BLUNDERS OF BLACK & WHITE
Despite the invention of colour film and digital cameras, monochrome photography has never lost its appeal over the centuries. I dare say it never will. Black & white photographs have a subtlety and unnatural appearance, often resulting in a timeless charm with dynamic visual impact. The absence of any hues enables detail and texture to be emphasized in a manner that would look quite garish in a colour image.
For the amateur photographer, a black and white photograph is merely a de-saturated image. The same lack of forethought and experience that goes into taking the pictures is reflected in their post processing too. This usually involves opening up their RAW files in the editing software of their choice and simply pulling the saturation slider to zero. Voila. Job done. Finito! The outcome, more often than not, is a drab, non-captivating collection of pixels, that lacks depth and definition and visual impact. I'm not bashing beginners here, just pointing out the realities of photography and editing.
The problem is two fold. The first is quite obvious. The lack of colour information in a black and white image, means that only grey tones remain. In order for our eyes to disseminate different areas of a photograph, we need contrast between them. In the below example you can see red and cyan blocks. The two are easily identifiable from each other with a clear dividing line. Note the green arrow on the saturation slider is at 100%. The image changes to show the exact same blocks with the saturation slider at 0%. As the colour information disappeared, so too did the definition between them.
Although separate areas of a photo have completely different colours (the above two colour blocks are at 180 degrees from one another on the colour wheel), if their saturation and brightness are equal and only the hue differs, when we desaturate that, all that remains are equal grey tones. While this is highly unlikely to occur in a photograph, if the values of saturation and brightness do not differ from each other significantly we are left with a very flat histogram and a correspondingly bland image.
The above example is very basic but, imagine that the background was all red and a sentence was written upon it in cyan, or any other colour with the same saturation and brightness values. The information is there when the hue is present, it's invisible once desaturation has occurred.
To counteract this flatness, we need to increase the contrast. This can be achieved in numerous ways. If you're using Adobe Camera Raw, then the first step may be to raise the contrast slider. Other options include boosting the clarity slider, lowering shadows and blacks and lifting highlights and whites. The further we push the pixels away from the centre of the histogram towards black and white (or away from one another), the more contrast in the image and greater the visual impact. Inside Photoshop itself, this can be expanded upon and directed to specific areas of the image with the use of dodge and burn tools/techniques.
Comparing the two images below, you can clearly see what the effects of constricted tonality are on black and white photographs. The left hand picture has significantly less depth both in the face and separation with the background. The ambiance is also lost when the shadows and highlights aren't present. As a result, the right hand image has significantly more visual impact to the viewer.
The second problem occurs at the time of capture. Specifically it's to do with light and it's positioning. Lets say you are taking a portrait of a model and illuminate them with the pop-up flash on the camera. The light from the flash is hitting them at 180° degrees and bouncing straight back towards the sensor. The light is regarded as flat. No shadows will be cast upon the face if they are looking directly at you, only the wall behind (that's if you even have one).
Now before I get a flood of emails, yes, you do see variations of "flat lighting" utilized in the world of fashion and beauty photography with the specific aim of reducing skin texture and blemishes. However, the light while parallel to the camera, is generally above the subject so that shadows are still present under the eyebrows, nose and chin (although frequently lifted with reflectors). The only exception is when ring flash is used to give a distinct look. Other than that, you will rarely see a professional portrait/fashion photographer using the pop-up flash. If you do it will be as a minor fill or triggering off camera flashes using Nikon's Creative Lighting System (CLS)
In general, flat lighting is something to be avoided because, particularly with monochrome images, as it gives us the most humdrum lighting possible. Even in a colour photograph. When you desaturate the image, the lack of contrast in the skin is exacerbated further because, as with the previous diagram, once the hue information is gone, just a solid block of grey remains.
The solution is to get the light source off camera, so that you create highlights and shadows, which give your images depth. Whether you opt for window light, a lamp or strobe, it matters not. Just so long as you get that range or tones into the image, you will be able to get good monochrome images from your colour photographs.
If you're planning to do a black and white photographs before shooting has even commenced, make sure your lighting isn't flat to the subject. Ensure you introduce contrast by positioning your light at different angles and heights (see the lighting styles guide for examples). Also, aim to use smaller modifers, as they are naturally more contrasted and will produce darker shadows. The resulting images will be much more dynamic and eye catching. If shooting outdoors on a grey day, you will have also flat light, as it's omnipresent. Overcome this by tunnel lighting your subject (place them in a doorway or under on the edge of a roofed, open-walled structure) or introducing your own light with off camera flash. A silver reflector can also add more specular light onto your subject to just lift the face.
So next time you're either intending to shoot or later convert your work to black and white, think about your lighting specifically (not that you shouldn't do that anyway). In post production, don't just simply reduce the saturation. Play with the sliders in your editing software to boost global contrast and then target specific areas within to boost local contrast. Bring out the details, texture and shape. Your photographs will thank you for it!