Digital photos are stored as files on memory cards and computer hard disks. They can be stored in different file formats (each format has a unique file extension). Most of the formats are compressed to save space and each has its own pros and cons. Lossless compression is usually applied to text and other data where all data is equally important. For example when compressing the text in this article and later on decompressing it you would want to get the exact original article without any words or sentences dropped by the compression software that decided they were not important. Lossy compression is usually applied to digital photos and graphic files. Such files include data that the viewer would not be able to notice if removed. For example small changes to color in a photo might not be noticeable. The decompressed file is not exactly the same as the original one but when viewing both the original and decompressed photos side by side the viewer can not tell the difference. Lossy compression software can be set to different compression levels based on how much data is allowed to be lost. At some point losing too much data is noticeable and degrades the digital photo quality. Many digital cameras allow you to set the level of compression from low to high where high compression means smaller files but less quality and low compression means bigger files but no noticeable quality degradation. Common digital photo file formats You can know what a digital photo file format is by checking its extension. Usually the extension is three letters representing a specific format. Here is a list of the common extensions and formats: BMP Windows Bitmap: this is a basic raw format. The photo is stored as a pixel raster and is not compressed. While this format is very easy to use and is supported by practically all software it is not efficient as there is no compression applied. GIF Graphics Interchange Format: An old file format initiated by CompuServe. It uses a lossless LZW compression and is thus more efficient than BMP files. GIF files are very efficient for storing basic graphics (that include lines, circles and other graphical shapes) and also efficient for storing small digital photos but are rarely used to store large digital photos as there are more efficient formats for that purpose. GIF files can also include multiple "frames" and support basic animation. PNG Portable Network Graphics: This relatively new format was designed to be used in online applications such as web pages. It uses a lossless compression. The original goal of the PNG format was to replace GIF (due to some licensing complications associated with the GIF format). PNG is commonly used now by online web sites to represent small digital photos or graphics replacing the GIF format. JPEG Joint Photographic Experts Group: Also known as JPG this file format was designed by a special industry group and became an ISO standard. The design goal of the format was the efficient storage of digital photographic files. Although JPG files can support lossless compression they are almost always used in lossy compression mode. JPG files are very efficient in compressing digital photos. The JPG compression software can be set to different compression levels with higher compression levels the photo files can get very small but they can also get distorted. JPG files are the most common ones used by digital cameras to store compressed digital photos on memory cards and computer hard disks as they result in small file sizes and hardly any noticeable photo quality degradation. |
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