Learn how to resave a JPEG

by Guest Contributor | Sep 29, 2003 7:38:00 PM

Tags: Guest Contributor

Takeaway: Once you export a JPEG, you're working with a compressed imitation of the original. Find out the best way to resave a JPEG.

By Paul Anderson

You should export an image as a JPEG only once, because once you export, you're working with a compressed imitation of the original. The proper procedure for editing a JPEG is to modify the original image and then re-export it as a JPEG.

But sometimes you don't have a choice: you may have lost the original file or never had it to begin with. For example, some clip art vendors use the JPEG format to pack more images onto a disc. When you're stuck, there are some tricks you can use to ease the pain. With moderately to highly compressed JPEGs, or with images that have already been resaved, the main problem is eliminating the subtle defects, or artifacts, created by JPEG encoding.

One trick is simply to shrink the image a little. Assuming your editor has antialiasing, many of the artifacts will get interpolated away.

If you don't want to scale down the image, you can get help from filters. Most good image editors list them as Filters or Effects in the menus. A Blur or Unsharpen filter can be helpful here, especially if it has adjustable settings. Mildly blurring the whole image can make the artifacts less noticeable when the JPEG is re-encoded. Other filters that may work include Despeckle, Reduce Noise, and Remove Dust And Scratches. By weeding out tiny imperfections, which the computer can see much better than you can, these filters can eliminate JPEG artifacts directly. Experiment to find which one works for your image--but keep the Undo command handy!

When you're done altering the image and you're ready to resave the JPEG, be sure to also save the image in a true format so that you don't ever have to re-encode it again.

Paul Anderson is associate technical editor for CNET Builder.com. His responsibilities don't include handling graphics, so naturally, he handles them all the time.