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Some higher end cameras and all SLR (Single Lens Reflex) cameras allow you the option of shooting in RAW mode. Images stored in JPG format use 8 bits per colour channel (red, green, and blue) or 256 levels of intensity for each color. When stored in the RAW mode, the full data from the color channels is stored. In my case, 12 bits per colour channel or 4096 levels of intensity for each color. This is 16 times more intensity levels for each color. This can make a big difference in capturing fine detail in an image. Below are 3 gradient strips. The first is 256 levels of grey, the second has 1/16 the number of grey levels (16), and the final has only 4 grey levels:    There is no point in showing a grey strip with 4096 levels because your monitor wouldn’t be able to show it (some specialized monochrome monitors can, but the average computer monitor is limited to 8 bits per colour channel). So why bother with extra resolution if we can’t display it? Even if we can’t display the extra information, we can manipulate it to enhance our images. Normally, I don’t shoot in RAW mode because RAW images are very large and chew up storage space very quickly. However, I shot in RAW mode under two conditions: (1) when I want to capture as much detail as possible, or (2) there is a wide range of intensities in the image and I want to be able to fine tune how those intensities (and details) in post processing. Below is a photo I took of the National Archives of Canada in Ottawa a few years back. I took this in RAW mode, so I have the JPG image the camera saved as well as the higher colour depth RAW image. 
The original JPG image from the camera. No post processing. As you can see, it is pretty bland with not much detail. 
The JPG image processed using GIMP (an image manipulation program similar to Photoshop, but free). As you can see, it was possible to add a little more colour to the image and to bring out a bit more detail in the sky. But it is still not terribly exciting.  This is the result of processing the RAW image file. As you can see, I was able to pull out quite a lot of detail from the sky; instead of a bland, bright, grey haze, I managed to get blue sky and white clouds – details which are not at all evident in the JPG image. The downside of RAW images (aside from their size) is that most software and applications don’t recognize them. The camera makers want you to use their programs to manipulate the RAW images. Personally, I find Canon’s software to be extremely slow and sluggish. Since I don’t have Photoshop, I can’t comment on how Photoshop handles RAW images (which, I understand it does). GIMP does not support RAW images. A free RAW image editor is Ufraw, which I like much better than the Canon software.
I just downloaded the latest version of Ufraw ( version 0.17 – don’t let the low version number fool you, this is a very stable product) and and noticed that it includes lens correction filters for various camera / lens combinations. This is awesome! This makes shooting in RAW mode even more worthwhile since you can now correct for lens distortions.
[rr : this was pre-recorded since I am on holiday]
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