Image file format: Difference between revisions

Revision as of 14:07, 30 October 2005

Revision as of 19:52, 1 November 2005

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==Introduction==

'''Image file formats''' provide a standardized method of organizing and storing image data. This article deals with digital image formats used to store photographic and other image information. Image files are made up of picture elements, called [[pixel]]s. The pixels that comprise an image are in the form of a grid of columns and rows. Each of the pixels in an image store digital number representing brightness and color.

==Image file sizes==

'''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[[#Major imagegraphic file formats,|major '''JPEG,graphic GIF,file TIFF, PNG, BMP'''formats]] is given below.

==Image file compression==

'''The two categories of '''image file compression''' are: [[lossy]] and [[lossless]]. The lossy compression algorithm takes advantage of the limitations of the human visual senses and discards information that would not be sensed by the eye. The loss of information is tolerable, and in many cases goes unnoticed. Files size is reduced as file compression is increased. At some point image deterioration becomes noticeable. Lossless algorithms compress the image data with no loss in image quality, but this results in larger files than the lossy algorithms.

'''A comparison of the images''' displayed below show the greater file size of images saved in the PNG format. The photo, when viewed at its full 4 [[Pixel#Megapixel|MP]] resolution, will show differences in quality.

[[Image:CandyJaracp.jpg|left|thumb|250px|JPG file size 877 KB]]

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===MrSID===

'''The [[MrSID]] (Multiresolution Seamless Image Database) format''' is a [[wavelet compression]] format used mostly by [[Geographic Information System|Geographic Information Systems]] to store massive [[satellite imagery]] for map software.

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==See also==

* [[Graphics file format summary]]

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==External Links==