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Night poses special problems for colour photography. It’s not the level of illumination that’s the problem, but the colour of the lighting. If you shoot in a busy city centre, you may have a mixture of tungsten lights, fluorescent lamps, yellow/orange street lamps and even multicoloured neon. How are you supposed to reconcile all these with a single white balance setting? Our advice would be not to try. This is one situation where your camera’s auto white balance should just be left to get on with it. Only if the colours look completely wrong should you worry about taking over manually.

Different light sources

Its not possible to compensate for every single light source, and sometimes the colour of the light doesn’t fall neatly on the warm-cool colour temperature scale. White balance adjustments work by shifting the whole spectrum of the light source up or down the scale. They rely on the light having a full spectrum of colours, but simply shifted one way or the other. Some light sources don’t have a full spectrum of colours. The prime example is orange streetlamps. They look orange because that’s all there is — no blue, no green. It’s impossible to correct orange streetlighting to produce a full range of colours. Fluorescent lighting is the other oddity because it contains excess green. Digital cameras deal with this with one or more dedicated ‘fluorescent’ settings. These increase the levels of magenta (green’s complementary colour) to restore a natural-looking colour balance.

How to achieve a good mix

Where you have more than one type of light source in a night shot, you could try matching the white balance to this dominant lighting. There are two ways of going about this. You could judge the scene by eye, identifying what look like tungsten or fluorescent light sources and choosing a white balance preset to match, or you could use a ‘grey card’ to measure and save a custom white balance value. Actually, it doesn’t need to be a grey card at all. The important thing is that it’s neutral in colour, so a sheet of white paper would do in an emergency, or even a black and white magazine or newspaper page. You need to hold the card under the dominant light source, capture and store the white balance reading and then use this custom white balance setting for the rest of your shots. The best bet is to shoot in RAW mode (if your camera supports it) so that you can choose another white balance setting if your manual calibration doesn’t produce the results you want.

Photoshop Techniques

Although it’s generally best from a quality and even a visualisation point of view to get the colours right at the time of shooting, that’s not always possible. There may not be enough time, the equipment or the conditions might not allow it, or you may only see the Image’s true potential when you’ve opened it on your computer screen back at home. Here, then, is a selection of techniques you can use in Photoshop and (all but the Curves adjustment) in Elements too. Each adjustment has pros and cons, which we explain individually.

Colour Balance

Colour Balance adjustments can be carried out directly on the image or using an adjustment layer. You’re presented with three sliders — Cyan/Red, Magenta/Green and Yellow/Blue. Note that these are pairs of complementary colours. In our sample shot, our subject’s skin tones have a magenta tinge, so we’d counteract that by moving the Magenta/ Green slider to the right, which will shift the image’s colour balance towards green and away from magenta. You need to develop a good eye for colour casts to use the Colour Balance dialog effectively. For example, fixing our original shot effectively meant spotting that the unwanted tinge was magenta rather than red (which is what it looks like at first glance). For a more extreme effect, we can increase the Red/ Cyan to 100 and reduce the Yellow/Blue to -100. This gives the warm colours you’d expect from candlelight or firelight.

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Hue/Saturation

The Hue/Saturation dialog works in a subtly different way. The Hue slider shifts all the colours along the colour spectrum. This can solve some colour problems, but the effects can be unpredictable and hard to control. At the same time, you have a Saturation slider for increasing the strength of all the colours in the image. Our original image was shot on an overcast day and has distorted and flat-looking colours. We can try to boost the colours by increasing the Saturation level, but this also exaggerates the unwelcome red/purple cast in the brickwork beneath the ivy leaves. The solution is to adjust the colours independently. First choose the nearest colour from the pop-up in the Hue/Saturation ‘Edit’ menu. Then use the eyedropper to click on the part of the image you want to alter. Your hue and saturation changes will be applied to this range of colours only. Our final shot features ‘reddened’ brickwork and greener leaves.

Levels

By default, the Levels dialog displays the combined RGB values of the pixels in the image, but you can open the menu at the top to view and edit the red, green and blue colour channels independently. This explains the difference between applying Auto Contrast and Auto Levels. Auto Contrast maximises the tonal range without altering the ratios of the three colour channels. Auto Levels optimises the channels individually, which can coned colour casts, or introduce colour casts where you didn’t have any of Our original shot has a strong yellow cast because we used a coloured graduated filter over the sky. Simply applying Auto Levels restores a much more natural colour balance. In the final version, though, we’ve gone further by moving the red channel’s midtone slider to the left to make the colours redder, then gone back to editing all three RGB channels and moved the midtone slider to the right to darken the image.

Curves

Like many digital camera images, the shot we’re starting with looks a bit flat, even though the histogram shows a full range of tones. Our first attempt at adjustment uses an ‘S-shaped’ curve which darkens the shadows slightly and lightens the highlights but, because the curve is steeper in the centre section, it adds contrast to the midtones. Our final example is more extreme. It exaggerates the contrast in a specific tonal range — the red brickwork. The way to do this is to open the Curves dialog, then drag the mouse pointer (it changes to an eyedropper) over a critical area of the image. The tones at that point are displayed on the curve as you drag. This is the point on the curve where the curve gradient needs to be made much steeper. Note how increasing contrast also increases saturation. The two are inextricably linked, and if you sort out your image’s contrast properly, you’ll often find out you don’t need to increase its saturation.

Brightness/Contrast

Brightness/contrast adjustments are the easiest to understand, but they’re also the most destructive with regard to image quality. Why? Because increasing the contrast pushes dark and light pixels off the scale, so that shadow areas of your image become blocked in and highlight areas bleach out. You need to use the Brightness/Contrast dialog with care, then. If you display Photoshop’s Histogram palette while you work, you’ll see what we mean. The image we’re starting with is rather light and lacking in contrast, so our first attempt at repair is simply to reduce the Brightness value. This looks OK superficially, but the histogram shows the highlights are no longer a true white, and a lot of shadow detail has been %lipped’. Increasing the contrast strengthens the colours (remember the link between contrast and saturation), but yet more shadow and highlight detail has been lost.

Taking it further

The colour adjustments we’ve looked at here have largely been aimed at correcting or enhancing colours. But many of the techniques can be adapted to produce more extreme colour alterations. Using Photoshop, it’s possible to mimic many of the effects once generated in darkrooms, including solarisation, sepia-toning, cross-processing and more. Indeed, with a little experimentation, it’s possible to come up with effects never seen before — and sometimes effects you’ll never want to see again… Apart from the Ideas we introduce here, you can try out Photoshop’s different layer blending modes, either blending two images together, or duplicating the current image layer then changing the way it interacts with the layer below. Don’t just stop with a single modification or filter, but try combining them. There are so many permutations in Photoshop that you may never exhaust them all.