The USAF 1951 Resolution Test Chart on PhotoCD

This page is dual purpose; to explain the USAF 1951 test chart, and to establish the real-world resolution of Kodak Photo-CD.

The Chart

I submitted a copy of the chart, mounted in a standard plastic slide mount, to my local photo lab for conversion to photocd. The original chart resolves 160 line pairs per millimeter. The entire chart consists of as many copies of this test target as will fit on the film. Each target has five groups of six elements,each with five pairs of horizontal and five pairs of vertical lines. The actual size of the line pairs doubles with every seventh element. To determine resolution, simply identify the smallest element in which you can clearly distinguish all the line pairs, and read the corresponding resolution from the chart at the right.

Here is a snippet from a test group in the center.
Element  Group 0 Group 1 Group 2 Group 3 Group 4
Element 1 10.0 lppm 22.0 lppm 40.0 lppm 80.0 lppm 160 lppm
Element 2 11.2 lppm 22.4 lppm 44.9 lppm 89.8 lppm n/a
Element 3 12.6 lppm 25.2 lppm 50.4 lppm 101 lppm n/a
Element 4 14.1 lppm 28.3 lppm 56.6 lppm 113 lppm n/a
Element 5 15.9 lppm 31.7 lppm 63.5 lppm 127 lppm n/a
Element 6 17.8 lppm 35.6 lppm 71.3 lppm 143 lppm n/a
The Chart, verses theoretical PhotoCD resolution

Standard photocd's highest resolution scan is 3072x2048 pixels. Theoretically, this ought to be able to represent on the order of 42 line pairs/mm. As I read this scan, group 2 element 1 is clearly resolved. Group 2 element 3 is not clearly resolved, but still distinguishable from a uniform gray, and in a pinch you might be able to count the lines reliably. Referring to the chart, this corresponds to a resolution of between 40 and 50 line pairs per millimeter. So, at least by this lab on this day, the scan captured as much resolution from the film as it could reasonably be expected to do. Good!

A few other notes

This copy of the test target was taken from the center of the scanned image. Resolition was just a good at the edge. Also Good!.

The colorimitry of this image is a little bit off; the actual chart is clear, with black marks. This looks decidedly yellowish, and black isn't really black. Not so good.

 I got my USAF 1951 test chart a few years ago, for about $20, from the following address.
                Four Designs Co.
                6531 Gross Ave.
                Canoga Park, Ca. 91307
The chart they sell is on a 2x2 hard clear plastic chip, which is filled with copies of the test pattern.

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