Professional digital cameras generally provide two formats for writing and downloading image files: jpeg and RAW. 

Jpeg files have important advantages for photographic work. Because they are compressed, they are much smaller in size than RAW files. This facilitates sending them as attachments to emails, incorporating them in websites and printing them, actions for which the much larger RAW files might not be feasible. 

But RAW files have advantages that make them much more flexible as capture formats, that is, as the format which the camera actually writes to the memory card. Compared to jpeg, RAW files have a wider dynamic range- the range of tones which they can capture. Also, RAW files allow much broader color correction than jpeg; in fact, the color balance is not even defined in the RAW file until it is processed. This means that whatever color light in which you expose your image, the color of gray is not defined until the file is processed in a RAW editing program. 

Say that your subject is lit with flourescent light, which is quite green compared to daylight or incandescent lighting. This is very easy to correct in processing the RAW file: just select the color balance tool in the RAW processing program, click on an area that you know to be neutral gray and it’s done- your color is accurate. In comparison, adjusting color balance for jpeg files is difficult and may not even achieve satisfactory results. 

This is not to say that jpeg files don’t have their place as a capture format. A news photographer who must capture files and immediately transmit them to an agency or newspaper doesn’t have the luxury of using the RAW format. Also if  a photographer needs to expose large numbers of images in a controlled studio environment, such as for catalog work, then the quality of the jpeg file can be optimized and much time can be saved by eliminating RAW processing. 

But in situations in which images must be captured quickly without the opportunity to fine tune white balance and exposure, such as in environmental portrait and wedding photography, the RAW format can provide a path to the highest quality image production.