Hi Lucas, The simple answer to your question "what does the Shadows value selector do" is that it remaps tone values upwards in the darker areas of an image, so as to bring out hidden detail in underexposed areas.
The complete answer is that the Shadows transformation increases the exposure of pixels by a variable amount based on their luminant intensity in an adaptive and non-linear way. The Shadows algorithm builds a cubic, Hermite polynomial approximation of the Gamma distribution PMF where both the k and omega parameters are 2, and then uses this curve to boost exposure accordingly. If you look at Wikipedia's illustration of the Gamma distribution PMF here (http://en.wikipedia.org/wiki/File:Gamma_distribution_pdf.svg) the x-axis corresponds to luminant intensity and the y-axis corresponds to the magnitude of the exposure boost. You can create a tone-mapping curve in UFRaw that does pretty much the same thing, but that task is beyond the scope of this mailing list. Take care, Lucas _______________________________________________ Shotwell mailing list [email protected] http://lists.yorba.org/cgi-bin/mailman/listinfo/shotwell
