Idaho Airships, Inc.

Several questions (mostly from PAPA Members) have come in over my recent reference to the Contrast Ratio of a 32 bit image.

Keep in mind that an f-stop value (e.g. 2.8, 8) is actually the ratio of the diameter of the lens iris to the focal length of the lens. Because of the reduction in light’s intensity with distance, f 4.5 on a 50mm lens will produce the same exposure as f 4.5 on a 200mm lens even though the iris’ are of different diameters, other things being equal. If you need to, please research “Inverse Square Law.”

An Exposure Value (”EV”) is a linear increment. A 1EV increase in exposure can occur between the f-stops of 1.4 and 2.8, or 8 and 9.5. While the EV scale is linear, increasing or decreasing the diameter of an iris does not produce a regular increase in numeric value, πR² being what it is.

Dynamic Range (a terrible term, if you ask many) is used to refer (photographically) to the range between the lowest and highest exposures at which a transducer produces a suitable signal. A subjective assessment of signal noise is most commonly responsible for establishing the lower limits of the scale.

Most (non-specialty) color films have a DR of about 7 EV, while chromes offer about 5 EV. DSLR’s may capture much more, but analogue to digital (A/D) conversion moderates that range to about 9 EV, though I am noting (it’s anecdotal at this point) perhaps 11 EV with my 1DsMIII and attentive Camera RAW preparations-even at ISO800. Please know that “Recovery,” “Fill Light,” and Noise Reduction may all play a part in producing a suitable signal (image).

Honestly, remapping (HDR Tonemapping, for example) shouldn’t be considered to be producing DR.

Contrast Ratio (”CR”) occurs in a nonlinear scaling. 1 EV is a CR of 2:1, 2 EV is a CR of 4:1, and 9 EV is a CR of 512:1. You simply raise 2 to the power of the EV to calculate the CR. Some might be so bold as to call this an exponential scale!

Thus, when I am working on a 32 bit image with a CR of 692:1, I am working with just over 9 EV. I know the CR because I have software that tells me that sort of thing, and when I have 9 EV while the 32 bit Histogram is still bunched up around the middle…well…I smell the potential for 12-14 EV of DR, or a CR of over 15,000:1. I wouldn’t add Contrast just to see how much I could produce, of course-this is a business. Ahem.

Going to print, even with a 16 bit driver and late model 12-ink printer just brings you back to earth.

Incidentally, a LUX has nothing directly to do with the topic at hand. 1 LUX is equal to 1 lumen per square meter-a measure of illuminance, not luminance. 1 foot-candle is about 12 LUX, and somehow this is all related to the luminance of platinum at its melting point…or perhaps the number of vegisexual albino prairie dogs made paraplegic by hybrid cars driven by Elvis impersonators in Montana during the month of October. The LUX measurement is used in various aspects of Color Management to accommodate human perceptual variabilities when viewing prints or monitors. 1000 LUX is a comfortable illuminance level for a home, but a color managed visual proofing booth or area should be at 1500~2500 LUX. Some sources claim that your monitors should enjoy an ambient LUX of <64! If you hold a print that should be viewed in ~2000 LUX up next to a monitor in <64 LUX conditions…well, you can see the potential problem…

L