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GRAPHICS KNOWLEDGE

ò Different File Formats! by SPYDERIX
Posted: 11 May 02 (Edited 26 Jun 03)

What file format should I use?

There are many file formats, but I will stick to the most commonly used ones.

When creating pictures for the web, you should only use either .gif or .jpg file formats.

The different files:

.BMP
ò pronounced B-M-P or bitmap
ò these files are Windows based
ò they include 1-24 bit depth
ò 4 and 8 bit images are compressed using lossless compression
ò 24 bit images are not compressed

.GIF
ò stands for Graphics Interchange Format
ò these are 1 or 8 bit files typically used for the web
ò they are small in size, and allow for fast downloads
ò they support animations, interlacing, and transparencies
ò they are best used for clip art/cartoon style graphics
ò A GIF's color palette is limited to a maximum of 256 colors.
ò Avoid using GIF's for images with complex, subtle gradations of color.
ò The GIF file format uses lossless compression to keep file sizes as small as possible.

.JPEG (.JPG)
ò stands for Joint Photographic Experts Group
ò JPEG's are 24 bit colour images and are typically used on the web
ò JPEG files are the best choice for photographs and other images with continuous-tone color gradations.
ò The JPEG format was developed to reduce the file size of photographic images while maintaining quality.
ò JPEG's use lossy compression to manage file size.
ò each time you save a JPEG, you lose some data and reduce image quality.

.TIFF (.TIF)
ò stands for Tagged Image File Format
ò TIFF's are good for the exchange of images between programs and platforms
ò 1 bit colour to 24 bit colour
ò TIFF's are generally uncompressed or they use lossless compression

.PNG
ò pronouced PING
ò stands for Portable Network Graphics
ò PNG is a very flexible format
ò These files can be palette-based, grayscale, or true color images with color resolutions of up to 48 bits.
ò PNG uses cross-platform color and gamma correction
ò indexed PNG's are almost always smaller than identical GIF files.
ò unlike GIF, which only lets you to choose a single color to be transparent, PNG provides full alpha transparency, meaning you can have images with graduated transparency
ò PNG's can carry information to compensate for brightness variations between Macintosh and PC monitors.
ò however - PNG's are not yet fully supported by the major browsers. Only Netscape 4+ and MSIE 4+ browsers support PNG's, and there are limitations. Gamma correction and alpha transparency are not consistently implemented.

.PSD
ò stands for Photoshop Shop Document
ò these files are only used to save multiple, maneuverable layers. They can be used to save Merged or Flattened Images but the file is not compressed

Compression Types
ò There are 2 different types of compression: LOSSY compression, and LOSSLESS compression

LOSSY Compression:
ò reduces file size by removing "unnecessary" data. The data is eliminated based on a number of sophisticated mathematically-based formulae. JPEG's are the only type of file that uses LOSSY compression

LOSSLESS Compression:
ò is a type of compression algorithm that reduces file size without losing any data. Typically this is done by finding and eliminating redundant information. .BMP, .GIF, .TIFF, .PNG use LOSSLESS compression


NATE


http://www.mainframe-webdesign.com

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