a bit about Density Range & Scanning

When evaluating a scanner, consideration should also be given to the density range within which the scanner can distinguish variations, and the linearity of the differentiation. Scanners are much like film in that "blocking" can occur at both ends of the density range, with compression especially troublesome in the dense areas of the negative. I am sure it is just a matter of time before scanning a negative, even direct digital capture, will be the method of choice.

A Kodak Uncalibrated Step-Wedge was scanned with a Nikon LS-1000 "slide" scanner. The standard "factory" setting was used. Each density block of the resulting Photoshop image was evaluated with the Histogram function. Since zero density is represented with a value of 255, the "inverted" values were used to plot the blue curve at the right. The red line represents the density of each block of the step-wedge.

Don't try to adjust your monitor - a Photoshop grayscale value of 38 is 85% black, so, even with a properly adjusted monitor, you may isolate the "40" block, but it is unlikely you could distinguish the five values between 24 and 6.

I have as yet been unable to pre-scan manipulate the curve to approach a straight line response.

The argument is frequently given that a photographic negative can store a greater density range than a photographic print. To test the practical implications of this argument, the step-wedge described above was projection printed on Zone VI VC paper using the filtration settings shown. An attempt was made to print the 0.05 density as maximum black while showing an appropriate difference for the 0.35 block. To eliminate development variations, all exposures were made on a single sheet of paper. The silver print was scanned into Photoshop with default settings (Brightness 125, Contrast 125) and is reproduced here. No manipulation other than slight sharpening was done.

The grayscale density values were taken from the Photoshop files of both the print sheet and the negative scan, as described above. The values were inserted into a spreadsheet and the plot function exercised. The result is displayed below.

It is clear that a negative scan produces results which are quite different than those obtained by scanning a silver print, regardless of the grade of paper used.

The "personality" of the images produced by the two methods is quite different!


It is also apparent that, even with very soft paper (in this case 150Y filtration with variable contrast paper) there is little usable density variation above the step-wedge density of 2.15, a point at which negative density increases also are of little value. In fact, if the objective in B&W photography is to produce a negative which prints on number 2 paper, a negative with a density range below 1.55 is desirable (I prefer the vicinity of 1.30). Within this density range, it appears that either a negative OR a print can yield acceptable results.

Since neither the digital printer nor photographic paper respond to linear increases in light with proportional increases in density, producing an expressive print remains an ART rather than a SCIENCE.

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