RAW or jpeg?
Here's my conclusion, you can read the reasoning down the page
For underwater photographers the colour control benefits of RAW are likely to be the most useful and will be immediately obvious. At normal print sizes, or when viewed on-screen, the image quality benefits of RAW aren't likely to be visible. Shooting RAW, if you have it, has no real drawbacks except the additional time and effort required to view your pictures, but shooting jpeg doesn't mean your pictures will be less 'good'.
Shot in jpeg, using an external flash on a compact camera. Using an SLR and proper macro lens, and shooting in RAW would have delivered technically better image quality, but the picture wouldn't have been any better!
jpeg
jpeg is the most common electronic format in which images are stored and viewed . A jpeg image is made up of discrete dots, each of which has a brightness level for red, green and blue colour values. When viewed from far enough away the dots aren't visible, just the colours and tones of the image. To record a jpeg file the data captured by the camera sensor is processed, which can include interpolation of image size, sharpening, colour saturation and contrast adjustments.
This lionfish image was resampled to 50 x 36 pixels, then blown up to clearly show the individual dots that make up the image and the transitions between dots of almost-but-not-quite the same colour and brightness
When viewed at a more appropriate size for the number of pixels it looks more like a lionfish!
jpeg images can be recorded at different quality levels. When a jpeg image is recorded image-processing software looks at the image and compares the colour and brightness of each pixel with those of the pixel next to it. If the colour and brightness are much the same the information from one pixel is thrown away and the software simply remembers the location of two pixels, each with the same colour and brightness. The amount of difference between two pixels that is needed before information is discarded determines the 'quality' of the jpeg file. High quality jpeg files throw away less information than low quality files. The information thrown away cannot be recovered.
TIFF files are very similar to jpeg files, except they remember the colour and brightness information of every pixel, regardless of how similar it may be to those around it. A TIFF file can be regarded as the largest possible jpeg file, and the amount of information thrown away by a jpeg can be worked out by looking at the jpeg file size against a TIFF file of the same data.
Logically, the best images should come from TIFF files, and get progressively worse as the jpeg quality decreases and more information is thrown away.
Here's the full frame of an image from my Olympus C5000,
and here are a series of crops taken from pics shot in TIFF, Super High Quality and High Quality modes. Each crop shows an area from the very top of the small tree at 100%. This gives lots of edges, where the thin branches cross the grass of the field, and edges should be where jpeg files struggle the most.
It's possible to see an increase in quality from the HQ file to the SHQ and the TIFF file, but in a normal size print this difference just wouldn't be visible.
The original TIFF file is 15Mb, the SHQ file is 1.5MB (Which means 90% of the information in the TIFF has been thrown away!), and the HQ file is 0.9Mb.
Moral? I use SHQ and don't worry about it any more, except for those very rare times when even the last scrapings of image quality are useful - which means I can get almost 200 shots on a 256 Mb card, and enjoy the full four-shot buffer of the camera. Recording TIFFs freezes everything for about 10secs whilst it processes all the data and transfers it to the card.
RAW
RAW files are the raw data recorded by the sensor. To view them they need to be processed exacly like a jpeg, including all the interpolation of image size, sharpening, colour saturation and contrast adjustments. The difference is that RAW files can be processed at leisure on your computer, where you can adjust each of the settings instead of relying on the image-processing parameters buitl into your camera. The RAW file is not altered in any way during processing.
The main benefits of RAW are a small increase in image detail, the opportunity to set the colour balance afterwards (Which is probably the major plus point for us underwater photographers), and the ability to rescue slightly over and under-exposed shots.
Detail: Here's a busy shot I recorded in RAW and high quality jpeg with my Canon 350D:
100% crops from the centre of the image:
There's a clear difference, but in a normal print it wouldn't be as obvious.
Colour Balance: This was taken at 35m in the Red Sea using just available light and recorded as both a RAW and a jpeg. After running through Photoshop these are the best results I can get for colour - bear in mind that at 35m there's very little red about so even setting a manual white balance doesn't help much:
