is it possible to adjust convex hull to draw blue line instead of green line?

[MRAB]

On 2016-09-17 01:20, meInvent bbird wrote:
> i succeed to use code to draw green line, but green line not draw the
> large area, expect second uploaded picture, the blue line connect
> the bottom of red line graph
>
[snip]

Here's the code with the commented code and print statements removed and 
the indentation fixed:


im = img.copy()

for cnt in contours:
     hull = cv2.convexHull(cnt, returnPoints=True)
     previousx = 0
     previousy = 0

     for c in hull:
         if previousx != 0 and previousy != 0 and c[0][0] != 0 and 
c[0][1] != 0 and abs(previousy - c[0][1]) > 10 and abs(c[0][0] - 
previousx) > 1:
             cv2.line(im, (previousx, previousy), (c[0][0], c[0][1]), 
(0, 255, 0), 2)

         previousx = c[0][0]
         previousy = c[0][1]

>
> https://drive.google.com/file/d/0Bxs_ao6uuBDUWVBFZzVIVGotRlk/view?usp=sharing
>
> expected is
>
> https://drive.google.com/file/d/0Bxs_ao6uuBDUNGZFS2F3WnJERzA/view?usp=sharing
>
I think the problem might be that you're setting previousx to c[0][0] 
and previousy to c[0][1] even if you don't draw the line (because of the 
indentation), so you get a series of unconnected lines.

I'm not sure whether you should be setting previousx and previousy to 0 
each time around the outer loop. I can't test it, but if the previous 
fix doesn't work, it's one more thing to try.