Image file format

Under Construction

Compression:
There are two basic types of compression.
Lossless - You can get the exact image back when opening it again. e.g. png or gif
Lossy - Data is discarded. e.g. jpeg
Lossy formats are more compressed but each time you edit them they get worse.
It is better to save a master copy in a lossless format and then save them as jpeg's when uploading to the internet or sending via email.

File
extn type comrees-
sed loss

.gif GIF - Graphics Interchange Format - Compuserve y lossless¹

.png Portable Network Graphics y lossless

.jpg JPEG-JFIF - Joint Photographic Experts Group y³ lossy

.tiff TIFF - Tag Image File Format n² lossless

.psd Adobe Photoshop n lossless

.pct PICT - Macintosh picture format n lossless

.cr2 Canon Camera Raw n lossless

.raw Raw format from Photoshop n lossless

1. Gif is limited to 256 colors, so if an image contains less than 256 colors it produces lossless comression, otherwise colors will be lost.

2. Sometimes a lossless compression algorithm called LZW is used with tiff images, but it is not universally supported.

3. Most graphic programs allow you to save jpeg images with different quality levels. Higher quality results in larger file sizes. Photoshop has levels 1-12, others use 1-100.

Output form Cannon EOS Rebel
10 MP camera 3888x2592 pixels

format	size MB
.CR2 (camera raw)	12.9
.jpg (camera)	3.2
.jpg (PS 12[max])	5.9
.jpg (PS 6[med.]	1.0
.raw (PS elements)	30.2
.psd (Photoshop)	27.9
.tif (Photoshop)	30.3
.pct (Photoshop)	27.9

See Image Filetypes.

PS - PhotoShop - Number refers to quality level.

Information such as small icons and thumbnail images are stored with the image increasing the file size significantly. You need to set preferences in your graphic program to save without these. They are usually deleted when you ftp to a web site.

cropped picture 322x207