How to Reverse Engineer Light

I’d like to teach you how to reverse engineer images, as it’s a really useful skill, and it’s particularly applicable to lighting.

Reverse engineering is a term in general use that means taking a finished thing apart, and from that, learning how it was made so that you can rebuild it yourself. In photographic terms, this means looking at an image, and deconstructing the lighting and techniques that were used to make it, so you can go and shoot something similar.

Reverse engineering is really useful on 2 levels. First, it helps you learn how other people work, and from there broaden your own skill base and hopefully create better work. Secondly, if you start to shoot any commissioned work, you’ll often find that clients bring you images before the shoot, and say “We want it to look a bit like this”. With skill in reverse engineering, you can then work out how to approach the shoot, what equipment you might need, along with what locations, subjects, props and so on.

Reverse engineering can be a bit like disappearing down a rabbit hole, and I should warn you that once you start examining other people’s images closely, you may find it hard to stop! I’m just going to talk to you about reverse engineering lighting in this video, as obviously that’s what the course is about, but you can also discern things like what sort of lens was used, and even start to spot how much an image might have been worked on in Photoshop! For now though, let’s look at the visual clues in an image that will help us work out how it was lit.

So what are the clues that will tell you how an image was lit? The simplest way by far is to look at the highlights, the shadows, and the transition between them. These alone will do a lot of work for you, even before you get onto more nuanced things.

Much of this is very obvious, but it still needs saying! The part of an object that faces the light will be brighter, and as such we consider it a highlight, and the part of an object which either faces away from a light, or is hidden behind something, will be darker and therefore in shadow. The speed with which the light transitions from highlight to shadow will give you an idea of how hard or soft the light was. If the transition is very abrupt, then the light was very hard, and if the transition is very gradual, then the light was soft. The same goes for the outlines of any cast shadows – a hard outline implies a hard light, and vice versa.

The length of the cast shadow will give you an idea of the angle of the light source – think of how small your shadow is under the midday sun, vs how long it is at the end of the day. The number of shadows is also a big clue – each light source will cast it’s own shadows, so there should be a matching number of shadows and lights.

On particularly smooth surfaces, such as glass, or mirrors, you may actually see exact reflections of the light source, and you may also be able to make out “catchlights” in a subjects eye. Both of these will show you where lights were placed in relation to the subject, although some photographers retouch them out, and most professionals go to great lengths to prevent them appearing.

Thinking about quality, the biggest indicator of quality of light we’ve already mentioned – how rapidly the highlight transitions into shadow. Don’t forget, a sudden transition comes from a hard light, and a gradual one from a soft light. The depth of the shadow can also be a clue, but quite an elusive one. How dark a shadow gets is not just a result of how hard or soft a light is, but what conditions the shadow area is in. Think back to what we talked about with dynamic range, and picture the scene if we were to point a hard, flash light source at someone. The transition from highlight to shadow would be very dramatic, and we might also assume that the shadow itself would be very dark and deep. This may not be the case if a reflector was used, as this will “lift” the deep shadows. You can even turn this on it’s head – a very soft light will cast quite subtle shadows, but if you were to surround the shaded side of your subject with black or dark surfaces, then the cast shadows would get deeper. Beware of falling into the trap of thinking “hard light=deep shadows/soft light=lighter shadows” as these can be played around with a bit.

Moving on to quantity of light, this is not always the easiest to spot, but don’t forget that with more light, you can choose a faster shutter speed/smaller aperture/lower ISO. Sometimes the quantity of light might be obvious – a night time scene for example, but beware that clever photographers can often manufacture a mood. Think about the creative effects of varying the three exposure aspects, and then look for them in the shot. At one end of the scale you might have a shot of someone jumping in mid-air, frozen perfectly without a trace of movement. The entire shot is sharp from front to back, and when you zoom in nice and close there’s no evidence of any noise. So, this would have been shot with a fast shutter speed, a small aperture, and a low ISO, all of which means there was probably a lot of light about.

Turn this on it’s head, and if you can see streetlights glowing in the shot, or household bulbs, or a roaring fire, you know there wasn’t much light around. Likewise, if there’s identifiable movement blur in an image, or even visible noise, then you can probably guess that not much light was around. Be careful using depth of field as a clue – it’s not just affected by aperture, but also lens focal length, sensor size, and camera to subject distance.

Lastly, look at the colours in an image. If the white balance was set correctly, and there was only one colour of light on the scene, there shouldn’t be much in the way of colour shifts, but be on the lookout for different colours in the shot. These may be “natural” colour shifts, and coming from mixed lighting, or “artificial” from the photographer’s use of gels.

So, now you know what clues to look for, in the next two posts we’ll examine a few images in detail.

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