Monday, 6 August 2007

Metering and highlights in the digital world

Life on Belgrade streets, Serbia, March 2007

Mike Johnston over at T.O.P. was bemoaning the ability of digital to capture highlights for B&W, Kjell H (the lentic blog) had a riposte.

I had a think about this, and I think they are both right. On the one hand we have the ability of digital to capture large amounts of information at the highlight end and, if you know what you're doing with editting software, it is easily recoverable. great, as long as you don't saturate any of the channels. There is then that saturation problem - once it's gone, it's gone: there is no roll-off at the high end as with film. Well known, well understood.

There are times, however, when even careful expose to the right will blow the highlights and the detail is gone. there is also the problem of how your camera meters runs the histogram (for my discussion on EOS histograms look here). Specular highlights, or any small area at the high end is typically lost without significant under-exposure. Picture at the top is an example - the sky is blown-out and any cloud detail there might have been is gone. For this shot, not a problem, but if your subject had a similar small amount of highlight it would be gone forever.

My ideal solution: a mythical filter that reduces contrast at the highlight end of the luminance scale so all the info is crammed in there. The new EOS 1DIII has something similar, I believe - an in-built highlight recovery tool as part of RAW processing.


  1. The problem with the histograms (both camera and RAW converter) is that you get the histogram after conversion. What I would have loved to see is the histogram of the actual raw data. As it is right now, it is a bit difficult to know whether you have got all channels of your raw data below saturation or if the raw converter is doing some magic to recover the highlight from one or two of the channels. But if you actually manage to get the exposure right, the highlight detail from a digital exposure is exceptional.

  2. I agree on RAW histograms.
    However, since I did my testing of histograms (see "The Great EOS metering test" in May archives) I have switched to the high contrast option which has greatly increased my success on expose to right.

  3. Yes, I read that article you wrote a couple of months ago, and I started to experiment as well. The high contrast option sure gives you the right margin. I have shot for a while with the contrast set to low now, and I often ends up using the highlight recovery.

    What really puzzles me is that this information isn't available in the raw converter. Then at least we could have learned more about how the light metering and exposure works on the different cameras.


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