A very interesting discussion going here. My take on the subject is that the colour management used to render a bird photograph depends on the purpose for which the image was created. If it is your intention to create an image with the colours of the bird looking something like the reference images we find in ABG, then you will usually need to make some lighting adjustments like those suggested by a number of contributors. These adjustments are in effect trying to produce an image of the bird like it would appear with ‘standard’ illumination. Historically, the standard illumination used by ornithologists and scientific illustrators when describing and recording the colours of birds is what we loosely call daylight or its equivalent. An important function of the BLP image library is to provide reference images enabling users to identify birds, ideally to the subspecies level, to show any sexual dimorphism, breeding plumage, plumage morphs, moult stages and age classes. To meet this objective we need to produce images with reasonably accurate colour rendering. What I have to say in this post is all to do with trying to achieve accurate colour rendering in the sense just described. In writing this I am well aware that we create bird photos for other purposes which are just as worthy such as giving priority to what some photographers call ‘capturing the light’; an obvious example of this is warm images captured during golden hour.
The aim of this post is to providing more practical advice and examples of how to accurately render a bird. One of the main difficulties is that we are dealing with multiple light sources. Even on a clear sunny day we have one primary source and one or more secondary sources making a contribution to the illumination of the bird. The different sources have different spectral characteristics from warm to cool (colour temperature). We can adjust for this using the amber-blue white balance slider or colour temperature slider. Contrary to common belief, these two adjustments are doing the same job, you will get the same result whether you adjust the amber-blue slider or the colour temperature slider. A difficulty arises when part of the bird receives more illumination from one source than another part of the bird. The white balance adjustment is a global adjustment so we must choose which part of the bird has adjustment priority. We can end up with part of the bird having the correct white balance adjustment and part of the bird with a colour cast. To deal with this situation we will need to make colour adjustment on the part of the bird having the colour cast. A common example of this problem occurs in avian flight photography on a clear day when photographing birds with a dark top side, for example, most raptors and many petrel species. The main illumination is the direct sunlight and we use the appropriate daylight or sunny white balance pre-set. This usually gives a reasonably accurate rendering of most of the bird. However, the blue sky hemisphere above the bird is a secondary source of illumination and there will be a component of this light reflected off parts of the top side of the bird to the camera (specular reflection). If the bird has a dark top side, the blue sky reflection will appear on those parts as a magenta colour cast. When I encounter this problem I select the part with the colour cast and decrease the magenta and or blue saturation. A hue, saturation, luminance adjustment will achieve the same result.
A second example of where a single global white balance adjustment needs to be followed by selective area colour adjustment is regularly encountered in pelagic sea bird photography. Many sea birds have a convenient neutral white part on their top side, for example rump or crown, that is an effective spot to use for white balance adjustment. Some species have good neutral grey upper-parts that can also be used. They will usually be photographed flying over the sea and on a sunny day there will be a significant amount of light scattered up from the top few metres of water. This upwelling illumination is usually blue or blue-green and if the under-side of the bird is white, as often with seabirds, then a pale blue colour cast will be observed on these parts. Once again, the remedy for this problem is to make a selection of the affected parts and apply some desaturation of the blue channel.
There are other examples where multiple sources of illumination can cause difficulties similar to those already described. Without going into specific details, another common example is the green or yellow-green colour cast that can affect parts of birds having white under-parts when they are perched over green vegetation. Another example is seabirds having brightly coloured feet; light reflected up off their feet when the birds are standing can cause a colour cast if they have a white belly. A good examples of this are Gentoo Penguin and Red-footed Booby (white morph); what do you do in this case? Leave as is and make an appropriate comment would be perfectly acceptable.
Earlier in this thread I mentioned that colour checkers can work well as colour standards in some situations. In my experience, colour checkers are most useful at set-ups, for example at a bird bath. This kind of set-up can be regarded as a kind of outdoor studio but with one important difference, the ambient light usually changes during a shoot. This can be ameliorated if the colour checker can be mounted close to the action in the same light and colour calibration shots taken a few times during the session. If this is not possible, the colour checker can be temporarily placed in the centre of the field of view at the beginning and end of the session to enable calibration shots to be taken. An average of the before and after colour checker values can be used to generate the working colour profile. The illumination of the bird at a set-up will usually be a mix of light from one of more flashes and the ambient light which will usually have a primary source and a number of secondary sources. I usually aim for about half the light to come from the flashes and use the white balance pre-set for flash and neutral picture style as the starting point for generating the color profile. The first step is to fine-tune the white balance using the neutral density panels on the colour checker and adjusting the brightness so that the measured neutral panel RGB values match the calibration RGB values provided with the colour checker. The next step is to use Hue, Saturation and Luminance (HSL) adjustments in your photo-editing software to bring the measured results for the RGB and CMY colour panels into agreement with the calibration values. When this is achieved to your satisfaction, the colour profile is saved as a recipe for use with the images captured during the session. RGB colour space and HSL adjustments for the colour calibration work well for modelling the output of physical devices like monitors and printers. An alternative colour space which also works is CIELAB which is designed to approximate human visual perception. The X-Rite Color Checker provides calibration data for both sRGB and CIELAB colour spaces.
