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Explanation On Why Snow Can Appear Blue And How To Fix It

Explanation On Why Snow Can Appear Blue And How To Fix It - John Gravett shows you how to make sure every snow-scene shot you take is as white as the real thing.

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Category : Landscape and Travel
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Words and images by John Gravett - www.lakelandphotohols.com

We all know the feeling of photographing in snow on a bright, crisp day, only to realise that the snow is coming out blue in your pictures. This is generally due to one or two errors which can be quickly and easily put right – preferably at the taking stage, but failing that, in Photoshop or Lightroom.

Because your camera's meter is calibrated for a scene of "average" brightness, photographing a snowy landscape can often lead to underexposure, by seeing the white snow as a mid-tone. Even those cameras with RGB sensors in their meters will still underexpose snow a touch. Invariably this will leave the snow either a dull grey on your photo, or, if you're shooting under a blue sky, you'll end up with blue snow. The other time when snow typically shows a strong blue cast, is when you are photographing in the shade on a sunny day, under a blue sky; when the snow is only receiving light from the sky itself.

Wind Farm
Wind Farm - Shows underexposure and a strong blue cast on the snow.

So, firstly – exposure:

Remember, because most meters are calibrated to a mid-grey, the camera will tend to UNDEREXPOSE the snow, so either take a meter reading from a grey card (or neutral tone), hold the AE-L button to lock your exposure, recompose the picture and take the shot, or – more simply, use your exposure compensation to increase the exposure to change the snow to a bright tone; depending on your camera and metering system, this can need from +0.7 stops to +2.0 stops compensation.

+1 Stop Exposure
Wind Farm taken with +1 stop compensation.

Once you've taken the picture CHECK YOUR HISTOGRAM – to make sure the highlights are to the right of the histogram, without blowing details.

Secondly, colour cast (blue):

As we said above, blue snow in pictures occurs where the snow is receiving no direct sunlight, but is simply being lit by sun reflecting off the blue sky (hence the cast!). Underexposure from the average meter reading will make the cast worse, but it can be easily corrected.

Most photographers who visit me for the first time have their cameras set on Auto white balance (which won't generally get strong colour casts right at the taking stage). The extreme blue cast can easily be corrected in camera by either setting the white balance at shade (which equates to about 7000°K) or by taking a preset / custom white balance from the snow. Either of these techniques will give a neutral tone to the snow. So many photographers say to me “As I shoot RAW files, I don't need to worry about it at the taking stage, I can just sort it out in the computer later”. Personally, I'd sooner get it right in the camera and spend less time correcting casts in front of the computer, and more time behind the camera taking pictures.

Of course, if you're photographing snow in the sun, it will generally be a pure white when correctly exposed, at, say, sunny white balance. Shadows on the snow in the same picture will still exhibit a strong blue cast. Correcting the cast of these shadows at the taking stage will result in a strong yellow cast on your sunlit snow. Personally, I just leave these blue and the sunlit snow a crisp, pure white.

So what can you do to correct the blue tint to the snowy pictures you already have? If they are shot at RAW files, you can – of course – change the white balance to Shade, which will usually get the colour about right. If you have shot it as a jpeg, a little more work will be needed in colour correction. Try adding a levels adjustment layer and taking the mid-tone slider on the blue channel down to about 0.8 (from 1.00) and perhaps changing the red mid-tone from 1.00 to around 1.05. If you want to reduce the strength of the blue cast in the shadows, try adding a selective colour layer, or hue and saturation layer, and adjust the blues only.

Wind Farm

The windfarm exposed as per meter reading on daylight white balance shows underexposure and a strong blue cast on the snow. With +1 stop compensation, the exposure is better, but there is still a blue cast. By changing the white balance to shade (7000 deg K) the blue cast is eradicated (shown above). The same is shown on the snowy textures, where the daylight setting (5000 deg K) shows a very strong blue cast, but the shade setting renders the “blue” snow white.

Snow - sunny
Above: Taken on the daylight setting
Snow - shade
Above: Shade setting renders the "blue" snow white.

The greatest problem comes with the sign, where the background is in direct sunlight, but the foreground is in shade, in this case, the extent of blue snow was more than I really wanted.
Adjusting White Balance
I therefore shot the picture on daylight colour balance, changed the RAW file to "shade". This corrected the blue snow but made the sunlit snow and bracken far too yellow. I then opened both versions in Photoshop, layered them into one picture and with a layer mask, created a picture with daylight balance at the top and shade balance at the bottom (third image).

So taking a few careful steps this winter should keep your snow bright white – even in the shade.

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Comments


12 Dec 2012 2:53PM
Hello,
another effective way to correct the blue cast is, in Lightroom, to desaturate the blue in the HSL panel as far as the sky doesn't appear in your image !

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