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But JPG is virtually always more efficient (and better looking) for photos, as seen below. But JPG file sizes and image quality can vary, so you need to understand a little about JPG compression.
JPG compression and file sizes: If uncompressed, this image would be almost 100K. When saved as a JPG with quality set to 80, the file is reduced to 10K. Raising the JPG compression to 30 (middle image) gives you a file that's only 5K, yet the loss of quality is not too obvious. The image on the right is saved with JPG compression set at 10, and while the file is only 3K, there is a clear loss of image quality. In this case, it's worth the extra 2K (1 second) of download time to use the image with 30 compression rather than 10 compression. The image on the right was saved as GIF, not only is it larger than it needs to be (at 12K), but the quality is also not as good. While you can get good quality photos from GIF files, the file sizes will be much larger than JPG files of the same images. In this case, a GIF version that looked closest to the JPG/80 image would be 29K, three to six times bigger than necessary (which means it would take three to six times longer to download than necessary).
Compression and quality will vary from image to image, so it's best to use software that gives you a preview before you save—this allows you to experiment with various levels of compression to choose the best compromise between quality and file size.
About JPG compression numbers: Different programs use different numbers for JPG compression, but generally, the higher the number, the higher the quality and the bigger the file size. You may need to look at the on-line help for your software to figure out its JPG settings.
Your original graphics files
While you must use either GIF or JPG on the Web when you're creating graphics, you should save your original work in a format such as TIF (Tagged Image File Format) or the native format of your graphics program. Why? Because both GIF and JPG compromise image quality for the sake of compression.
JPG compression and file sizes: If uncompressed, this image would be almost 100K. When saved as a JPG with quality set to 80, the file is reduced to 10K. Raising the JPG compression to 30 (middle image) gives you a file that's only 5K, yet the loss of quality is not too obvious. The image on the right is saved with JPG compression set at 10, and while the file is only 3K, there is a clear loss of image quality. In this case, it's worth the extra 2K (1 second) of download time to use the image with 30 compression rather than 10 compression. The image on the right was saved as GIF, not only is it larger than it needs to be (at 12K), but the quality is also not as good. While you can get good quality photos from GIF files, the file sizes will be much larger than JPG files of the same images. In this case, a GIF version that looked closest to the JPG/80 image would be 29K, three to six times bigger than necessary (which means it would take three to six times longer to download than necessary).
Compression and quality will vary from image to image, so it's best to use software that gives you a preview before you save—this allows you to experiment with various levels of compression to choose the best compromise between quality and file size.
About JPG compression numbers: Different programs use different numbers for JPG compression, but generally, the higher the number, the higher the quality and the bigger the file size. You may need to look at the on-line help for your software to figure out its JPG settings.
Your original graphics files
While you must use either GIF or JPG on the Web when you're creating graphics, you should save your original work in a format such as TIF (Tagged Image File Format) or the native format of your graphics program. Why? Because both GIF and JPG compromise image quality for the sake of compression.
reckoned by Monkey Goddess at 9:04 AM
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