Thanks, that looks promising. Now to see if I can get the thing to compile, with all of its dependencies...
Thanks again, -- Raul On Mon, Apr 29, 2019 at 10:10 PM Ben Gorte <[email protected]> wrote: > > Hi Raul, > > I would use Lowe's SIFT (Scale Invariant Feature Transform) for that, see > Wikipedia. I just tried it on an "arbitrary" image: selected a part of it > and scaled that down by 0.4321 using bilinear interpolation. Then used SIFT > to extract key points from the original and the scaled-down selection and > 'match' (a little program that comes with SIFT) those: perfect! > > The only issue might be the 'not too slow'; SIFTing my 900 x 600 image > takes almost 2s on an i6 laptop. > > If you want you can mail me one of your image pairs and I will try. > > Greetings from Sydney, > Ben > > > > > > > > On Tue, Apr 30, 2019 at 8:03 AM Raul Miller <[email protected]> wrote: > > > I've got a situation where I've got some large images (maybe on the > > order of 4000 pixels square - though many are not square) which have > > had crops made from them which are quite a bit smaller. 1200 pixels > > wide and 600 high is one fairly common example. > > > > These crops were taken from the original, and with a reduced pixel > > count (that 1200x600 might represent a 3000x1500 pixel rectangle in > > the original image). > > > > Is there a reasonably robust and not-too-slow technique to extract the > > pixel coordinates representing the crop, given the two images? (I > > think in all cases that matter, the size reduction was the same in > > both height direction and width direction. Also, in all cases that > > matter, the crop was reduced in size, not magnified.) > > > > I am also interested in verifying that the coordinates are correct, > > but I expect that that can be done by creating a fresh crop using the > > coordinates and dimensions and comparing that with the original crop. > > > > (I don't think fourier transforms would get me where I need to be. I > > wonder if some sort of wavelet variation might?) > > > > Any clues appreciated... (executable code, if you have it,, would be > > great, but this seems too specialized for that to be a likely > > possibility). > > > > Thanks, > > > > -- > > Raul > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm > > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
