Daily Post: Snow Exposure Quandry

Pan Am 310 East of Shelburne Falls

I exposed this image of Pan Am Railways GP40 310 leading MOED on the afternoon of February 17, 2014. By any measure this scene posed a difficult exposure.

Canon 7D in-camera Jpg of Pan Am Railways 310 east of Shelburne Falls, Massachusetts. To my eye, this image appears too bright. Had it been a color slide I'd say it was about a half stop 'over exposed.' This Jpg was created using the Canon's picture style profile called 'landscape' (one of several built in Jpg picture styles).
Canon 7D in-camera Jpg of Pan Am Railways 310 east of Shelburne Falls, Massachusetts. To my eye, this image appears too bright. Had it been a color slide I’d say it was about a half stop ‘over exposed.’ This Jpg was created using the Canon’s picture style profile called ‘landscape’ (one of several built in Jpg picture styles).

The locomotive is a dark blue, while the scene posed a full range of tones from bright white snow to deep shadows. The train was moving, and there was little time for exposure bracketing.

Using the camera’s histogram, I’d made a test exposure before the train came into the scene, and then made a series of images focused on the composition.

Working with my Canon EOS 7D, I always expose simultaneous Jps and Camera RAW files. Most of the time the in Camera hi-res Jpg proves acceptable, and simply archive the RAW files for the future.

However, in this instance when I got home, I found that the in-camera Jpg appears to bright to my eye. I re-checked the camera’s histogram for that file and confirmed that the image was exposed correctly.

Histogram.
This is the information displayed at the back of the camera. The histogram is just about ideal. The bulk of the exposure is at the center of the graph and there is virtually no clipping of shadow or highlight areas. (See my earlier post on snow exposure for graph interpretation.)

In previous posts I’ve explained that with modern digital imaging old-school film-based assessments of ‘under’ (too dark) and ‘over’ (too light) exposure do not allow for the most accurate way of selecting exposure. (see: Snow Exposure—Part 1)

Instead of using the image at the back of the camera, or even the photo on my home computer screen, to judge exposure, I use the histogram. This graph allows me to select an exposure that maximizes the amount of information captured by the camera on-site.

In this case, although the Camera processed Jpeg seemed too bright (over exposed), the camera RAW file was perfect.  Since the problem was in the camera’s translation of the RAW to Jpeg, the solution was simple:

I converted the RAW to a Jpeg manually, which produced a result that matched the scene. This retained excellent highlight detail in the snow, produced a pleasing exposure for the side of the locomotive and hills beyond, while retaining good shadow detail in the tree at the left.

Here's the camera RAW file. This has not been interpreted by in-camera processing to conform to a pre-established 'picture style'. The result is perfectly exposed. I simply converted the file to a Jpg manually and scaled it for display here. I did not adjust exposure, contrast, or color. In other words its was an easy fix: there was never really a problem with the file, on with my perception of how the 'landscape' style Jpg had interpreted the image.
Here’s the camera RAW file. This has not been interpreted by in-camera processing to conform to a pre-established ‘picture style’. The result is perfectly exposed. I simply converted the file to a Jpg manually and scaled it for display here. I did not adjust exposure, contrast, or color. In other words it was an easy fix: there was never really a problem with the file, only with my perception of how the ‘landscape’ style Jpg had interpreted the image.

I did not manipulate or adjust the file except to scale the image and convert it to a Jpg for presentation. (the RAW file is far too large to up-load effectively).

For more on snow exposure see:

Photo Tips: Snow Exposure—Part 1

Photo Tips: Snow Exposure–Part 2 Histograms

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2 thoughts on “Daily Post: Snow Exposure Quandry”

  1. You’ve made me a believer in the histogram–and learning to think with the tools and concepts of digital photography from the outset when making a picture.

    Brian, you are very generous in sharing your craft. I enjoy the “how I did it” along with the great pictures.

    Tom Warger

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