Recently I finally figured out how to get ffmpegs edge detection filters like sobel and prewitt to work correctly. If you use them normally, they’ll tend to turn everything green… must be something about the planes it’s operating on in yuv modes? This can be fixed by setting the format to rgb, using sobel, then scaling. The scaling can be to the resolution it already was at, it just seems to be isolate later colorspace transformation back to yuv
Confused? So am I 
, but here’s the filters for this video
-vf eq=contrast=10,hue=s=10,format=rgb24,sobel,crop=w=1440:h=1080,scale=1440x1080,dilation,boxblur,vignette,format=yuv420p