A few weeks back I wrote a post about RAW and JPEG. In it, I told a little story about baking a cake and I let on the fact that I was a complete chocoholic. Well, for those that found that post interesting, this may tick a few boxes too.

A couple of days ago, one of the blog readers, Steve, dropped me an email with two small histograms attached. They were from the same image but one was the RAW version of the file and the other was the JPEG. Now at first thought, you may expect the histograms to look the same. But they don't. Similar yes, but the differences are obvious - and they show the advantage of a RAW file over a JPEG. 

 On the left is the histogram from the JPEG file, on the right is the histogram from the RAW file. Can you spot the difference? 

Well, it's quite obvious if you look at the edge of the trace lines - the RAW file histogram has a smoother outline with fewer sharp peaks and troughs. The question is... why? 

Well, it's quite simple really, and it's to do with bit depth. Bit depth defines how many different, or unique, colours an image can contain. A JPEG file can only be 8bit wherease a RAW file from the camera used to produce this image (an EOS-1D Mark III) is 14bit. While 8bit provides 16.7million unique colours, 14bit provides 4.3trillion unique colours.

It's this extra colour data and the corresponding smoother tonal gradation between each tone that makes the histogram smoother. 

Does this mean that RAW is better? Well, if you're planning on trying to really maximise the ability of your camera to capture data so you can have the most data to work with afterwards, then yes, RAW is better. However, you need to ask the question of whether you will notice the difference in the final image. In many cases, it's unlikely you would, but you can never tell beforehand what the final use of an image will be so my view is to capture as much as possible and throw data away rather than capture less and be unable to create it. 

As an addition to this, people often ask about printing and the fact that surely you need an 8bit file. Well, that used to be the case, but modern printers are so good now, especially the Canon PIXMA range, that they can deal with, and make use of, a 16bit file. This means prints look better, colours are more accurate and there is less chance of tonal stepping where gaps emerge between discrete colours because of extreme image processing.