Some common image formats

Common formats

GIF 

This is an 8 bit format, so maximum number of colours supported by it is 256.
Uses the LZW compression algorithm.
Developed in 1987 by CompuServe to provide a colour image format for their file downloading areas.
Enhanced in 1989 to support for animation delays and transparent background colours.

The format favours flat areas of uniform colour with well defined edges - so it is well suited for logos and other sharp-edged line art with a limited number of colours and simple animations.

PNG

pronounced Ping
A bitmap graphic format which uses lossless compression.
Developed to surpass the limitations of GIF format.
Patent-free,
It has better compression than GIF, although the difference in compression rate for small images is no more than 5%
It allows up to 24 bit in colour, so supports millions of colours and provides greater depth of colour,
Doesn't support animation.

BMP

An uncompressed proprietary bitmap format which was invented by Microsoft:  today, there is no reason to use it.

TIFF 

Tagged Image File Format:   a format released in 1992 by Aldus (Adobe Systems)

In principle, it is a very flexible image format that can be lossless or lossy, because the details of the image storage algorithm are stored in the file.

In practice, most graphics programs which use TIFF do not do any compression, so it is used almost always as a lossless uncompressed image storage format.   Because of this, TIFF file sizes are quite big.

Some programs use LZW )a lossless compression algorithm) with TIFF files, but it's not universally supported.

PSD, PSP, 

These are proprietary formats used by graphics programs.

• Photoshop files are .PSD, 
• Paint Shop Pro files are .PSP. 

These are the preferred working formats as you edit images using these tools, because only the proprietary format for the program gives you access to all the editing features.

For example, these packages use layers to build complex images, and layer information is lost in non-proprietary formats like TIFF and JPG.

That said, it is good practise to always save the end result as a standard TIFF or JPG file (as well as the PSD or PSP) to maintain forward compatibility if the applications have major changes in future.

Some other proprietary formats:

• AI – Adobe Illustrator File
• CDR – Corel Draw File

Proprietary simply means that the file format is not open source, ie it is the property of the company who invented it or whoever they have since sold the right to.

Compression algorithms

Compression algorithms are ways of saving data in a computer file, so that the amount of disc-space used by the data is less than the standard format.

Lossless and lossy are words terms that describe whether all original data can be recovered when a compressed file is uncompressed.
Lossless:  every single bit of data that was originally in the file remains after the file is uncompressed.
Lossy:   some data is missing.