Exposure Compensation AWT3 jmartin
The Problem
How many times have you gone out on a nice sunny day and taken a picture that ends up looking strangely dark, like these ones, shot on a sunny beach and looking out a sunny winter window?
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I just let my light meter do the exposure automatically. It's usually pretty reliable, so what happened? (This refers to the beach picture) :
- The light meter usually takes an average of the whole scene, but there's a high contrast between the bright and dark areas
- Lots of the pic is in full sun, and highly reflective: the beach, the rocks, some of the skin & clothes
- This makes the meter think there's a lot of light overall, so it exposes less (smaller aperture and/or faster shutter)
- The bright parts of the picture are well exposed, but the shaded parts are very underexposed
- We're most interested in the faces. They're underexposed, so we feel (correctly) that whole picture is dark, even though on average it's not.
What to do?
A: Try to correct by brightening the levels in Photoshop? Not Great…
The Levels and Dodge tools let you lighten the image. If you try to lighten very dark images, you'll find they do look brighter, but:
- the dark areas get very grainy & "noisy" as you lighten too much
- the highlights (already light areas) get overexposed - washed out, like the rocks and the bright parts of the skin
B: Make sure there's good light on faces and other important areas when shooting in high contrast situations? Better, if Possible…
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With her face tilted into the shade, the young woman (my
niece, in the freezing
C: Take the Light Reading
If you can, set the exposure when holding the camera close to the part of the subject you want exposed correctly. But this is often hard to do, so…
Most digital cameras have a way to compensate for incorrect exposure. It's your way of saying to the light meter: "You think you know how to expose this shot, but I know better, so I'm going to add or subtract a bit of light from whatever you think is right!".
The control is sometimes buried in a menu (and only available in modes like "P" where you get to mess with settings). On other cameras there's a button and dial or cursor keys to change it. Usually it's shown as a little scale, with 0 in the middle, -2 on the left and +2 on the right. Setting to the left means you will get less exposure than the meter calls for; to the right exposes more.
Here's an example, a rare sighting of the Eastern Wood Plover-on-a-Stick!
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Exposure
Compensation: 0 The snow is perfectly exposed – deep shadows, lots of detail, but the bird is pretty much just a silhouette. Maybe this is what you wanted, but not if the bird's colouring & plumage (okay, her paint!) are what you want to show. |
Exposure
Compensation: +1 Now the snow is slightly overexposed, but you can still see good detail. The bird's detail and colour are fairly good. This is likely the best compromise. |
Exposure
Compensation: +2 The snow is highly over-exposed – we only see a washed out field of flat white with a only bit of shadow, none of the rich detail On the other hand, this is the best exposure of the bird, if that's all we care about. |
As you can see, exposure compensation is useful, but usually involves compromise. Do you want to overexpose the highlights the for the sake of the shadows or have dark shady areas but well-exposed highlights?
If possible, try to avoid this dilemma by setting up your shot to avoid high contrast. Overcast days are better than sunny ones because of this.
Or, if the background is bright, compose so your subject is also in fairly bright light. Here's the Plover shot with the sun behind the camera:
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Exposure
Compensation: 0 |
Exposure
Compensation: +1 |
The lighting is less dramatic, but both the snow and the bird are well exposed.
Under-exposing
There are a few situations where you'll get a better result if you use Exposure Compensation to reduce the exposure from what the meter wants.
Shooting sunsets and clouds are two examples.
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Left Image: Even though the light was fading, the meter brightens the image by opening up the aperture and slowing the shutter speed. A bit of cliff detail is visible, but the water's colour is not as vivid as it actually was. Right Image: Less exposure blackens and sharpens the cliff. The colours in the sky and especially on the water are much richer. Ah, summer! |
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Exposure
Comp: 0 |
Exposure Compensation: -2 (Also, I was also shooting at an angle more into the sun, so the meter thought it was brighter and therefore lowered the exposure) |
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Case Study
What's the "right" exposure for this image?
The answer is, "it depends…"! Because much of the image is in shadow on a bright snowy day, you have to compromise. Do you want the viewer to study the darker details of the the boulder, or concentrate more on the shapes and lines of the overall composition? Decide whether you want to see detail in the highlights, mid-tones or shadows, and set your exposure compensation accordingly.
Here's a composite of 4 exposure compensations, from -1 on the left through 0, +1 and +2:
None is absolutely "correct"…
The darkest exposure is great for the snow and sky details, but lacks colour and details in the shade. The brightest shows the colour and lichens on the rock and fence best, but the snow, sky and tree are washed out.
It's all about compromise! (and about avoiding shots in harsh lighting contrast, unless you know that you can sacrifice either the darks or the lights).
p.s. Back to the Cat…
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By now you should know the problem: too much back lighting fools the meter into thinking there’s lots of light, so it lowers the exposure. That’s okay for the snow, but tragic for the poor cat, unless he wanted a silhouette. |
By setting the highest exposure compensation (+2), the cat is exposed better. However, the fine detail of the whiskers against the snow is washed out, making it look like a bad cut & paste job. Bottom line: avoid shooting with really bright back-lighting, as in shooting someone who’s indoors with an sunny window in the background, unless the sun also illuminates their face, or you want a silhouette. |
