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Scanning For Resolution Today Tweet This   Forward This

2 April 2013

Resolution Target. From the OpticFilm 120.

Today's modest goal is to scan the SilverFast Resolution Target, based on the USAF-1951 standard, on several scanners. We've already scanned the target on the OpticFilm 120 and are working of CanoScan 9000F and Microtek M1 scans.

SilverFast Imaging provides an in-depth explanation of what the chart measures and how to use it. And it also sells the targets.

But the short version is that the chart is a series of horizontal and vertical bars arranged in sets of three designed to test the resolving power of both the horizontal and vertical resolution of a scanner.

They aren't always specified individually but the horizontal resolution is determined by how densely packed the photocells are on the CCD sensor itself while the vertical resolution relies on how finely the stepping motor moves across the image.

Because the layout of the resolution target is known, a visual examination of its scan to find the smallest distinct set of bars can reveal the maximum number of dots per inch the scanner can see. You translate the location of the sharpest set on the target to a table of values to get that number.

Our previous scanner reviews didn't put much stock in this measurement because real-world results are, finally, what matter. And in the real world sharpness is more than resolution. It's also acutance, which is famously manipulated with unsharp masking.

But recently scanners have claimed almost uselessly high resolution figures. So looking at a scan of the target should give a bit more meaning to the output resolution specification.

How much resolution you need is a different topic, of course. We published a chart in our OpticFilm 120 review showing how scanner resolution relates to print sizes. If you're scanning full frame, that may be all you need to know. Higher resolutions are primarily useful for scanning crops of the image.

More later...

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