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“Mind the Gap” (HDR advice)

February 4, 2011

For the successful post processing of an HDR image, I believe one of the keys is to ensure that all the necessary bracketed exposures have been captured. And to do that, you must review the histograms of the exposures before moving on to the next shot. In particular, you must be sure that there is at least one image with no highlight clipping and one image with no shadow clipping. In histogram terms, that means capturing an image with a gap to the left (no shadow clipping) and capturing an image with a gap to the right (no highlight clipping). See the two histograms below and note the gap between the histogram border and the start/end of brightness distribution data.

Mind the Gap

When I’m in the field, my little motto for reviewing histograms is “Mind the Gap”. For anyone that has ridden the Tube in London’s underground knows, this is a common expression seen and heard everywhere (if refers to the gap between the subway cars and the platform and how to be mindful that the gap varies from station to station). But in this case, it means taking the time to review the histograms and ensuring you have two exposures at each end of the scale that present a gap between the edge of the histogram and the appearance of data.

So when shooting for HDR, don’t just blindly bracket and move one. Check the histogram and ensure you have fames with the left and right gaps. If not, then you have to make some adjustments and capture additional images. “Mind the Gap” and get better HDR results.

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