openmv/usr/examples/09-Feature-Detection/find_line_segments.py
Kwabena W. Agyeman a039b5d1c7 Change skip_frames() to use a 2 second timeout.
This was necessary due to the increase in the frame rate. The previous
method did not correlate to time.

All scripts updated.
2017-05-27 19:31:41 -04:00

56 lines
2.5 KiB
Python

# Find Line Segments Example
#
# This example shows off how to find line segments in the image. For each line object
# found in the image a line object is returned which includes the line's rotation.
# Note: Line detection is done by using the Hough Transform:
# http://en.wikipedia.org/wiki/Hough_transform
# Please read about it above for more information on what `theta` and `rho` are.
enable_lens_corr = True # turn on for straighter lines...
import sensor, image, time
sensor.reset()
sensor.set_pixformat(sensor.RGB565) # grayscale is faster
sensor.set_framesize(sensor.QQVGA)
sensor.skip_frames(time = 2000)
clock = time.clock()
# All lines also have `x1()`, `y1()`, `x2()`, and `y2()` methods to get their end-points
# and a `line()` method to get all the above as one 4 value tuple for `draw_line()`.
while(True):
clock.tick()
img = sensor.snapshot()
if enable_lens_corr: img.lens_corr(1.8) # for 2.8mm lens...
# `threshold` controls how many lines in the image are found. Only lines with
# edge difference magnitude sums greater than `threshold` are detected...
# More about `threshold` - each pixel in the image contributes a magnitude value
# to a line. The sum of all contributions is the magintude for that line. Then
# when lines are merged their magnitudes are added togheter. Note that `threshold`
# filters out lines with low magnitudes before merging. To see the magnitude of
# un-merged lines set `theta_margin` and `rho_margin` to 0...
# `theta_margin` and `rho_margin` control merging similar lines. If two lines
# theta and rho value differences are less than the margins then they are merged.
# Setting both the above to zero will greatly increase segment detection at the
# cost of a lot of FPS. This is because when less lines are merged more pixels
# are tested... which takes longer but covers more possibilities...
# `segment_threshold` controls line segment extraction. It's a threshold on the
# magnitude response per pixel under an infinite line. Pixels with a magnitude
# above threshold are added to the line segment.
# `find_line_segments` merges detected lines that are no more than 5 pixels apart
# and no more than 15 degrees different to create nice continous line segments.
for l in img.find_line_segments(threshold = 1000, theta_margin = 15, rho_margin = 15, segment_threshold = 100):
img.draw_line(l.line(), color = (255, 0, 0))
# print(l)
print("FPS %f" % clock.fps())