> > > vf_edgedetect video filter implements Canny algorithm > > (https://en.wikipedia.org/wiki/Canny_edge_detector) > > > > Important part of this algo is the double threshold step: pixels above > > "high" threshold being kept, pixels below "low" threshold dropped, > > pixels in between kept if they are attached to "high" pixels. > > > > This is implemented in the double_threshold() function. However, > > condition to start checking attached pixels, as it is now and as it > > was in FFmpeg since 2012, only allows checking on the boundary, not > > inside the video. It is a very lucky coincidence that those boundary > > pixels are always 0, otherwise following lines would be reading > > outside of the buffer. > > > > As it is now, double_threshold() only implements "high" thresholding. > > As a result, edges are either noisy or fragmented, depending on "high" > > threshold selection; "low" threshold is simply ignored. > > > > Attached one char patch fixes this. > > > > Please review. > > Looks indeed like the condition is wrong. > > I say looks because I did only look and didn't do actual testing. > > I hope you will answer my question anyway: Does your patch completely > fix the problem or is it sacrificing the treatment of the outer most > pixels? >
> Hi Alexander, Outer pixels are already set to 0 (line 333, memset(tmpbuf, 0, inlink->w <https://ffmpeg.org/doxygen/2.7/structAVFilterLink.html#a08e3e25929bb29d5f6ef768343ff7f57> * inlink->h <https://ffmpeg.org/doxygen/2.7/structAVFilterLink.html#a1efd10db9d097b6d27054da46e06e133> );) This is correct, as it is not possible to properly calculate gradient there. Patch fixes handling of inner pixels and changes nothing for outer pixels. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
