Your guide to common Web image formats

By | April 10, 2011
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A guide to image formats used on the Web

GIF: (Graphics Interchange Format) –This format has a maximum number of 256 colors (but it can “dither” which means mix two colors together to give the impression of another color). GIF is a “lossless” format, meaning it doesn’t get blurry or lose sharpness. It’s a great format for drawings, clip-art, icons, and such, but it’s a very poor format (because of the limitation of colors) for photographs of digital photography. GIF is the most popular image type on the Web. More GIFs are used on Web sites than any other image formats. GIFs can be made transparent and can be animated as well.

JPEG/JPG: (Joint Photographic Expert Group) — JPEG/JPG is the most common of all image formats. It’s the format your digital camera most likely uses as the default setting for saving your digital photos; it’s the most common image format on the Web. The JPEG/JPG format uses compression that reduces image file size by reducing the amount of detail contained in the image. Images with fewer details compress extremely well, while pictures with a lot of detail do not compress as well and will suffer some degradation. The amount of compression allowed (and hence the amount of details lost) can be controlled in most image editing application. Because JPEG/JPG can display millions of colors and because it has the smallest file size of all, it is the best choice for detailed images and photographs which you want to send via email or use on the Web. JPG/JPEG is the second most popular image format in use on the Web today.

BMP — The Windows Bitmap file format was the standard file format used by Microsoft Windows. Bitmap files can contain either 2 (black and white), 16, 256 or 16.7 million colors. Most Windows Bitmap files are not compressed. It is possible to save 16 and 256 color images in a compressed format. BMP files are very large and the image quality is not noticeably different from a JPG/JPEG file that is not compressed too much. Since both BMP and JPG/JPEG can display millions of colors, for most uses you’d be better off with JPG/JPEG since the file size (Kilobytes) is much smaller. You rarely see BMP format in use on the Web simply because the file size is large and would take too long to download in a browser.

PNG:( Portable Network Graphics) — PNG was invented to replace the GIF format and it is now in wide use on the Web. Coming soon to a Web site near you – Animated PNGs. Once animated PNGs are supported by browsers, PNG format may well replace GIFs on the Web. Note: For image editing, either professional or otherwise, PNG provides a useful format for the storage of intermediate stages of editing. Since PNG’s compression is fully lossless–and since it supports up to 48-bit true color or 16-bit grayscale–saving, restoring and re-saving an image will not degrade its quality, unlike standard JPEG (even at its highest quality settings). For transmission of finished true color images–especially photographic ones–JPEG/JPG is almost always a better choice. Although JPEG compression can degrade image quality, this can be somewhat mitigated – the resulting savings in image file size even at high quality levels is much better than is generally possible with a lossless format like PNG or GIF. An aside: New algorithms now exist for compressing and reducing the file size of PNGs making PNG an increasingly attractive and useful image format. We use them extensively in our newsletters and Web sites.

There are other formats too – such as TIF,TGA, ICO, and others but none of these are useful on the Web since they are not viewable in Web browsers. TIF and TGA are also very large files. The four listed above are by far the most common and the types you will encounter most often – on the Web and with your digital photos.

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