Snow exposure explanation in detail

I've talked about how we have to trick the in-camera meter to deal with snow scenes before, but it is worth reviewing at times.

Remember that the meter is trying to make the value of the scene 50% grey, whether it is looking at a pure white scene or a pure black scene.  Try shooting a white card and a black card to prove this to yourself.

What that means, then, is that if you are shooting a snow scene, you have to increase the exposure so instead of the snow being grey, it comes out close to white.  I say close to, because we want to hold some detail so we do not want the values to go to 255 (pure white) in Photoshop.

What I suggest is using the exposure compensation feature of your camera, and add about 2 stops of exposure to make the scene work.  Check your histogram to make sure you haven't lost detail.

Now let's see what happens once the image comes into Photoshop for tweaking.  Here's the image as it was processed from the raw file.  Notice that I have made sure not to let the sky or foreground go pure white.

Here is the histogram for the file.

 

Now we'll use a Levels adjustment layer to brighten the whites, and make the dark values richer.  Be careful here because since it was a snowy day with low clouds, there shouldn't be a pure black.

I like to use adjustment layers rather than Image-Adjustments-Levels from the Toolbar because you can always tweak what you have done later with adjustment layers.  They sit as a non-destructive layer about the image in the file.  With the Toolbar approach, you cannot go back once the adjustment is made.

Take a look at the values for the lightest and darkest spots in the photograph.  I used the eyedropper tool to identify them.

Here are what the new values are in the Info tab of the Navigator window.

And here is what the final image looks like after the adjustments.  Keep in mind that seeing the subtleties online at this size is a bit challenging.  Try working on a file like this, and you will see how well this approach works.

Exposure Compensation in Snow

As a more detailed explanation of the need to compensate when shooting in snow, here’s a good example.

Remember that all light meters give you an exposure that would place whatever is covered by it as 18% grey. So if the scene is mostly snow, the exposure will be underexposed significantly. The solution is to use the exposure compensation feature of your camera. On a point and shoot, it may be a little button you push on the back of the camera, and then rotate a dial. On a DSLR, like the Canon 40D the shutter button pushed half-way down, you simply rotate the dial on the back of the camera.

If you are shooting with film, you can start with a minus one stop setting and bracket a stop in each direction. If you are shooting with a digital camera, simply check your histogram to make sure the highlights don’t blow out. Experience will help guide you once your done this a bit.

Above is an example of what happened by just letting the camera decide exposure in shutter priority mode. The accompanying histogram below shows loss of detail in the shadows (whenever your histogram butts up to the left edge), and that the snow will appear grey (the highlight value is far away from the right edge).

Now here is an example increasing the exposure 2/3 of a stop. Notice in the histogram that all the shadow detail has been held, and the highlight values have increased to make the snow near white.