One of my colleagues is in the process of buying a Digital Rebel XT. This is my current favorite camera. I am sure that my colleague will ask about what format of picture to take. Well Steve, this is for you.
There are couple of different formats that you can take with the Digital Rebel XT and equivalent Digital SLR cameras. Their are typically two different formats that you can take, JPEG or RAW. Pretty much all cameras take JPEG and RAW is something quite different. Read on for more information.
JPEG — This is the standard format used by most digital cameras. JPEG is a lossy format meaning that when the picture is taken and the camera creates the JPEG some of the image data will irreparably lost. This may not seem like a big deal but if you then edit the JPEG and then re-save it, you lose more detail. Thus every time you edit a JPEG and re-save the image as a JPEG the quality will degrade.
There is a an upside to JPEG which is that it is the most commonly used and understood format and can be viewed in any standard web browser. The other element is that the resulting file sizes are smaller than alternatives because of the lossy nature of the algorithm.
Pros: Well understood and easily viewable, small file size
Cons: Reduced image quality, image degradation when editing
RAW — This format is a lower level format. When you a take a picture, the sensor in the camera captures the image on its sensor and the sensor outputs the image information. In a JPEG environment, that output is then processed in camera and turned into a JPEG. The RAW file contains all of the raw from the sensor with no processing. Thus it contains all of the possible image data from the sensor and is the highest resolution image possible from the sensor.
Also because the image has not been processed inside the camera, you can fix common image problems much more easily. An example of this is improper white balance which often occurs with digital cameras. The result is that the colors in a picture are skewed and you may see a bluish tint. This is easily fixed with RAW images and is more difficult to treat with JPEG.
The downside of RAW is that it is a proprietary format for each camera manufacturer. Thus if you shoot a RAW photo and send the RAW picture to someone, it is unlikely that person will be able to view the file. This means that some element of post-processing will be required with all RAW images to convert them to a more common image format such as JPEG.
Pros: Highest resolution image, improved image editing ability
Cons: Proprietary format, larger file size than JPEG
For the average photographer JPEG is adequate. However, if you are looking for the best image quality you should look at RAW. The Digital Rebel XT also has the ability to simultaneously take RAW and JPEG. This potentially overcomes the weeks of RAW, but results in more than 2x the required storage space for each picture which is problematic IMO.
I generally find shooting RAW to be the preferred method. I always take RAW and then perform a batch conversion of all RAW photos to JPEGs using Photoshop. This way I always have RAW and JPEG version of all pictures. I prefer to perform the conversion on my computer to minimize the amount of space required on my CF Card.