Sunday, 5 April 2009

Epson 4990 response testing

Some time ago I tested my Epson 3200 scanner for its ability to plumb the depths of a Stouffer wedge. The reason is to understand (not guess at) how much density the scanner can cope with (meaning how much shadow detail can be recovered from slide scanning).

I scanned the wedge as a linear full range positive and then input the median values obtained from each 'patch'. That's the blue line is the scan value (255 - 0) returned, the red line is the Log10 of that.

Looking at the straight numerical levels shows that it really starts to plateau out at about 17 on the step wedge. It seems like a good result, but when compared to the much older 3200 its not that much different.

Since it is the log difference between the values that is important in film scanning I've placed them in the graph. Interestingly the 3200 actually remains linear in the log responce longer than the 4990.

I don't know if this is a good or a bad thing as film already has non-linear responses in the shoulder of the curve anyway.

Well, anyway it seems that the 4990 goes into the shadows a little better than the 3200, but despite how it seems on scanning film its not screamingly better when measured.

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