Edge Smoothing
The
Smooth Edge
feature is an artificial method to reduce aliasing
artifacts at the transformed source image edges. Aliasing artifacts may appear
because the transformation algorithms skip a destination pixel if its source
origin is out of the source image ROI. Thus, borders of the transformed source
image can look stepped:
If the
smoothEdge
flag is set, destination pixels that are
closest to the transformed source image edges are mixed with sampled source
pixels by the following formula:
dstRes
=srcSampled
*(1-a
)+dstExist
*a
where
- srcSampledis the intensity of the source pixel after transformation.
- dstExistis the intensity of the destination pixel before transformation.
- ais the weight of the outer pixel; set by the function.
- dstResis the intensity of the resulting destination pixel.
The edge smoothing method is not universal: in some cases it can improve
the image, but in other cases it can be inefficient. For example, edge
smoothing does not increase the quality of images with high contrast borders,
and it is not recommended to apply edge smoothing to such images.
Edge smoothing is a post-processing operation: it is performed after
transformation. When warping a tiled image, artifacts may appear on tile
borders. In this case, edges are not smoothed.