# trace_skeleton.py
The python library that calls C APIs directly, wrapped using SWIG.
## Usage
The following functions take in an image representation and return set of polylines (i.e. list of list of tuples).
- `trace_skeleton.from_numpy(arr)` input numpy array
- `trace_skeleton.from_list(arr,w,h)` input flat python list and width and height
- `trace_skeleton.from_list2d(arr)` input python list of list
## Example
```python
import trace_skeleton
import cv2
import random
im = cv2.imread("../test_images/opencv-thinning-src-img.png",0)
_,im = cv2.threshold(im,128,255,cv2.THRESH_BINARY);
polys = trace_skeleton.from_numpy(im);
for l in polys:
c = (200*random.random(),200*random.random(),200*random.random())
for i in range(0,len(l)-1):
cv2.line(im,(l[i][0],l[i][1]),(l[i+1][0],l[i+1][1]),c)
cv2.imshow('',im);cv2.waitKey(0)
```
## Advanced
The aforementioned API's have a tiny linear time overhead for transforming input and output between internal datastructures and python objects. Alternatively, you can use the following:
```python
from trace_skeleton import *
im = "\0\1\0\0\1\0\0\1\0 ..... " #image stored as a (char*)
w = 128 #dimensions
h = 64
trace(im,w,h)
# iterate over each point in each polyline
# by popping them off the internal datastructure
# len_polyline() gets the length of current polyline
# -1 means no more polylines
while (len_polyline() != -1):
n = len_polyline();
for i in range(0,n):
# pop_point() retrieve and remove the next point
# on the polyline. It returns the flat index in image
# mod/div it with width to get (x,y) coordinate
idx = pop_point()
x = idx % w;
y = idx //w;
print(x,y)
print("\n")
```
## Build from Source
Run `compile.sh`. You may need to modify the python include path.
**Developed at
Frank-Ratchye STUDIO for Creative Inquiry at Carnegie Mellon University.**