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You are here: Home / The Last Word / Characterizing the Leica M240, part 26

Characterizing the Leica M240, part 26

September 20, 2013 JimK Leave a Comment

As we saw here, modeling the M240 as a normal camera with a slight negative offset helped explain the off noise floor characteristics, but didn’t provide a close match to the way the actual camera performs.

It turns out that negative offsets can model the dark tone errors quite well. Here’s what the green channel of the M240 looks like:

real m240 errors

If you model the camera as having a Gaussian sensor noise floor with a standard deviation of 5.92 electrons and a pre-ADC offset of -4 LSBs (the same values that provided the closest match to the actual camera’s noise floor), and add some gain error as the ISO setting on the camera is changed, you get this:

sim m240 errors

Pretty close!

Here’s the simulation, in case anyone wants to check my work:

sim m240 errors matlab

The mere fact that a model predicts actual behavior doesn’t mean that the real thing works the way the model says it does, but it indicates that’s a possibility.

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