# Finding linear displacement by comparing patterned feature

**URL:** <https://forum.opencv.org/t/finding-linear-displacement-by-comparing-patterned-feature/15953>\
**Category:** Python\
**Created:** [December 23, 2023, 4:07pm UTC](https://forum.opencv.org/t/finding-linear-displacement-by-comparing-patterned-feature/15953 "2023-12-23T16:07:25Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![ak49](https://avatars.discourse-cdn.com/v4/letter/a/dc4da7/32.png) [@ak49](https://forum.opencv.org/u/ak49)\
**Post date:** [December 23, 2023, 4:07pm UTC](https://forum.opencv.org/t/finding-linear-displacement-by-comparing-patterned-feature/15953/1 "2023-12-23T16:07:25Z")

</div>

I am trying to find the linear displacement of a needle by tracking the patterned feature on a needle.

So I have been able to extract the linear patterns out using binary thresholding.

```auto
# Function to process the frame and detect edges
def detect_edges(frame):
    # Convert the frame to grayscale
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    # Apply Gaussian blur to reduce noise
    blurred = cv2.GaussianBlur(gray, (9, 9), 0)

    # Apply thresholding
    _, thresholded = cv2.threshold(blurred, 180, 255, cv2.THRESH_BINARY)

    return thresholded

```

Then, I isolated the patterns in a manually chosen ROI region. I basically took the intensity values along the middle of the ROI that I chose.

```auto
# Function to get the pixel intensity along a vertical line in the middle of the ROI
def get_pixel_intensity(frame, roi, step):
    # Extract the region of interest
    roi_frame = frame[roi[1]:roi[1]+roi[3], roi[0]:roi[0]+roi[2]]

    # Get the middle column of the ROI
    middle_column = roi_frame[:, roi_frame.shape[1] // 2]

    # Reshape the middle column into chunks of size 'step' and calculate mean for each chunk
    mean_intensities = [np.mean(chunk) for chunk in np.array_split(middle_column, len(middle_column) // step)]

    return mean_intensities

```

This allowed me to produce an output like this,

 ![image](https://us1.discourse-cdn.com/flex020/uploads/opencv/original/2X/e/e2553ea685b8ae75383cbfb228eb69c176d2a02d.png)  
Each block here representing the pattern/teeth.

But this is where I am struggling to translate this into a vertical displacement. How could I compare for example 2 frames back to back to determine the displacement?  
There are some issues that are slightly affecting this where the number of striations representing a teeth in one frame may not be the same number in the next frame. Also some parts of a teeth will eventually go out of frame as it moves.  
Should I be trying to find like a midpoint for each teeth to use when comparing with adjacent frames?

---

<div class="post-metadata">

**Author:** ![crackwitz](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/crackwitz/32/14_2.png) [@crackwitz](https://forum.opencv.org/u/crackwitz)\
**Post date:** [December 23, 2023, 5:48pm UTC](https://forum.opencv.org/t/finding-linear-displacement-by-comparing-patterned-feature/15953/2 "2023-12-23T17:48:42Z")

</div>

[crosspost](https://meta.stackoverflow.com/a/266159):

> <https://stackoverflow.com/questions/77701155/determining-linear-displacement-in-pixel-units-using-linear-patterns-video-inpu>