Maybe I should probably post this in a photography forum, but it seems like a simple question so possibly not worth the effort...
Anyway, the question is, what is the point/advantage of shooting in RAW format?
My understanding is that RAW is is effectively the raw, unprocessed output of the camera sensor. Besides giving control over noise reduction and compression, what advantage does shooting in RAW give you? Surely you can adjust the saturation, contrast etc. for a JPEG just as easily?
JPEG compression deletes a certain amount of the information captured by the sensor. You can recover more information about each pixel with a RAW file, this allows you to do more with the picture to recover exposure etc.
In essence, you can't alter information that the JPEG has forgotten.
jpeg compresses things the eye doesn't see well, to reduce file size. On a given picture, if you are printing it out as it is shot, this is probably fine (assuming not too much compression is used)
however, if you want to play with the image after it is taken, this compression may become obvious. For instance, if I wanted to brighten an image up, I can do so on a raw\jpeg just as easily, but the dark areas of the image will have been heavily compressed in the jpeg (as they can't, when dark, be seen). When lightened, the picture then looks crappy.
I don't do anything to my photos after snapping them, apart from very occasionally tweaking levels a tiny amount, so I'm happy losing some of the flexibility of doing that, to gain some of the advantages (size, compatibility, ease) of using jpeg.
JPEG stops uses an algorithm to reduce the amount of data on the image. This means that the RGB or HSI values of individual pixels are not what was actually captured, but an approximation. You can adjust all those things you mention, only the effect it has on the pic will not be so well defined
Surely you can adjust the saturation, contrast etc. for a JPEG just as easily?
No, you can't. You can in Raw, you can't in JPG.
So when I use the brightness, contrast etc. controls in Photoshop what is it doing in that instance then? 
to simplify, it's like stretching a rubber band. the more you stretch it, the thinner it gets and eventually it breaks. having a RAW image is like starting with a bigger rubber band in the first place, you can stretch it more before it gives up
As everyone has said there's lots of information in the raw that gets lost creating a jpg.
That lets you do stuff you couldn't with a jpg.
For example if you mess up and overexpose you can adjust the raw by 2-3 stops (each stop removes half the 'light'). Which is a lot.
If it's dark and there's high iso noise you can remove it. Something you would have had to consider before taking the shot with a jpeg.
You can sharpen a raw better than you can a jpg.
In fact you caqn make all kinds of decisions after the event that you would have had to make before hand with jpg.
So when I use the brightness, contrast etc. controls in Photoshop what is it doing in that instance then?
Theres much more to it than just compression and non-compression.
The RAW 'image' is litterally just the sensor data from the camera. You'll need the appropriate plug in for your photo-editing app to load it or use the software that comes with your camera.
Because its the sensor data and not an image, you can edit it to the nTh degree and not loose and information. If you edit in JPG, the image will deteriorate as it is edited as data is overwritten with your edits. With RAW, this doesn't happen. You can always go back to the original image. So even if you were to save the RAW image with the edits, close the app and go back in, you can still revert those edits if you wanted. So, editing in RAW is a safe way of editing images.
Also, you can post-process the image as if it was still on the camera or even as if the image is about to be shot again. For example, if you find that the image is under exposed you can apply exposure bias to correct it, or change the colour correction, white balance or even the exposure duration. So if you have your RAW image you can rest assured that even if the image looks bad on the LCD screen, at post-processing you can correct it.
Tip: It's always better to under expose than to over expose. 
Ok, but to say that you categorically cannot alter the stauration, contrast of a JPEG is a bit misleading, surely?
EDIT: Lots of replies in the meantime.
Ok, but to say that you categorically cannot alter the stauration, contrast of a JPEG is a bit misleading, surely?
For example, when adjusting brightness the blacks are black. The whites are white. You can't really adjust them.
In raw there is information on how white and how black things are.
You can do that, but it's not as accurate. During the compression of the image, the sensor data is essentially lost. Also as you edit, you will see a sapia effect as you expose the lost areas, which looks very ugly.
