Colour restitution in available light underwater photography
By Jose M. Romero Bellido (Area 3+)
Among the special limitations that the underwater environment imposes on photography, one of the most important ones is the selective colour absorption that takes place as light passes through water. This absorption starts from the red end of the spectrum; it's generally said that red colours disappear between two and five meters of depth (though we'll comment about this later), and succesively do orange and yellow. Besides, this absorption of colours occurs both vertically and horizontally, so it depends not only on depth, but on the viewer-subject distance as well.In order to solve this problem and get "natural" colours, the use of a flash is always offered as the only practical solution (it's also possible to experiment with colour correction filters, but their usefulness underwater is very limited). However, although it's never mentioned in books or articles on underwater photogtraphy, there's also another option: to correct the colour in the photographic darkroom. So, from a slide taken exclusively with natural light (with daylight film and normally processed) it is possible to obtain a colour-corrected duplicate.
It must be emphasized that the loss of colour doesn´t happen suddenly, but gradually. Red, for example, doesn't completely disappear at five meters, as we´ve said before. Actually, at ten meters there's still a small percentage of red and orange wavelengths, approximately ten percent, which will be captured by the photographic film. These small amounts of red and orange may not show in the slide when viewing it at first sight, but when we eliminate in the darkroom the intense blue cast that hides them, it is possible to "amplify" them and make them visible.
Basically, it's a question of doing something that is more or less common in "land" photography, such as duplicating a slide to correct a wrong colour balance or exposure error, but here the change must be much stronger; and, according to my experience, the standard materials and processes used to obtain duplicate slides or prints (on reversal materials or with an internegative) are not suitable at all for the special characteristics of underwater images. However, modifying the standard processes and using some special techniques (that, by the way, does not include digital imaging) it is possible to improve colour as well as other aspects of the image, such as contrast, for example.
I must point out that my aim when making the colour correction is not to restitute any particular colour "at any cost", but to achieve a colour balance as natural as possible in the scenario. Precisely, one of the most important advantages of this system, from my point of view, is the ability to achieve natural colours and depict the "atmosphere" that divers see, something normally missing to some extent in photographs taken with flash (though this may be a matter of personal taste, as well as in "land" nature photography some photographers use flash and others never use it). There's also the possibility to combine both techniques, if one doesn´t want or can do without using the flash (to fill-in shadows or in low-light situations, for example); in that case a blue filter should be placed on the flash (as recommended by Kodak for their Ektachrome Underwater), so that it´s possible to adjust the colour correction for the area in the picture that doesn´t receive the light from the flash, but the filter prevents the area that does receive it from getting "overcorrected" (that is to say, too reddish).
At the time of planning to make use of this colour correction system, as a guideline we could say that, the bigger the difference between the colours in the original scene (just as we remember having seen them underwater) and the colours that show in the slide, the more spectacular the colour correction will be. Or, as well: when the colour in the scene that we contemplate underwater is appealing to us, though our experience tells us that we´ll get an excesively blue slide if we take the photograph with natural light only, nevertheless it will be possible to get from this a duplicate slide (and its corresponding print on paper, if we wish) with its colour surprisingly corrected.
In order to show the degree of colour improvement that it is possible to achieve, this article includes several photographs taken in Cuba, with a Nikonos V camera with a 35 mm lens, and snorkelling (I mention the latter because I think that the possibility of getting good results photographing without flash is specially attractive for snorkellers). Two versions of each photograph are shown: the standard or "bluish" version, i.e. the one obtained directly when photographing without flash, and the corrected version, obtained from the first one.
Photo Nr. 1: strange as it may seem, this photograph was taken very close to the surface, maybe between one and two meters. It was really surprising to contemplate the lack of contrast and colour in the original slide; perhaps taking the photograph with the camera pointing slightly downwards exerted an adverse influence, although in such favourable conditions of depth, luminousity and colour it was difficult to imagine a result like this. Experiences of this kind probably have convinced more than one underwater photographer about the impossibility of getting photographs with vivid colours if one doesn´t use the flash. This would be an extreme case of what we've said before about that, the bigger the difference between the colours seen underwater and the ones reflected in the slide, the more spectacular the colour correction will be.
Photo Nr. 2: the depth here is somewhat bigger, between three and four meters. Theoretically, it would be the zone recommended as the limit for photography without flash; however, once again the look of the original slide is too poor, according to what is seen underwater. With regard to the corrected picture, in this case a degree of contrast has been achieved that makes the fish and their yellow tails stand out from the background.
Photo Nr. 3: this photograph was taken at eight meters of depth, clearly surpassing the limit recommended for available light underwater photography. However, the correction achieved is remarkable, responding to the sense of luminousity and colour perceived underwater. To mention a significant fact, looking at the coral in the foreground one can notice (when the image size is big enough) some small red areas, while, as we´ve stated before, it's generally said that red disappears between two and five meters of depth. And a comment that is also applicable to the previous pictures: not only the colours of elements in the foreground have been corrected, but the blue in the background looks "bluer" as well.