I'm glad this is stimulating discussion. This is the kind of thing I enjoy reading here (especially when somebody can explain things they know.)
Anyway, I'd like to figure out some things about sigmoidal contrast. Is a "sigmoidal contrast" simply an approach to setting the contrast curve we all know from photography and digital imaging? In other words, is it a subset of possible contrast curves that could be uses which follow a sigmoidal shape as described in the formula? >From what I can understand, this means it is a typical contrast curve but: • with the endpoints locked down at blackest black and and whitest white • with a single inflection point somewhere in the middle • and a sigmoidal (s) shape between perfectly straight and infinitely steep (essentially a step function) • presumably this function always has a positive slope and the 's' shape is never inverted into a backward 's' shape. Are my assumptions correct? On Wednesday, December 19, 2012 5:09:02 PM UTC-6, Bruno Postle wrote: > > On Wed 19-Dec-2012 at 12:13 +0100, Frederic Da Vitoria wrote: > > > > But now that I think of it more closely, I understand that > > JohnPW's question is still unanswered and that my answers > > completely missed the point. I expect the faux-bracketing to keep > > the lightest parts of the darkest exposure and the darkest parts > > of the lightest exposure. > > I'm not entirely sure what you are trying to do, but Hugin will > extract 'bracketed' exposures from any photo. By default it uses a > 'sigmoidal' camera response curve to map the data to linear space, > multiply and then map back again - This curve will be quite accurate > if you have calibrated your camera photometric parameters. > > All you have to do is load your photo and increment Eev for the > input or output. > > You can then enfuse these brackets, but this process only really > makes sense if you start with 16bit per channel data created from > RAW. > > -- > Bruno > -- You received this message because you are subscribed to the Google Groups "Hugin and other free panoramic software" group. A list of frequently asked questions is available at: http://wiki.panotools.org/Hugin_FAQ To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/hugin-ptx
