Chain code is a lossless compression technique used for representing an object in images. The co-ordinates of any continuous boundary of an object can be represented as a string of numbers where each number represents a particular direction in which the next point on the connected line is present. One point is taken as the reference/starting point and on plotting the points generated from the chain, the original figure can be re-drawn.
This article describes how to generate a 8-neighbourhood chain code of a 2-D straight line. In a rectangular grid, a point can have at most 8 surrounding points as shown below. The next point on the line has to be one of these 8 surrounding points. Each direction is assigned a code. Using this code we can find out which of the surrounding point should be plotted next.
The chain codes could be generated by using conditional statements for each direction but it becomes very tedious to describe for systems having large number of directions(3-D grids can have up to 26 directions). Instead we use a hash function. The difference in X() and Y() co-ordinates of two successive points are calculated and hashed to generate the key for the chain code between the two points.
Chain code list:
The function does not generate the value 4 so a dummy value is stored there.
Input : (2, -3), (-4, 2) Output : Chain code for the straight line from (2, -3) to (-4, 2) is 333433 Input : (-7, -4), (9, 3) Output : Chain code for the straight line from (-7, -4) to (9, 3) is 0101010100101010
Chain code for the straight line from (-9, -3) to (10, 1) is 0010000100010000100
- Convex Hull | Monotone chain algorithm
- Slope of the line parallel to the line with the given slope
- Draw a line in C++ graphics
- PHP | ImagickDraw line() Function
- Find the other end point of a line with given one end and mid
- Slope of perpendicular to line
- PHP | GmagickDraw line() Function
- Reflection of a point about a line in C++
- Issues with using C code in Python | Set 2
- Swig to wrap C Code
- Morse Code Implementation
- Issues with using C code in Python | Set 1
- Code introspection in Python
- Python code to convert SOP to POS
- Multi-Line printing in Python
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to email@example.com. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.