Gamma encoding

[ian moore]

I recently took a series of photographs of a grey card to test the exposure calibration of my Leica R9. I put the grey card in even light,zoomed in,out of focus,and took a series of exposures.First exposure was at the camera's recoomended settings,then I underexposed by -1 EV,then -2 EV,then -3 EV,then +1 EV,etc.

I had the film developed and the series of tones seemed correct. At -3.5 EV the negative had very slight density,slightly above the film base,as it should be.

Then I scanned the initial first exposure which should represent 18% density ie midtone. When I scanned it,using a Nikon 5000 ED,the histogram showed the three channels near the right edge (approx. 235 for each channel). Based on gamma encoding theory,and the fact that histograms represent gamma encoded digital data,the first exposure should be about 50% brightness ie midtone on the histogram.

I would have expected 128 or so (ignoring noise and grain) for each channel. My monitor is calibrated and profiled,gamma set at 2.2 etc.

Am I missing something?

As usual,thanks for all help.

Ian Moore

[Manfred M]

Ian - I wonder if the your scanner software or firmware is the cause of this issue.

I ran into what I suspect might be related problem some years ago when I scanned some "dark" slides using a Minolta Dimage slide / negative scanner. It "helpfully" corrected the exposure for me.