On 3/8/07, Sven Neumann <sven@xxxxxxxx> wrote:
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.)
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.)
_______________________________________________ Gimp-developer mailing list Gimp-developer@xxxxxxxxxxxxxxxxxxxxxx https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-developer
