSD before you work on it, you don’t lose any image quality when you save the file. Save as often as you like (which is a pretty good idea in itself) and the quality is maintained. After all the changes have been made you can convert it back to a JPG.
- Most programs that allow you to save a file in the JPG format will allow you to designate what degree of quality you want to save it at with some kind of sliding numeric scale. Even at the highest quality setting, a JPG will always be smaller than a TIF or PSD. For printed pieces, choose the highest quality available. For onscreen applications, go ahead and squeeze it down a bit. No one will ever notice onscreen.
- You can’t judge the quality of the JPG image (or any file format for that matter) by how good it looks onscreen. Your computer monitor displays at somewhere between 72 to 96 dpi (dots per inch) or thereabouts. Documents are printed at 300 dpi or more. A 72 dpi image looks great onscreen and much less than great when printed. Always choose your image resolution based on your output medium.
- JPGs taken by a digital camera will import into your image editing program at a low resolution (usually 72 dpi) but with a large image size. If an image is large (e.g., 28″ x 15″), the resolution can be increased proportionally as the image size is reduced — provided that you are resizing and not resampling the image. But if the image is small to begin with, there’s no room to increase the resolution enough to print well by shrinking the image size.
Make sense? Thoroughly confused? If you’ve got any questions about images, give us a call at 419-660-0500. We can help with anything from file conversion to image editing.