Dynamic Range Explained

I had recently been challenged by shooting some high-contrast scenes with my digital camera (with mixed results) and this prompted me to research the subject of Dynamic Range as it relates to both film and digital imaging generally. I also have a flatbed scanner and a film scanner, so the subject has been lurking in the back of my mind for some time.

It took me quite a while to dig up this information from many sources and to draw some conclusions about the relationships of terms, so for future reference I compiled my findings into a one-page document (see below).

I look forward to reading your ‘Insider’ article on this subject if you get around to it. I also noted with interest on pages 52-53 of the June/July edition some techniques for dealing with high-contrast scenes.

I have copies of your two Pocket Guides, Digital Photography and Printing Digital Photos, and consider them to be superior to many of the other books I have read on the subject. As such, I have recommended them to other budding digital photographers… Congratulations!

John Adlam, via email

Thanks for the feedback and for sending the findings of your research into Dynamic Range, which looks very useful so we’ve posted it below. We’ve scheduled this topic for Insider in Photo Review Oct/Nov 2003, covering both cameras and scanners.
– Margaret Brown.

Dynamic Range of Imaging Media and Processes

Compiled by John Adlam

In photography, dynamic range is the difference between the lowest and highest levels of illumination or brightness with perceptible image detail that can be recorded or displayed by a particular device. Other related and semi-related terms are:
– density range (D = Dmax – Dmin)
– exposure latitude (f-stops)
– colour depth (bits)
– contrast (a function of the slope of the characteristic gamma curve)
– signal-to-noise ratio (decibels)

Ref: A few scanning tips, Chapter 19…by Wayne Fulton (www.scantips.com)

Relationship of terms

Dynamic/Density Range (D) = log10 Intensity Range (Lux)
Dynamic/Density Range (D) = Colour Depth (bits) x 0.3 (where 0.3 is log10 2)
Dynamic/Density Range (D) = Exposure Latitude (f-stops) x 0.3
Therefore, Colour Depth (bits) = Exposure Latitude (f-stops)

NOTE: These relationships apply only at a single point in the process. The practicality of realising these values in actual devices, and between source and output (eg. between capture and display), depends upon factors such as background noise and device transfer characteristics (the slope and shape of the characteristic curve), each of which can yield a disparate result. For example, film positives (slides) capture limited exposure latitude but display a wide density range (high contrast).

Typical values

The following is a comparison-guide of typical (average) values quoted in various books and articles. Some variation exists between articles, which may be due to:
– interpretation of how much of the dynamic range is actually useful in maintaining image detail at the extremes of highlight and shadow (due to the flattening-off of the characteristic curve, or the influence of noise)
– improvements in technology over time (depends when the article was written).