Check out this web page:
http://en.wikipedia.org/wiki/Raw_image_file
To keep it basic and simple - A RAW data file requires post processing to be made ready for printing or display.
Check out this web page for JPRG image file info:
http://en.wikipedia.org/wiki/JPEG
To keep it basic and simple - A JPEG image file is a ready to display or print file, that has been post processed to one degree or another with little or no input from the photographer.
A JPEG image file is compressed to a much smaller than RAW file size using a lossy compression algorithm, meaning some of the original image data captured when the shutter was released has been discarded. Most of the discarded data is color data.
The highest quality setting for a JPEG only retains about 25% of the original image data, a 1:4 compression ratio.
Actually, what the image sensor records is processed fairly extensively processsed even when captured as a RAW data file (de-mosaicing, color intepolation, de-noise algorithms.)
There are different types of RAW data files:
- 12-bit color depth (4096 tonal gradations per color channel)
- 14-bit color depth (16,384 tonal gradations per color channel)
Some camers offer both, meaning processing by the camera.
Some dSLR cameras only provide compressed 12-bit RAW data files. For some cameras the compressed RAW data file has also had image data discarded to make the file size smaller, a lossly compressed RAW data file.
Self-help is a great way to discover things, you didn't know, you didn't know!