On Thu, 08 Mar 2007 11:54:25 +0100, David Gowers <00ai99@xxxxxxxxx> wrote: > On 3/8/07, Sven Neumann <sven@xxxxxxxx> wrote: >> >> Hi, >> >> > If you rotate by exactly 90 degrees, this is always done with >> > INTERPOLATION_NONE, no matter what you select in the tool options. >> >> Perhaps this is the culprit? An offset seems unavoidable if the >> transformation is performed without interpolation. So perhaps all we >> need to do is to remove this optimization (which is supposed to speed up >> rotations by multiple of 90 degrees)? > > > BTW, do you think the rotation centre should be snapped to 0.5 pixel > increments when interpolation is NONE? It doesn't make sense to have any > more precision at that point (and can introduce glitches -- for instance, > try floating a rectangular region, then dragging the rotation centre to > the > top left as precisely as you can, setting it to rotate 90 degrees, and > performing the rotation... -- compared to inputting the coordinates of > the > top left yourself and then performing the 90 degree rotation. In the > first > case, even fractional imprecision means the result is not even in the > right > place.) > > Anyway, in the case of a 90 degree rotation, it seems unlikely that the > user > would want it misaligned with the pixels -- in which case no > interpolation > is needed and the result should be exactly right. > > > Simple test case that uniformly fails, currently: > > * Select a rectangular region of the picture. > * Float it > * Rotate it. Set the rotation centre to the exact top left (by first > positioning the centre near it, then editing the coordinates in the > rotation > dialog to make them exact). Set the angle to 90 degrees and the > interpolation to NONE. Supersampling option appears to have no effect in > this case. > * The result may be offset by 1 pixel in X and/or Y axis; It is also > missing > one line of pixels (which line is omitted varies.) I think you can achieve the same results without floating. Just try a rotate. gg _______________________________________________ Gimp-developer mailing list Gimp-developer@xxxxxxxxxxxxxxxxxxxxxx https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-developer
