Dynamic Range and Contrast Control

OK, this isn’t really part of the 4 characteristics of lighting, but it’s an area where light can play a large part. Let’s talk about dynamic range and contrast control.

Lots of what we’ve been talking about concerns using lighting to create effects. We might want to light things a certain way to create a certain mood, or drama, or be flattering, or reveal texture.

All of those are great, but it’s better to think of skill in lighting as simply allowing you to create the look you want, which may not be the most exciting thing.

Often, your ability to light well will allow you to deal with high contrast subjects, and bring something called the dynamic range within the boundaries that your camera can faithfully record.

Dynamic range sounds very clever, but essentially we can think of it as how wide the range is from the brightest highlight to the darkest shadow in a scene. If you picture an overcast, foggy day, there won’t be much different between the brightest parts of the sky, and the deepest shadows of something on the ground. Come back to the same scene a day later when the sun is out, and the brightest parts of the sky will be many times brighter than the darkest shadows.

Dynamic Range

This is a problem because cameras can’t record as big a dynamic range as we think, and our eyes are generally more sensitive than our cameras. The numbers vary from camera to camera, but most decent cameras can record a dynamic range of something like 7 stops (from the deepest shadow to the brightest highlight) and our eyes can generally record somewhere in the region of 10 stops.

What this means in practice is that in scenes with a large dynamic range, such as this scene of a park on a bright sunny day, we’ve either got to choose which end of the scale we want to keep detail in – shadow or highlight, or add light in some way to bring the dynamic range down. Here’s a decent exposure that tries to balance shadows and highlights, we can see that areas that are broadly average, like the grass, look OK, but the brightest parts of the image, such as the sky, are very washed out, and the darkest shadows are very dense and black, with almost no detail in them.

We can expose to get some details in the highlights, but in doing so, the shadows will get very dark, 

or we can switch this round, and bring out details in the shadows, but the brighter parts of the scene will blow out and lose detail. 

We can use something called High Dynamic Range, which combines several different exposure into one image to bring detail back into both ends of the scale. 

There are a couple of problems with this though – first off, it works much better with static subjects like this landscape, and would really struggle if there was much movement between the different frames it was blending from – or if the image was portrait and the person moved! Secondly, although this is just my opinion, I always find HDR images look really artificial – with strange ghosting effects around edges like 

High Dynamic range detail

I find it better to introduce light into the darker areas in some way, expose for the highlights, or close to them, and then let the light “lift” the shadows. Essentially bringing the dynamic range down.

This can be done with an actual light. In this example a flash with a softbox attached was used to lift the shadows to within the same range as the highlight areas visible in the window behind the subject. You can see here what happens if we just take an exposure without the flash on, whilst still exposing for the scenery in background, as opposed to adding the flash:

Or you can lighten the shadows with a reflector with this example of Paula Radcliffe. Since I’m shooting straight into the sun, Paula’s face is in shadow. If I expose for her face, most of the background will be very bright indeed, and we’ll lose most of the atmosphere from the shot. Instead, by exposing for the daylight, and then bouncing light back onto her face with this reflector, we can bring the dynamic range back to a point where the camera can record detail right across the board. In this case, we’re using a hand held reflector, but you could easily use something like a convenient white wall. 

Dynamic Range

When you reduce the dynamic range in an image, you’re essentially lowering the amount of contrast. At first this can seem like a backwards step – contrast in an image can be very appealing, and give an image lots of punch. However, the golden rule is – it’s always easier to add contrast afterwards, than try and remove it. It’s very quick and easy to take an image with low contrast, and add contrast using something like curves in Photoshop, rather than try to bring back shadows that have gone black, or highlights that have blown out. Look how much better this image looks when we add contrast, 

versus this one when I try and reduce the contrast and bring back detail into the shaows. 

So, to summarise dynamic range, remember that your eyes can take in more than your camera can, so you’ll either have to choose between keeping detail in the shadows, or in the highlights. You can use lighting of some sort to reduce the contrast in an image, and don’t forget it’s easier to punch contrast up in post-processing than try to reduce it.

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