Mabaloo - Different Image Formats

Different Image Formats

Written by Abhishek Khatri

We come across various types of Image formats. Images on the web, your friend’s photo album, graphic images etc are common examples of images that we share and use. But, have you ever thought why certain pictures have a specific format and others have a different format. Ever wondered which format is best suited for a particular application? Using the appropriate image format is very important if good results are desired.

Widely used image formats include GIF, JPEG, TIFF and PNG. Depending on the desired quality, size and compression levels required, each format satisfies different applications. Let us discuss them one by one giving brief information about various Image Formats and their use.

JPEG - Joint Photographic Experts Group

The file extension of JPEG is .jpg and is generally pronounced as Jay Peg. This is the right format for those photo images which must be very small files, for example, for web sites or for email.

JPEG uses ‘lossy’ compression. Lossy compression implies loss in quality of an image when it is compressed and saved, and this lost quality can not be retrieved. Similarly, Lossless compression can be understood as a compression that always returns the original data, with out any difference even if compared bit-for-bit. Although, this “lossy compression” might sound to be a disadvantage when compared with other image formats but, this compression is intentionally designed to be lossy, without full recovery of the loss in quality. This allows amazing size reductions and since Web pages and email files need to be very small, they are fast through the modem. JPEG format is also used in cases where maximum image quality is not an important factor and the size is small.

The disadvantage of using JPEG is that although it helps in size reductions but, when we re-open the file and the data is accessed, it is no longer the same data which was compressed. So, if your work with images is critical and you need to be careful with the image quality, then use of JPEG is not advisable. More quality is lost every time we compress and save a JPEG file.

Since high quality along with high compression is hard to achieve, JPEG provides high compression with loss in image quality. Digital Cameras offer choices in JPEG quality. If the space in your camera’s memory card is enough you can opt for large image files but, you can at the same time compromise in quality to fit in more images in the same memory card.

PNG - Portable Network Graphics

The file extension of PNG files is “.png” and is generally pronounced as “ping”. The Portable Network Graphics (PNG) format was designed to replace the older and simpler GIF format and, to some extent, the much more complex TIFF format.

The latest of all image formats, PNG incorporates special pre-processing filters that greatly improve its “lossless compression” efficiency. The filter pre-processing causes PNG to be a little slower than other formats when reading or writing the file.

Many browsers have added features that support PNG format files on web pages to replace the GIF files for graphics. For non-web and non-graphic applications, PNG is the most used format. Majority of the programs support PNG so compatibility is never a problem.

Three main advantages of PNG over GIF, when compared for use in Web are:

Alpha channels (variable transparency)
Gamma correction (cross-platform control of image brightness)
Two-dimensional interlacing (a method of progressive display)

PNG also compresses better than GIF.

One drawback of PNG over GIF is its incapability to reproduce multiple-image support, especially animations. A PNG-like extension format called MNG corrects this drawback.

Like GIF and TIFF, PNG is a raster format, which is to say, it represents an image as a two-dimensional array of colored dots (pixels). PNG is explicitly not a vector format, i.e., one that can store shapes (lines, boxes, ellipses, etc.).

For image editing, PNG provides a useful format for the storage of intermediate stages of editing. Since PNG’s compression is fully lossless and it supports up to 48-bit truecolor-saving, restoring and re-saving an image will not degrade its quality, unlike standard JPEG.

GIF - Graphic Interchange Format

“.gif” file extensions are pronounced to sound like “Jiff” or “Giff”.

GIF uses indexed color, which is limited to a palette of only 256 colors. GIF was a great match for the old 8 bit 256 color video boards, but is inappropriate for today's 24 bit photo images. Graphics generally use solid colors instead of graduated shades, which limits their color count drastically. JPEG is much better for 24 bit photographic images on the web.

GIF is still an excellent format for graphics, and is used extensively on the web. Graphic images (like logos or dialog boxes) use few colors. A 16 color GIF is a very small file, much smaller, and clearer than any JPEG, and ideal for graphics on the web.

If GIF is used for continuous tone photo images, the limited color can be poor, and the 256 color file is quite large as compared to JPG compression, even though it is 8 bit data instead of 24 bits. Photos might typically contain 100,000 different color values, so the image quality of photos is normally rather poor when limited to 256 colors. 24 bit JPEG is a much better choice today. The GIF format may not even be offered as a save choice until you have reduced the image to 256 colors or less.

TIFF - Tag Image File Format

.TIF file extension is pronounced as Tif. TIFF is the format of choice for archiving important images. TIFF is the leading commercial and professional image standard. TIFF is the most universal and most widely supported format across all platforms. The TIFF image format is not widely supported by web browsers. TIFF is still widely accepted as a photograph file standard in the printing industry

BMP - Bitmap

The BMP file format(Windows bitmap) is used internally in the Mirosoft Windows operating system to handle graphic images. These files are typically not compressed, resulting in large file. The main advantage of BMP files is their wide acceptance, simplicity and use in Windows programs.