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preserving DNG brightness on conversion to RGB

I'm trying to use libRAW to convert some DNG files into a format readable from Matlab.

I take a number of images with specific exposure times and I need the conversion from DNG to any RGB format to preserve the relative luminosity of the images.

If I do the conversion using the Adobe DNG SDK it works well (I use stage 3 of the conversion, before auto-exposure and other processing).

If I use DCraw_emu from the libRAW Windows binaries, I see that the relative brightness of the images is altered.

I attach a plot of the average pixel value for both the cases. You can see that the SDK gives me a linear average value VS exposure time, as I expect, while libRAW does something to the images. I don't mind if the converted images have a gamma/black level applied to them, but nothing else, and they need to sit on a smooth curve.

For libRAW I run

dcraw_emu -W INPUT

Any suggestions?


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