add cut.py: split an img given a coordinates file

fixes #3

cut.py

@@ -0,0 +1,76 @@
+from __future__ import print_function
+import os.path
+from collections import namedtuple
+
+import numpy as np
+import cv2
+
+Point = namedtuple('Point', ('x', 'y'))
+
+def show_exit(im):
+    cv2.imshow('test', im)
+    cv2.waitKey()
+    cv2.destroyAllWindows()
+
+
+def split_image(coord_buf, img):
+    data = coord_buf.read()
+    p1 = Point(*map(int, data.split('\n')[0].split('\t')))
+    p2 = Point(*map(int, data.split('\n')[1].split('\t')))
+    height, width, depth = img.shape
+    # note that axes are inverted: x = alpha * y
+    alpha, b, c = get_cut_params(p1, p2, height)
+
+    left_poly = [(0,0), (b, 0), (c, height), (0, height)]
+    right_poly = [(b, 0), (width, 0), (width, height), (c, height)]
+    only_right = blackened(img, left_poly)
+    only_left = blackened(img, right_poly)
+
+    only_left = crop(only_left, 0, max(b, c))
+    only_right = crop(only_right, min(b, c), width)
+    return only_left, only_right
+
+def crop(img, from_, to):
+    '''crop by width'''
+    return img[0:img.shape[0], from_:to]
+
+def get_cut_params(p1, p2, img_height):
+    alpha = float(p1.x-p2.x)/(p1.y-p2.y)
+    b = p1.x - alpha * p1.y
+    c = alpha * img_height + b
+    print(p1, p2)
+    print(alpha, b, c)
+    return (alpha, b, c)
+
+def blackened(im, poly_to_blacken):
+    bg = [0] * 3
+    mask = np.full(im.shape, 255, dtype=np.uint8)
+    roi = np.array([poly_to_blacken],dtype=np.int32)
+    cv2.fillPoly(mask,roi,bg)
+    return cv2.bitwise_and(im, mask)
+
+def get_parser():
+    import argparse
+    p = argparse.ArgumentParser('taglia taglia')
+    p.add_argument('cut_coordinates_filename', type=argparse.FileType('r'))
+    p.add_argument('img_filename')
+    p.add_argument('--outfile')
+    p.add_argument('--show', action='store_true', default=False)
+    return p
+
+if __name__ == '__main__':
+    args = get_parser().parse_args()
+    img = cv2.imread(args.img_filename)
+    left, right = split_image(args.cut_coordinates_filename, img)
+    if args.outfile is not None:
+        l_fname = '%s.L%s' % os.path.splitext(args.outfile)
+        r_fname = '%s.R%s' % os.path.splitext(args.outfile)
+        cv2.imwrite(l_fname, left)
+        cv2.imwrite(r_fname, right)
+    if args.show is True:
+        cv2.imshow('left', left)
+        cv2.imshow('right', right)
+        cv2.waitKey()
+        cv2.destroyAllWindows()
+
+