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Underwater photography - absorbing colours

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Category: Specialist

Underwater photography - absorbing colours - Alan Graham of AnD Creations wildlife libraries shares his experience at underwater photography in this useful technique guide

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Absorbing Colours

Obtaining consistent colour in underwater photography is a challenge, but there are answers& There are a number of infuriating problems with taking a camera underwater - not least, the serious expense of a suitable housing to keep the camera dry; and then there's the complex knowledge you must dig up about the effects on, or lack of, light.

The first of these is rapidly being addressed by the likes of Subal, Ikelite, Sea & Sea and other companies, who are bringing out ever cheaper and more user-friendly housings and accessories.



Artificially fan coral with blue water back light; depth 22 metres

Light!

Well, unfortunately, this is quite a different matter. Getting answers to niggly little conundrums just isn't easy. The vast Web should be positively blooming with advice, yet I fear that many photographers are unwilling to furnish us with such hard earned knowledge. An experienced underwater photographer once explained: 'It's a real hands-on kind of job.'
I think he was trying to say that you just have to get out there and hammer away at the questions; fiddle and tweak, and be prepared to invent solutions yourself. A degree in optical engineering wouldn't go astray, either!



Translucent, cleaner shrimp lets blue light through; depth 28 metres
 
Among other things, our company produces wildlife documentaries (AnD Productions). The extraordinary speed at which technology has developing in the video industry in just a decade has, however, not filtered down into the underwater world. The manufacturers' mind-set seems to be 'just bung the camcorder in a plastic tub and go shoot a shark, or something'. But what if you want to capture unlikely images such as algae, sea slugs or translucent shrimps - those lesser giants found under over hangs or reef drop-offs, at depths where light does funny things to your composition. Still photography has long had answers - but can video match it?In order to find out, we had to design and build our own camera housings to fit customized lenses and innovative technical specs. The higher the quality of illumination the better the chances of acquiring true colour reproduction. But we had gone for backup; superior cameras and lenses would insure superior acquisition for flexibility in post production should unforeseen problems arise.


Author in the blue with custom video camera housing; depth 16 metres
 
Underwater Video has two major drawbacks. Trying to keep a steady shot over time (especially in close up on a fragile coral reef) is physically and mechanically demanding. The other is white balance.

Here is a menace that still photographers with TTL metering don't necessarily encounter. If they are close enough to their subject and strobes (flashlights) are well positioned, they should achieve near true colour. The problem is, red frequencies of light get absorbed by just three metres of water. Red things turn brown, hence the deployment of lights. But the further you are from your subject the less comes back to you, the light cast cools by turning yellow. If you are near the surface then sunlight helps, but below five metres you are on your own. Blue/green dominates.



Left, cool yellow light around scorpion fish. Right, white light; depth 25 metres
 
No matter how close to the temperature of sunlight (5600K) your video lights may be, their cast will gradually cool with every centimetre you back away. Pure white light requires an equal mix of red, green and blue. White balance compensates for an off-white appearance by adding the opposite colour to that of the temperature of light reaching the camera to the entire image. Not red. The opposite of yellow is blue.

This may seem a tad peculiar. Here you are, floating in a tropical blue ocean, staring through a mask as if it were a giant blue filter. Red has been absorbed by this filter, and yet your camera wants to add more blue to re-gain white. (NB Temperate oceans are predominantly green).

Where everything looks blue at depth during the day, at night everything unilluminated is, of course, black. This helps; an on land white balance setting is satisfactory for most night filming distances up to two metres, whether wide angle or zoomed in. However, you can't use the same tactics during the day, even though in your head it would seem to make sense to do so.



Left, showing true shadows. Right, white balance compensation; depth 18 metres
 
White balance works across the entire image, somewhat like a blue filter. But during the day the ocean is already doing that to everything unilluminated by artificial means. So, in any mode other than macro you will disastrously over saturate the blue sea and all those subtle blue shades beyond one metre that manifest themselves on the reef or around your subject. And that may render the acquired material, completely unusable. Adjusting white balance underwater may sometimes give good results, but you are relying on a video monitor; there will be water between it and your eye; and your brain will be subconsciously colour correcting due to the mass of blue all around.

Trusting the camera is a classic nightmare for photographers. Moreover, with SCUBA, white balance is unbearably frustrating to set when you feel like Neil Armstrong in EVA.

There is the task of explaining to your skittish little subject that they should just hold on a sec while you stick this white slate up their nostrils and manually adjust white balance. With only about 30 minutes of actual shoot time available below 20 metres depth and with the task of finding the critter required, setting up lights, camera, tripod, stability, buoyancy, etc.., you rarely get more than five minutes on the job in any one dive.



Macro of tiny pipefish head on, eye to eye approx' 4mm; depth 12 metres
 
Solution
Plan B. Lock white balance on the daylight setting, have a nice dive, and leave the colour problems to post production. We use firewire to download Canon XL1 digital video to the computer's hard drive. And edit the material using Adobe Premiere and Adobe After-effects software. On playing out to a TV monitor we saw the problem we had anticipated - continuity. In a magazine you can pass your eye from one image to the next, subconsciously aware that the camera has changed venue.
 


Left, wide angle of snake eel at 1/2 a metre. Right, zoom in from 1 metre
But in a sequence of video clips of one subject, clips must remain true to each other, throughout. The camera operators could not possibly keep precisely the same distance from the snake eel as it crept across the coral reef. Nor could one possibly get the close up white balance equal to the other's wide-angle white balance of the same species; filmed on different days, at different depths and probably at a different time of day.

Digital filters could be used to achieve continuity but they are too time consuming. Each clip in a sequence (carrying around 5Mb of info per second) requires a different degree of attention. To make the simple adjustments and eyeball accountability needed we would probably only manage a one minute sequence by the end of the next century. We found the solution in RGB Level controls.
 



Soft coral in wide angle (macro insert), shows differences in colour balance
 

We had gone on location knowing we might need some magic, but not with the intention of altering reality or adding to the scene; we were subtracting, letting reality emerge. In effect, we were getting rid of water between the subject and the lens, so that each clip had the same consistency.

How? We selected a single shot in each sequence that appeared well balanced - usually a close up. Then we applied highlights in the blue channel only, to any subsequent clips where light cast looked perhaps a little cool or yellow. The blue ocean was relatively untainted, shadows remained true, only the area affected by light cast was shifted back toward white.
 



Area below scratch line is treated. Above line is original; depth 18 metres

One day there will be a quality video camera designed specifically for use underwater. Until that time, you may wish to trust your computer to find the white light!

This article was written by Alan Graham of AnD Creations wildlife libraries. Visit www.andcreations.co.uk for your source of high quality still and moving images; supplying producers, publishers and advertisers.


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