Function cannyPreview

Four-connected flood fill using an absolute scalar tolerance. Fast interactive edge preview: parallel gradients plus NMS, without hysteresis propagation. Use canny for a final connected edge map.

raster.parallel_rows.ParallelRowsResult cannyPreview(
  scope const(float)[] src,
  ulong w,
  ulong h,
  float threshold,
  ref ubyte[] edges,
  ulong workers = 0LU,
  ulong chunk = 1LU
) @trusted;