Practical Example of ETTR
or How to get perfect image quality from an APS-C camera using ETTR
As I was reviewing images for my last post, I noticed some noise in the sky around the moon in one of the shots. This particular image was underexposed (-1 EV), but I had bracketed the exposures (+/-1 EV), so there were two other images of the same scene available at 0 and +1 EV. In Lightroom, I simply copied the develop settings to these two other exposures, then lowered the Exposure slider by one or two stops. Because of the brightness of the moon, I expected the +1 exposure to not be usable, but the moon was not overexposed and had no loss of highlight detail. When I zoomed in to examine the sky, there was almost no noise at all in the brighter exposure-ETTR at work!
I also checked some other areas and realized that the noise was quite bad in several parts of the underexposed image, even though it was captured at ISO 100. In particular, the color noise was terrible in the shadows-see the comparison below. (These comparisons show the fully processed exposures at 200% magnification in Lightroom. I have applied standard sharpening with masking. Luminance noise reduction was set to zero; color noise reduction was left at the default amount of 25.)
The next example shows a comparison of the deep shadows in the image. I don’t see a lot of noise (because I have left these areas dark), but the deep shadows are blocky in the underexposed image. The ETTR image shows more detail in these areas.
The one drawback I noticed to using the ETTR exposure was that the underexposed image had much greater detail in the moon, probably because of the movement of the moon in the longer exposure (1/40 sec versus 1/160 sec). I decided to try creating an HDR composite of the three exposures in Lightroom to see if it would preserve the detail in the moon while eliminating the noise and in fact the merged image turned out quite well.
I hope this example demonstrates the practical usefulness of exposing to the right (ETTR) and HDR. For this image, ETTR provided a very noticeable benefit across 90 percent of the image by eliminating luminance noise that affected the sky and ugly color noise in the darker parts of the photo. And although there was absolutely no need for the typical use of HDR to expand the dynamic range, the benefits of combining multiple exposures to reduce noise and enhance details are apparent.
Bonus tip: I discovered that Lightroom’s Enhance Details feature cannot be used on a merged HDR DNG image. But the HDR Merge does work using Enhanced versions of the bracketed exposures. So for the ultimate in Lightroom image quality, you know what to do…