Difference between revisions of "Common Graphic File Formats for Images"
(New page: == Windows Bitmap == The three most common bitmaps, 1, 8 and 24 bit bitmaps. The number of bits in a bitmap represents the possible number of colors the given bitmap can contain. This me...) |
|||
| Line 1: | Line 1: | ||
| − | == Windows Bitmap == | + | == BMP: Windows Bitmap == |
The three most common bitmaps, 1, 8 and 24 bit bitmaps. The number of bits in a bitmap represents the possible number of colors the given bitmap can contain. This means that a 1-bit bitmap can have two possible colors, which are always black and white. The 1 bit bitmap is also known as a monochrome bitmap. | The three most common bitmaps, 1, 8 and 24 bit bitmaps. The number of bits in a bitmap represents the possible number of colors the given bitmap can contain. This means that a 1-bit bitmap can have two possible colors, which are always black and white. The 1 bit bitmap is also known as a monochrome bitmap. | ||
The 8-bit bitmap can contain up to 256 colors (2^8 = 256) and the 24-bit bitmap can have up to 16.7 millions colors (2^24 = 16.7 million). The value X-bit defines the size of each pixel in a bitmap. So an 8-bit bitmap with a width of 100 and a height of 200 takes up 100*200*8 bit = 160 KBits = 20 KB. | The 8-bit bitmap can contain up to 256 colors (2^8 = 256) and the 24-bit bitmap can have up to 16.7 millions colors (2^24 = 16.7 million). The value X-bit defines the size of each pixel in a bitmap. So an 8-bit bitmap with a width of 100 and a height of 200 takes up 100*200*8 bit = 160 KBits = 20 KB. | ||
| + | |||
| + | == GIF: CompuServe Graphics Interchange Format == | ||
| + | |||
| + | GIF streams start with a screen descriptor that defines image resolution and color depth, followed by an optional global color map (palette). GIF uses LZW (Lempel-Ziv-Welch) compression. GIF images are paletted with up to 256 colors. Each color is a 24 bit RGB value. Animated GIFs. A GIF file can contain more than one image. | ||
| + | |||
| + | Internet service provider CompuServe introduced GIF (Graphics Interchange Format) in 1987 as a format to transmit images with up to 256 different colors. In 1989 a revised specification was published that added some features to the format. | ||
| + | |||
| + | It was only later that people found out that LZW, the compression algorithm used to store the image data within GIF, was patented by Unisys. When GIF finally became popular, Unisys started charging license fees for creating software that reads or writes GIF files, even website owners who used GIF images on their site. This eventually triggered the development of PNG, the Portable Network Graphics image file format, in 1995, meant as a replacement for GIF. On June 20, 2003, the LZW patent expires in the US. In 2004 (supposedly July 7th) the patent will expire in the other countries where Unisys holds it. | ||
| | ||
[[Category:Computer Technology]] | [[Category:Computer Technology]] | ||
Revision as of 01:36, 11 February 2008
BMP: Windows Bitmap
The three most common bitmaps, 1, 8 and 24 bit bitmaps. The number of bits in a bitmap represents the possible number of colors the given bitmap can contain. This means that a 1-bit bitmap can have two possible colors, which are always black and white. The 1 bit bitmap is also known as a monochrome bitmap.
The 8-bit bitmap can contain up to 256 colors (2^8 = 256) and the 24-bit bitmap can have up to 16.7 millions colors (2^24 = 16.7 million). The value X-bit defines the size of each pixel in a bitmap. So an 8-bit bitmap with a width of 100 and a height of 200 takes up 100*200*8 bit = 160 KBits = 20 KB.
GIF: CompuServe Graphics Interchange Format
GIF streams start with a screen descriptor that defines image resolution and color depth, followed by an optional global color map (palette). GIF uses LZW (Lempel-Ziv-Welch) compression. GIF images are paletted with up to 256 colors. Each color is a 24 bit RGB value. Animated GIFs. A GIF file can contain more than one image.
Internet service provider CompuServe introduced GIF (Graphics Interchange Format) in 1987 as a format to transmit images with up to 256 different colors. In 1989 a revised specification was published that added some features to the format.
It was only later that people found out that LZW, the compression algorithm used to store the image data within GIF, was patented by Unisys. When GIF finally became popular, Unisys started charging license fees for creating software that reads or writes GIF files, even website owners who used GIF images on their site. This eventually triggered the development of PNG, the Portable Network Graphics image file format, in 1995, meant as a replacement for GIF. On June 20, 2003, the LZW patent expires in the US. In 2004 (supposedly July 7th) the patent will expire in the other countries where Unisys holds it.
