Last week, I was in Cozumel, and one of the divers on the boat had a small Canon camera, a Canon SD-1000,(approx $30) which is an older model that I also own, and it always took great pictures. The diver asked me “why is it that even with the “underwater” setting, my pictures are very blue.
The answer to this is that as light crosses a body of water, it loses the higher wavelength color (starting with red, orange, then yellow then green), so in the end, everything is looking blue and/or purple. As divers, we probably have all seen when a divers flashy pink or yellow fins, at a certain depth look a dull grey.
A lot of digital cameras have settings to adjust for the loss of warm colors (usually, an Underwater Setting), but this setting can only adjust, not make up for the absence of warm colored light at greater depth. In fact, most camera manufacturers recommend the use of this setting at 20ft and above.
If diving below 20-30ft or in poor light conditions, the Underwater setting will no longer provide good results. Adding a red filter in front of the lens (to bring warm colors back) or adding artificial light (with flash or strobe) are the best options. Indeed, my fellow diver on the boat was very happy when I pulled a red filter from my dive bag and affixed it to his camera (no-one needs to know that this was done with duct tape, so shhh). His pictures came up with full color and he was on his way to the local photo shop to buy a red filter (I suspect some more duct tape too).
For some Canon housings, there are aftermarket solutions to add a red filter, while for some others, the filter will have to be affixed with a rubber band type retainer. On the recent Olympus Tough series, the outside of the housing has a 52mm thread, allowing to place a 52mm filter or more commonly an adapter 52mm to 67mm allowing to place a very common 67mm filter.
Adding a strobe is probably the best option, at least for pictures of subjects within a few feet of the camera. Strobes range in price from lower power (around $300) to highest power available (around $1000). Smaller cameras do not require the most powerful strobes available. And here is why: beginners typically equate power with shooting a further distance out, but such is not the case in underwater photography. Shooting too far out will lead to loss of resolution (picture looks almost blurry and details are faded) and backscatter (particulate in the water reflecting light as dots). The most powerful strobes will not then really allow to shoot much further out, but allow to get wider coverage for professional cameras equipped with extremely wide angle lens. In the case of smaller, Point and Shoot cameras, the wide angle is limited (to approximately 28mm focal length) thus a lesser need for very wide coverage. So, a $300 to $500 strobe will do really well to bring color back to pictures taken within about 3 to maybe 4ft of the subject. This means close-ups of animals, fish portrait, reef pictures from close enough and pictures of divers at depth become all possible and the picture is not blue. The PADI Digital Underwater Photographer specialty is a good option for divers starting with a strobe to learn where to position the strobe and how to make sure the picture will be well exposed and composed in a pleasant manner.
One can of course use a filter (without the strobe) or a strobe, but what of existing pictures that are blue, or pictures that are taken without a filter and where the strobe could not reach far enough? These can be corrected with post treatment software, either entirely or at least to an extent that makes the picture a lot better looking. Software such as Adobe Lightroom (about $120 to $140), Olympus Viewer 3 (free with Camera) allow corrections of white balance, color, exposure, contrast, saturation and more. The new Photo editor which comes with Windows 10 also allows correction but to a more limited extent (still, the results are impressive for a freebie).
Top Image is unaltered; Middle Image is a retouched JPEG; the Bottom image is a retouched RAW format image:
During the PADI Digital Underwater Photographer Level 2, after the second dive, your instructor will guide you through the steps to correct pictures with post treatment software.