Image file format: Difference between revisions

Revision as of 04:28, 23 October 2005

Revision as of 09:17, 25 October 2005

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'''Image file sizes''', expressed in [[byte]]s, increase with the number of pixels in the image, and the color depth of the pixels. The more rows and columns, the greater the [[image resolution]] and the greater the file size. Also, each pixel making up the image increases in size as color depth is increased. An 8-bit pixel (1 byte) can store 256 colors and a 24-bit pixel (3 bytes) can store 16 million colors. The latter is known as [[true color]]. Image compression is used to decrease file sizes, and this will be discussed later.

'''High resolution cameras''' lead to large image files. Files sizes may range from hundreds of kilobytes to many megabytes depending on the cameras resolution and the format used to save the images. High resolution [[digital camera]]s record 8 megapixels (MP) images, or more, in true color. Consider an image taken by an 8 MP camera. Since each of the pixels uses 3 bytes to record true color, the uncompressed image would occupy 24,000,000 bytes of memory. That is a lot of storage space for just one image, and cameras must store many images to be practical. Faced with large file sizes, both within the camera, and later on disc, image file formats have been developed to address the storage problem. An overview of the following image file formats, '''JPEG (JPG), GIF, TIFF (TIF), PNG, BMP''' is given below.

==Image file compression==

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===JPEG ===

'''The [[JPEG]] (Joint Photographic Experts Group)''' image files are a lossy format. The standard[[DOS]] [[filename extension]] is ''JPG'', although itother may[[operating occasionallysystem]]s be seenmay asuse ''JPEG''. Nearly all digital cameras have the option to save images in JPEG format, some at different compression levels, such as “fine” and “standard.” The JPEG format supports full color and produces relatively small file sizes. Fortunately, the compression in most cases does not distract noticeably from the image. But, JPEG files do suffer generational degradation when repeatedly edited and saved. These files are best kept in original form. Because of the compression algorithm “artifacts” (blemishes) sometimes appear.

===TIFF===

'''The [[TIFF]] (Tagged Image File Format)''' image files are a lossless format., Theusing the filename extensionextensions ''TIFF'' isor ''TIF''. Some digital cameras have the option to save images in the TIFF format. These files use the [[LZW]] compression algorithm which results in lossless files. Because no image data is lost, this format is used when the ultimate in image quality is desired. Another advantage of TIFF files is that they suffer no generation degradation during file manipulation. The TIFF files support 32-bit color depth (true color). The TIFF file sizes are larger than the JPEG file sizes, because JPEG takes advantage of its lossy compression. The TIFF image format is not widely supported by web browsers, and should not be used on the Internet.

===RAW===

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===GIF===

'''The [[GIF]] file format''' is notlimited usedto foran photographic8-bit workpallete because(256 ofcolors). itsAs colora limitationsresult, it is not used for photographic work. It is still used extensively on the Internet because of the great reservoir of GIF images available, and because it supports animation. But, is being superseded by the PNG format. The GIF format does well with images having 256 colors, or less. It is not at all suitable for photographs.

===BMP===