Image File Formats
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There are many different ways of encoding image data so that a computer understands what to do with it. These encoding methods are identified to the computer by an extension to the file name. For example an image called "Day at the beach" might actually be called "Day at the beach.jpg". The .jpg is the file type extension. This tells the computer that it is a file of the type JPEG and this lets the computer understand how to process the file. Besides being useful for computers to understand how to manipulate or display a photo, file extensions are important for home users to understand as well. File extensions can tell you a lot about the quality and functionality of a specific image and each file type has its own characteristic advantages and disadvantages.
Determining File TypeThe first step to being able to understand and use the different types of files that make up your image collection - and indeed your entire computers file structure - is being able to identify the different file types. File types are most commonly identified by by a three or four letter suffix appended to the file name. This suffix is separated from the file name by a period. There can be unlimited types of files because they can be defined uniquely for each program. Don't let this overwhelm you however because there are standard file types that are used universally across many different programs.WindowsThe easiest way to identify a file type in Windows is using the right click. Right click on a file and select "Properties". This will bring up a dialogue box that tells you information about the file. Included in this box is the field "Type of File". This identifies the format in which the file is encoded.To permanently reveal the file types in Windows open a folder and go to the "Tools" menu. Select "Folder Options" and then click on the "View" tab. Uncheck the box marked "Hide extensions for known file types" and click apply. This will reveal the file extensions on all files on your computer. Be careful though, if you rename a file make sure to include the file extension or else it will stop working.
OS XTo determine the file type in OS X click the file in question and type command+i to view an information box about the file. You can also set the default display of an file name by typing command+, in the Finder and selecting "Show All File Extensions" in the preferences dialogue box.BMP.bmp stands for "bitmap". Bitmapping is the process of translating an image into a grid of pixels. Bitmaps are the original method used for encoding a photo digitally. BMP is an unpatented and therefor widely used method of storing image data. Because .bmp files can be stored with anywhere from 1 to 32 bits of information per pixel images can be anything from monochrome black and white to true color output with millions of tones. BMP files also support an alpha (transparency) layer.
JPG/JPEG.jpeg or jpg are one of the most common file formats in existence. Jpeg - pronounced "JAY-peg" - is an image compression format introduced by - and named after - the Joint Photographic Experts Group. Since its introduction .jpeg has been established as a staple for image compression. JPEG is a "lossy" image compression format which means that when a jpeg image is scaled down in size some of the data is permanently lost. This is a big disadvantage when you need to display a single file at multiple sizes. If you shrink the file to the smallest size needed larger display sizes will look fuzzy. However because jpeg compression is such a highly refine algorithm higher resolution images can be stored without taking up an overwhelming amount of storage space.Many digital cameras shoot directly into jpg format. While jpegs are very useful for many applications the fact that they do not support an alpha transparency channel limits their practically for uses other than displaying and sharing photos. PNG.png files are a type of lossless bitmap image. Png stands for "portable network graphics." Png was introduced to replace the limited features of .bmp files. Png files support alpha channels (transparency), lossless compression, rasterization, gamma correction and many other powerful features.Full specifications for PNG files TIFF/TIFTagged Image File Format or .tiff is an extensible, lossless image format developed by Adobe. TIFF files can be read by a variety of different programs. Because they are optimized for extremely finely detailed black and white line art and as such they are the favored format of many scanners and digital fax devices.GIFThe .gif file extension stands for Graphics Interchange Format. GIF is a type of bitmap encoding which uses only a 256 color palette to reproduce images. Because of this GIF is not the ideal format for many applications. However GIFs do have their advantages including the ability to embed frames of animation within the file. GIFs were popularized in part by the idea that they were a way you could ensure a "web safe" image. In the early days of the Internet JPEG images - which supported millions of colors - were viewed as inappropriate for websites because they did not display correctly on every monitor. GIFs - with their limited color set - displayed well on even older monitors. Today almost all monitors support millions of colors (32 bit display) and the Internet is filled with billions of colorful images. |
