How to work with photos with a dynamic range bridging 12 f-stops and more

The human eye can perceive approximately 24 f-stops (http://www.cambridgeincolour.com/tutorials/dynamic-range.htm) when considering the pupil opening and closing in relationship to the light coming in. In contrast, the highest dynamic range a digital camera has achieved so far, is 14 f-stops, which is roughly the same as the most sensitive film (Kodak Vision3, a motion picture film). In order to display the high dynamic range (HDR) of a natural scene with bright and dark areas, you will need to create a HDR image that has been made up of multiple photos.

These photos must be shot, each with a specific dynamic range in mind. For example, one take for the dark areas, one for the mid-tones, and one for the brightest areas. Combined these three shots will often span the entire dynamic range of a scene. Equally often you will need more shots to ensure proper detail in every range of light values your camera is capable of.

HDR doesn’t exist in the film world. Film has a preset dynamic range, such as Kodak Portra 160NC/VC having a range of 12 f-stops. Many scanners can’t even scan the entire range of this film, so your scanner software will need to find a way to work around it if it wants to render the film across its entire range of greyscale values.

SilverFast 8 has a feature that does this: Multi-Exposure. Multi-Exposure takes two scans that are processed together afterwards. It first scans for the upper greyscale values range, then for the dark areas (or vice versa). Multi-Exposure won SilverFast an award (European Digital Press Association’s European Digital Press Association’s “Best Colour Management software of the Year” prize in 2008) and was already available on higher-end scanners such as the Epson Perfection V700/V750 Photo/Pro flatbed scanners.

Recently, SilverFast has developed a version of this algorithm for the Canoscan 9000F Mk II specifically as well. You might wonder why Multi-Exposure wasn’t yet available for this Canoscan sooner. Timing for this type of high-end features largely depends on the scanner manufacturer. The Canoscan couldn’t previously scan wide dynamic range film.

But now, with SilverFast 8, the Canoscan’s greyscale value range has jumped from 1379 to a whopping 9950 values! If you have a film negative, a Kodachrome, or a transmissive positive (a slide) with very dark and very bright areas, it pays off to try scanning it with the Canoscan 9000F Mk II and SilverFast 8’s Multi-exposure. You’ll be surprised at the results. In one fell swoop you’ll also see a dramatic noise reduction…

A more in-depth article on scanning for high dynamic range is here.

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