Monday, January 29, 2007
May 2005 HelpLine
Why Not JPEG For Everything?
Q) The February 2005 issue featured an article on using the JPEG file format, "The Power Of JPEG." My confusion is that after reading all the good info regarding JPEGs, it's recommended that after opening a JPEG file, never resave it as a JPEG, but convert the image to TIFF. If JPEG is so good, why convert? I have hundreds of photos in JPEG folders and have never had a problem. TIFFs take up a lot of space; I'd need a new hard drive just to save converted JPEGs.
Frank P. Kennedy
North Branch, Minnesota
A) The short answer is that while JPEG is a great file format, it's a compressed format. When you view (or open) a JPEG in an image editor, you're converting a compressed file to an uncompressed display file. If, after making adjustments, you resave the file into a JPEG file format, you're recompressing the file. Every time you compress, you're throwing away data and adding artifacts-this can affect the quality of your image, especially in fine details and color gradations. Therefore, after making adjustments save your file as an uncompressed TIFF file.
If you're only viewing the photo, you can keep the files in the JPEG format—just be sure you don't resave the image. Closing it doesn't change the file and isn't saving it. Since the image already is on your hard drive, it's saved—resaving means saving changes or telling the program to save it rather than just close it. This is an important distinction, closing vs. saving.
Here's my workflow: After shooting, I download my files from the memory cards to my computer. After deleting any images that I don't want and batch-renaming them to something more meaningful than DSC10001.jpg, I immediately archive them in their native format (some are JPEG, some are RAW) to an optical disc (CD or DVD, depending on the number of images). Then I begin any adjustments to the files that are on my computer, resaving the edited images in the native format of the image-editing application that I'm using. When I'm satisfied with my adjustments, I also save a copy of the file in TIFF format.
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