RAW Vs JPEG

This is a subject that crops up from time to time. Here's my take on it.

In case you don't know, RAW is an image format that is 'native' to many cameras - it's the camera's own format and represents an unprocessed image. By contrast, a JPEG from a digital camera has been processed by the camera.

Let's consider the facts:

	JPEG Images are '8 bit', RAW images can be up to '16 bit'
	JPEG images are smaller in (KB) that RAW images
	JPEG images save to memory cards faster than RAW images
	JPEG Images can be used straight from the camera. RAW images require processing.

At first glance, JPEG's seem to hold many advantages - they are smaller, faster and instantly usable. However, these strengths can also be weaknesses. Let's consider them one at a time.

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JPEG Images are '8 bit', RAW images can be up to '16 bit'

This relates to the number of colors each pixel can display. Each pixel is made up of a red, blue and green channel. In an 8 bit image, each channel can display 256 different shades. Here's the lowdown:

(Most RAW formats are 12 bits, the new EOS 1D MKIII is 14 bit. For the sake of this discussion, I'll concentrate on 12 bit images.)

In practical terms, what this means is that when a 12 bit digital sensor records a scene, it can represent each pixel by choosing from 68 billion colors. Now, that's a lot of colors! If the camera is in JPEG mode, it then has to select one of about 16 million colors for each pixel - and that's a whole lot less. Now, in most scenes, this won't matter much - your eyes will see a perfectly good representation of the scene from a color palette of 16 million choices. In fact - regardless of whether you use RAW or JPEG, your eyes will probably see the 16 million color range - why? Because of your monitor's and your printer's limitations.

Where the RAW image has the advantage is when the image needs editing and there are a range of very close tones that get affected, such as a large expanse of blue sky. In an area such as a blue sky, the JPEG really only has 256 shades of blue to manipulate - the red and green channels will play far less of a role here. The RAW image has 4096 shades of blue at it's disposal, and this is a definite advantage as it will give smoother transitions between the tones.

JPEG images are smaller in (KB) that RAW images

This is undoubtedly true - a JPEG is often 4 or more times smaller than the equivalent RAW image. What accounts for this? JPEG uses a special form of compression known as 'lossy compression'. Lossy means exactly what it says - it literally throws pixels away to achieve a smaller file size! And once they are gone, they are gone for good. Now, for a small print or onscreen viewing, the difference between a 'fine' quality JPEG and a RAW image is imperceptible. However, a large print, especially one that is resampled may well show up the loss of quality that discarding pixels incurs.

Additionally, each time a JPEG is saved the image is re-compressed and more pixels may be thrown away, depending on the editing that is done to it. As a general rule of thumb, a JPEG can be edited and saved once and retain sufficient quality for a small print or a web image. More edit/save cycles than that and the loss of quality will become apparent.

There is one definite advantage that JPEG's have - more of them fit onto a memory card. However, with memory cards becoming larger and cheaper this advantage is no longer a decisive one.

JPEG images save to memory cards faster than RAW images

The performance of a top level digital SLR is phenomenal - the new Canon 1D MKIII can shoot 30 RAW images at 10 frames per second! However, it can shoot 110 JPEG's at 10 frames per second. And this is reflected across the board with more affordable prosumer and consumer cameras. Being smaller, JPEG images do write to the memory card faster, which can be the difference between the camera being ready to take an image or not being ready.

When I used a 300D, Canon's first affordable digital SLR, the wait for the camera being ready to take the next RAW image seemed like an age - switching to JPEG made the camera feel a lot faster. Whilst on vacation in Portugal I visited the Aquamarine Centre at Guia and photographed a very fast dolphin show - I had to switch to JPEG mode to give the camera a chance to keep up.

Since moving to the 30D, I have never encountered a situation where its RAW mode wasn't fast enough for me.

JPEG Images can be used straight from the camera. RAW images require processing.

Cameras offer all sorts of settings so that a JPEG can be produced with the contrast and saturation nicely boosted or reduced and the image sharp and ready for printing. So why bother with RAW?

JPEG's are fine until the camera settings are wrong for the scene - then the image needs editing anyway and RAW images can have their white balance, saturation, contrast and a host of other parameters adjusted with absolutely no loss of quality. Changing these parameters in a JPEG will have a small effect on its quality.

Conclusion

I've tried to give a balance assessment of the strengths and weaknesses of the RAW and JPEG format. Personally, if you have the time and the equipment to use RAW I feel you'll get the best possible results from your camera. That's not to say JPEG doesn't have it's place.

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