On Thu, 2013-05-30 at 18:11 +1200, johannes hanika wrote: > the keystone correction formula uses a perspective correction approach > (i.e. image plane x and y shortening is proportional to 1/z in 3d and > different for every pixel, much like > http://en.wikipedia.org/wiki/Texture_mapping#Perspective_correctness). > i don't see why you would need additional constant scaling?
I have to think that out to see if what you say meets my objection. As best I can tell, the exif data contains only the size of the image and the distance at which you are focused. (I think that is the 'z' you refer to) In principle, the program could calculate the correction in height (or width) for a trapezoid filling the image plane when it is transformed into a rectangle by the keystone setting. I can't be sure without thinking about it whether this works for a smaller trapezoid, but I suppose it does also. So the only remaining issue is whether there is any significant change needed because the trapezoid->rectangle transformation may be at a distance different from the distance at which the lens is focused. Because there is considerable depth of field, it could be fairly far off from that. > > > -jo > > > > On Thu, May 30, 2013 at 8:46 AM, Leonard Evens > <[email protected]> wrote: > Sometimes, after correcting either vertical or horizontal > keystoning, > so that the lines I want parallel are parallel, I also want > to change the > vertical or horizontal scaling. That is necessary because > the keystoning > correction alone may not yield the right scale. If one knows > the position of > the lens and the actual dimensions of the building, or if one > knows the > position of the lens and the angle at which the lens axis > points, one can > calculate the proper scaling, but, while the lens position may > be in the > exif info, the other information is not. So one has to > correct the scale > by eyeballing it. > > I can't find a darktable plugin to do it. > > Leonard Evens [email protected] > Professor Emeritus, Department of Mathematics, Northwestern > University > > > > ------------------------------------------------------------------------------ > > > > > ------------------------------------------------------------------------------ > Introducing AppDynamics Lite, a free troubleshooting tool for > Java/.NET > Get 100% visibility into your production application - at no > cost. > Code-level diagnostics for performance bottlenecks with <2% > overhead > Download for free and get started troubleshooting in minutes. > http://p.sf.net/sfu/appdyn_d2d_ap1 > _______________________________________________ > Darktable-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/darktable-users > > -- Leonard Evens [email protected] Professor Emeritus, Department of Mathematics, Northwestern University ------------------------------------------------------------------------------ Introducing AppDynamics Lite, a free troubleshooting tool for Java/.NET Get 100% visibility into your production application - at no cost. Code-level diagnostics for performance bottlenecks with <2% overhead Download for free and get started troubleshooting in minutes. http://p.sf.net/sfu/appdyn_d2d_ap1 _______________________________________________ Darktable-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/darktable-users
