First, a little background as to what I'm talking about (although if you are reading this, you probably already know what I'm talking about.) The Canon 10D, as do all digital SLRs, stores photos in one of two formats -- either RAW or JPG. RAW files are the raw, unprocessed data directly from the camera's sensor. They have had no sharpening, saturation, contrast, or white balance adjustments applied. For this reason, RAW files have been likened to a "digital negative." That is, you can keep going back to the RAW file and "develop" it again and again using different settings in your conversion software. A JPG file on the other hand has been processed by the camera. Whatever settings you had in effect when the picture was taken have been applied to the image that is stored on the memory card. So if you look at the photo on your computer and you see that it's oversharpened because you accidentally had the sharpening set to +2 instead of 0, you are out of luck. What's done is done and can't be undone. The same goes for saturation, white balance, etc.
Now for the advantages/disadvantages of each. First RAW:
Now on to JPG:
Now, this is probably a simplified list for each, but these are the things that I personally see as the good and bad for both formats. I want to touch on the file compatibility issue again for just a second. This is something that gets discussed a bit but I don't think it gets the attention it deserves. As I said, RAW files are proprietary. Each camera maker's RAW format is different and therefore you have to have the software from that manufacturer in order to convert the files to something useful. Yes there are third party applications for every camera but they all still use the manufacturers conversion library to do their jobs. This makes me nervous for a couple of reasons. I take a LOT of pictures and in 10, 20, 30 years I want my children to be able to pull out my CDs/DVDs and look back at pictures from their childhoods. Well, in order to do so they will have to have the RAW conversion software on their computers to look at them, and what are the chances of that? If I shoot JPG, they pop in the CD and start the show. What if in 20 years I want to go back and make prints from my pictures, will I have the conversion software? What if I do but it's not compatible with Windows 2025? Many people shrug these arguments off as being non-issues. "Oh just put a copy of the conversion software on every CD you burn and you'll be fine" they say. Well maybe, maybe not. I'm not willing to take that kind of chance with my memories. I take way too many pictures to risk not having them viewable in 20 years. So convert them all to JPG and burn those too you say? Well that gets into a lot more time and effort on top of the time and effort that RAW already costs me. What if we go on a family vacation and a family member wants a copy of the CD with the pictures on it? With JPG, just make them a copy. With RAW, you have to convert the whole lot. More hassle.
A second scenario which is worth mentioning is this. Let's say you are on vacation and you want to stop off at the local photo lab and get prints of what's on your memory card. With JPG, no problem. With RAW, no go. Their equipment will not read your RAW files and you can't get prints. I know that this is probably a rare occasion, but you never know when you might need to do just that.