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With the explosion of scanners, digital cameras and the World Wide Web, the JPEG image format has quickly become the most widely used digital image format. It's also the most misunderstood. Here's a collection of some common misconceptions and facts about JPEG images.
Progressive JPEGs download faster than ordinary JPEGs.False. Progressive JPEGs display gradually as they download, so they will appear initially at a very low quality and slowly become clearer until the image is fully downloaded. On a slow dial-up connection, this may give the illusion of a faster download, but usually a progressive JPEG is larger in file size and requires more processing power to decode and display. Also, some software is incapable of displaying progressive JPEGs, most notably, the free Imaging program bundled with older versions of Windows.
JPEGs require more processing power to display.True. JPEGs not only need to be downloaded, but decoded as well. If you were to compare display time for a GIF and a JPEG with the same file size, the GIF would display marginally faster than the JPEG because its compression scheme does not require as much processing power to decode. This slight delay is barely noticeable, except perhaps on extremely slow systems.
JPEG is an all-purpose format suitable for just about any image.
False. JPEG is best suited for large photographic images where file size is the most important consideration, such as images that will be posted on the Web or transmitted via email and FTP. JPEG is not suitable for most small images under a few hundred pixels in dimension, and it is not suitable for screen shots, images with text, images with sharp lines and large blocks of color, and images that will be edited repeatedly.
JPEG is ideal for long-term image archival.False. JPEG should only be used for archival when disk space is the primary consideration. Because JPEG images lose quality each time they are opened, edited and saved, it should be avoided for archival situations where the images require further processing. Always keep a lossless master copy of any image you expect to edit again in the future.
JPEG images don't support transparency.True. You may think you've seen JPEGs with transparency on the Web, but in fact the image was created with the intended background incorporated into the JPEG in such a way that it appears seamless on a Web page with the same background. This works best when the background is a subtle texture where seams are indistinguishable. However, because JPEGs are subject to some color shifting, in some cases, the overlay may not appear totally seamless.
JPEG2000 is on the way and will solve all the problems with JPEG.Let's wait and see. JPEG2000 was initially proposed in 1996. More than a decade later, JPEG2000 is still not a fully published standard. It can take years before graphics software and Web browsers are able to support a new format and that can't happen until the format is finalized and accepted as a standard. Although most photo editors now support JPEG2000 (JP2) files, the major Web browsers still don't, and few (if any) digital cameras can write to this format. For more information on JPEG2000, see The JPEG2000 Source. [Update March 2014: While JPEG2000 is now a published standard, it is still not widely used or supported. In most cases, PNG or TIFF are better formats to use for avoiding the problems with JPEG.]
I can save disk space by converting my GIF images to JPEGs.False. GIF images have already been reduced to 256 colors or less. JPEG images are ideal for large photographic images with millions of colors. GIFs are ideal for images with sharp lines and large areas of a single color. Converting a typical GIF image to JPEG will result in color shifting, blurring, and loss in quality, and often the resulting file will be larger. It's generally not of any benefit to convert GIF to JPEG if the original GIF image is more than 100 Kb. PNG is a better choice.
All JPEG images are high resolution, print-quality photos.False. Print quality is determined by the pixel dimensions of the image. To print a 4 by 6 inch photo, the image must have at least 480x720 pixels for an average quality print, and 960x1440 pixels or more for a medium to high quality print. Because JPEG is often used for images to be transmitted and displayed via the Web, these images are typically reduced to screen resolution and do not contain enough pixel data to get a high-quality print. When saving JPEGs from your digital camera, you may wish to use your camera's higher quality compression setting to reduce the damage done by JPEG compression. I'm referring here to the quality setting of your camera, not resolution (which effects pixel dimensions). Not all digital cameras offer this option.
Looking for a good alternative to the JPEG format? PNG, or portable network graphic, was developed to combat the inherent flaws in both the GIF and JPEG formats. Learn more about PNG from my collection of PNG resources.
- The Pitfalls of JPEG Compression
- An Explanation of JPEG Artifacts in Graphics Files
- Which Graphics File Format Is Best To Use When?
Have a question about JPEG or another image format? Come discuss it in the forum!