OpenCV Python: HoughLinesP function produces different results when run with different versions of OpenCV

Question

I have some code from a while ago that runs on an old version of OpenCV (cv2 version=$Rev: 4557 $) and I am trying to update it to work on a later version (cv2 version=3.4.2).

The problem I am having is that when given the exact same parameters, the HoughLinesP function does not always produce the exact same output in both versions.

Here is a bit of code I created that demonstrates this occurrence:

import cv2

print('cv2 version=' + cv2.__version__ + '
')
img = cv2.imread('img.png', 0)
lines = cv2.HoughLinesP(img, 1.0, 0.008726646259971648, 5, minLineLength=14, maxLineGap=9)
print(lines)

Here is the image being used:

Here is the output of each version of the code:

cv2 version=$Rev: 4557 $

[[[371   0 377 127]
  [370   0 376 127]
  [381 193 386 397]
  [383 237 383 255]
  [386 311 387 397]
  [380 194 381 278]
  [383 322 383 294]
  [379 195 379 217]
  [370   4 371  43]
  [385 379 385 395]
  [385 332 385 301]
  [374  34 375  55]
  [381 250 382 207]
  [386 364 387 335]
  [382 279 382 256]
  [372  67 376  90]]]

cv2 version=3.4.2

[[[371   0 377 127]]
 [[370   0 376 127]]
 [[381 193 386 397]]
 [[383 237 383 255]]
 [[386 311 387 397]]
 [[380 194 381 278]]
 [[383 322 383 294]]
 [[379 195 379 217]]
 [[370   4 371  43]]
 [[385 379 385 395]]
 [[385 332 385 301]]
 [[374  34 375  55]]
 [[381 250 382 207]]
 [[386 364 387 335]]
 [[382 279 382 256]]]

When run with OpenCV version 3.4.2, all the same lines as the older version are found except for the last line [372 67 376 90].

Note: The HoughLinesP function also produces results in a different format, in the $Rev: 4557 $ version, the output is a single-item array, that item being an array of all the detected lines.

e.g. [[[line1],[line2],[line3],[line4]]]

Whereas on the 3.4.2 version the output is a multi-item array, where each item is a single item array containing a differnt detected line.

e.g. [[[line1]],[[line2]],[[line3]],[[line4]]]

I am aware of this difference in formats between both versions and have accounted for it in my updated code. What I need to know is why are some of the lines that were detected when using $Rev: 4557 $ not detected when using OpenCV version 3.4.2 and how can I replicate the same results on version 3.4.2.

question from:https://stackoverflow.com/questions/65626203/opencv-python-houghlinesp-function-produces-different-results-when-run-with-dif

Answer 1

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