Ok I think i'm getting there. A quick googling suggests that one of the main differences is the application of a logarithmic function to the sensor data, which would account for the irreversible reduction in colour/brightness depth. Thanks all....
poppa - Member
Ok, but to say that you categorically cannot alter the stauration, contrast of a JPEG is a bit misleading, surely?
It's not misleading, it's incorrect. I only shoot jpegs and alter them quite a bit. Whether it's the 'cleanest' way of doing this, is a different matter.
With regards to jpegs losing quality every time you make a change and save - is that really an issue? Just make the changes and do a save as, keeping the original file intact. The degradation over 1 save will be unnoticeable.
RAW is 'better', but for 99% of applications, 99% of the time, jpeg will be fine.
The advantages of using RAW (as I see it) are pretty much outlined by 5thElefant, above. Plus, you can also alter the white balance very easily.
I shoot in RAW+JPG Basic. The reason for this is if I do take a good shot but for some reason theres a problem, it can be recovered easily with RAW without and deterioration to the image. It's mostly for flexibility after the shot has been taken and not really because one is better than the other.
To be fair, you have to have the right software and know what you are doing to get any real gains using RAW over JPEG.
Put in simple terms...
A RAW image will capture all colours, shades, tints, tones etc in the range 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
The largest file .jpg may only actually capture 0, 2, 4, 6, 8, 10
A heavily compressed .jpg may only record 0, 5, 10
And as .jpg is NOT a lossless format, when it is gone, it is gone so no amount of altering saturation, contrast etc will bring back 2, 3, 4, 6, 7, 8 and 9 to a heavily compressed .jpg - just approximations of what the manipulation programme thinks may be right.
A good example might be with a sky.
Say for example, you expose for someone's face, but then the sky is overexposed and pure white when you look at your image on the camera preview.
In JPG there is no detail there. Just a big area of white. No amount of adjustments can bring back detail there.
In RAW, you can lower the exposure of just that area of sky, bringing back slight cloud detail - enough to make it not clipped/blown.
It's like magic!
The camera recorded a wider range of detail than any one JPG can show. Raw lets you show different amounts of exposure/saturation/etc information in different areas of the image.
Another common example of this is a subtle HDR image where you bring back detail in the shadows AND in the highlights. It gives a different look to the image, but many people like it.
Because its the sensor data and not an image, you can edit it to the nTh degree and not loose and information. If you edit in JPG, the image will deteriorate as it is edited as data is overwritten with your edits. With RAW, this doesn't happen. You can always go back to the original image. So even if you were to save the RAW image with the edits, close the app and go back in, you can still revert those edits if you wanted. So, editing in RAW is a safe way of editing images.
Whilst the rest of the stuff about the advantages of RAW in various posts above is true, this bit is not really true. For example if you edit in raw, and apply an effect to the image, it is not always possible to undo that effect, you should still save as a separate image.
I think there are some raw editing programs that essentially don't process the image at all until you save it out to a non-raw format, which I guess might be where you're getting confused?
Put in simple terms, RAW give you more ability to manipulate the image into what a decent photographer would shoot in the first place.
druidh - skill compensators are always welcome
A RAW image will capture all colours, shades, tints, tones etc in the range 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10The largest file .jpg may only actually capture 0, 2, 4, 6, 8, 10
A heavily compressed .jpg may only record 0, 5, 10
You're kind of putting dynamic range, and compression together, which are both differences between raw and jpg.
The big advantage of RAW is dynamic range, taking your example above, a RAW image will capture
0,1,2,3,4,5,6,7,8,9,10
whereas jpg will capture 3,4,5,6,7
So if your image is too dark, with raw, you can change it so you see 0,1,2,3,4,5 and have a lighter image which still has detail in the dark areas.
Compression is a whole different thing, but if you select the best quality jpg compression on a good digital camera it makes next to no difference unless you look at individual pixels.
Joe
I think there are some raw editing programs that essentially don't process the image at all until you save it out to a non-raw format, which I guess might be where you're getting confused?
I don't know ANY programs that alter the RAW file itself (apart from some that change the metadata). You ALWAYS have to save the file out to a non-RAW format.
< awaits being shown to talk rubbish >
^^^ If that is the Joe Marshall who died last year, you should listen to him!
