algorithm to draw image selection

Question

I have an image with size of M*N. Each pixel can be selected or not selected.

Given selection values for each pixel (selected or not), what is the most efficient algorithm to get the set of polygons which represents a selection?

If your example the selection mask contains only connected lines that are already polygons. What exactly is the question? — MrSmith42
– MrSmith42, Commented Apr 9, 2021 at 12:55
Edited the question. The selection mask contains selection value for each pixel, not lines or polygons. — razor3x
– razor3x, Commented Apr 9, 2021 at 13:01
@razor3x "Given selection values for each pixel (selected or not)" you mean that you will provide MxN Binary Array with 1, 0 values 1 selected, 0 Non selected? or just the corner points, or the bordering Lines? — Bilal
– Bilal, Commented Apr 9, 2021 at 14:58
@Bilal It is MxN binary array with 1, 0 values for each pixel — razor3x
– razor3x, Commented Apr 9, 2021 at 17:31
@razor3x you need two simple steps: 1. cv2.findContours to find contours, 2. cv2.approxPolyDP to approximate them into polygons, see this tutorial for more details. — Bilal
– Bilal, Commented Apr 10, 2021 at 4:09

MrSmith42 · Accepted Answer · 2021-04-09 13:12:54Z

1

Diagonals might be tricky, because of pixel-exact rounding errors, so I would go only for rectangles with horizontal and vertical lines (overlapping ones can be merges to a polygon)

I would perform the following steps:

connect selected neighbours of selected pixels to horizontal lines
connect horizontal lines to rectangles
connect overlapping/touching rectangles to a polygon

answered Apr 9, 2021 at 13:12

MrSmith42

10.2k6 gold badges41 silver badges52 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Jean-Baptiste Yunès · Accepted Answer · 2021-04-09 15:47:05Z

1

I think any filling algorithm can be suitable:

get a selected pixel not already used
start from it and fill the surface defined by all its connected pixels
this will define a polygon (just retain horizontal/vertical extremas)
restart with any selected pixel already not considered to get another polygon

answered Apr 9, 2021 at 15:47

Jean-Baptiste Yunès

36.6k4 gold badges51 silver badges76 bronze badges

Collectives™ on Stack Overflow

algorithm to draw image selection

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related