From what I read it's not just about JPEG compression either, it's about converting the raw sensor data to an image format. You could convert the raw data to a bitmap with zero compression, but you would still lose an awful lot of information.
The big advantage of RAW is dynamic range, taking your example above, a RAW image will capture
0,1,2,3,4,5,6,7,8,9,10whereas jpg will capture 3,4,5,6,7
Oooohhhh ....
Now you're mixing up dynamic range and bit depth ...
A jpeg can still represent white and black.
http://theonlinephotographer.typepad.com/the_online_photographer/2009/02/dynamic-range.html
A jpeg can still represent white and black.
But a raw can represent 'whiter than white' and 'blacker than black', ie. it can represent something that is whiter than the level that is white on the jpg. You can have an RGB image where the level is 255,255,255, and the raw allows you to darken it and get a whole load of detail out.
There is a higher bit depth which in part allows for the higher dynamic range, but also allows for slightly more colour detail, but realistically how many people can really see that detail, and I'm not sure how much difference it realistically makes to any processing.
Or at least that's how I see it, but I could well be wrong!
Joe
I WAS trying to put it in simple terms though - I accept that to someone with greater knowledge it wasn't entirely 'correct' as such. I was just trying to get the OP to see it in simple terms.
Shall I go simpler?
For a jpg, look at each pixel as a light switch - it either has the information ('ON') or it doesn't ('OFF').
A RAW image is more like a dimmer switch - 'ON' and you can see everything, 'OFF' and you can see nothing, but at any point in between there are different levels of detail to be seen/hidden.
Possibly.
I don't know ANY programs that alter the RAW file itself (apart from some that change the metadata). You ALWAYS have to save the file out to a non-RAW format.< awaits being shown to talk rubbish >
Ah right, I only really use raw either in HDR programs, where I essentially convert it to an HDR image format then piss around with it there, where saving certainly does mess around with the file itself, or in the processing software that came with my camera, where you basically can only apply effects and convert to jpg, so there is no intermediate file.
poppa - loads of sensible type stuff up there but can't see anyone has mentioned what, to me, is the simplest explanation - take the same shot in RAW and JPEG (if your camera has High / Med / Low setting for JPEG be sure to use high - or all 3 to give a full comparison...)
Copy the shots to your computer - just a straight copy.
Now, open the folder you dropped the shots in and compare the file sizes - you'll see even from RAW to High quality JPEG a large chunk of data has 'gone missing'.... never to be seen again.
As said above, if you don't have the date there you cannot use it. Not always an issue but, if you're getting into heavy image manipulation / huuuuge enlargements then the more data you have to play with, the better...
I don't know ANY programs that alter the RAW file itself
RAW is ostensibly read-only; if you did amend one, you'd get a second file with all the change data in it (.XM- something, .XMP? Maybe.)
RAW is basically what your camera sees. JPG is that information with your white balance, sharpness etc ("Styles" in Canon parlance) applied to it.
JPG vs RAW is "processing in camera" vs "processing on a PC." All other arguments aside, it should be fairly apparent that shooting JPG will be simpler / quicker but shooting RAW will give you the most time to make decisions about levels (and change them) in post-processing.
Sure, you can change JPGs in Photoshop; but if it were traditional media which would give you the best results, time in a darkroom with the negatives and jars of chemicals, or a folder of 7x5" prints and a box of felt tips?
I don't know ANY programs that alter the RAW file itselfRAW is ostensibly read-only; if you did amend one, you'd get a second file with all the change data in it (.XM- something, .XMP? Maybe.)
Well, just for the sake of pointless pedantry, iView can overwrite the metadata header in a RAW file and I guess Capture NX can do likewise, but altering the pixel data itself would be amazingly stupid.
... which if you read up, is what DrJ said in the first place. It got lost in the re-quotes.
Another thing - your camera applies noise reduction and sharpening etc to the image before making a JPEG. If you shoot RAW and do this yourself, you can experiment with different options and settings to get what looks good for that particular image. If you don't like it you can go back and tweak it differently. You can also (I think) chop up the image and apply different settings to different bits of it...
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