## Issue

Currently, I am working on an OCR project where I need to read the text off of a label (see example images below). I am running into issues with the image skew and I need help fixing the image skew so the text is horizontal and not at an angle. Currently the process I am using attempts to score different angles from a given range (code included below), but this method is inconsistent and sometimes overcorrects an image skew or flat out fails to identify the skew and correct it. Just as a note, before the skew correction I am rotating all of the images by 270 degrees to get the text upright, then I am passing the image through the code below. The image passed through to the function is already a binary image.

Code:

```
def findScore(img, angle):
"""
Generates a score for the binary image recieved dependent on the determined angle.\n
Vars:\n
- array <- numpy array of the label\n
- angle <- predicted angle at which the image is rotated by\n
Returns:\n
- histogram of the image
- score of potential angle
"""
data = inter.rotate(img, angle, reshape = False, order = 0)
hist = np.sum(data, axis = 1)
score = np.sum((hist[1:] - hist[:-1]) ** 2)
return hist, score
def skewCorrect(img):
"""
Takes in a nparray and determines the skew angle of the text, then corrects the skew and returns the corrected image.\n
Vars:\n
- img <- numpy array of the label\n
Returns:\n
- Corrected image as a numpy array\n
"""
#Crops down the skewImg to determine the skew angle
img = cv2.resize(img, (0, 0), fx = 0.75, fy = 0.75)
delta = 1
limit = 45
angles = np.arange(-limit, limit+delta, delta)
scores = []
for angle in angles:
hist, score = findScore(img, angle)
scores.append(score)
bestScore = max(scores)
bestAngle = angles[scores.index(bestScore)]
rotated = inter.rotate(img, bestAngle, reshape = False, order = 0)
print("[INFO] angle: {:.3f}".format(bestAngle))
#cv2.imshow("Original", img)
#cv2.imshow("Rotated", rotated)
#cv2.waitKey(0)
#Return img
return rotated
```

Example images of the label before correction and after

Before correction `->`

After correction

If anyone can help me figure this problem out, it would be of much help.

## Solution

Here’s an implementation of the Projection Profile Method algorithm for skew angle estimation. Various angle points are projected into an accumulator array where the skew angle can be defined as the angle of projection within a search interval that maximizes alignment. The idea is to rotate the image at various angles and generate a histogram of pixels for each iteration. To determine the skew angle, we compare the maximum difference between peaks and using this skew angle, rotate the image to correct the skew.

Original `->`

Corrected

Skew angle: -2

```
import cv2
import numpy as np
from scipy.ndimage import interpolation as inter
def correct_skew(image, delta=1, limit=5):
def determine_score(arr, angle):
data = inter.rotate(arr, angle, reshape=False, order=0)
histogram = np.sum(data, axis=1, dtype=float)
score = np.sum((histogram[1:] - histogram[:-1]) ** 2, dtype=float)
return histogram, score
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
thresh = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY_INV + cv2.THRESH_OTSU)[1]
scores = []
angles = np.arange(-limit, limit + delta, delta)
for angle in angles:
histogram, score = determine_score(thresh, angle)
scores.append(score)
best_angle = angles[scores.index(max(scores))]
(h, w) = image.shape[:2]
center = (w // 2, h // 2)
M = cv2.getRotationMatrix2D(center, best_angle, 1.0)
corrected = cv2.warpAffine(image, M, (w, h), flags=cv2.INTER_CUBIC, \
borderMode=cv2.BORDER_REPLICATE)
return best_angle, corrected
if __name__ == '__main__':
image = cv2.imread('1.png')
angle, corrected = correct_skew(image)
print('Skew angle:', angle)
cv2.imshow('corrected', corrected)
cv2.waitKey()
```

**Note:** You may have to adjust the `delta`

or `limit`

values depending on the image. The `delta`

value controls iteration step, it will iterate up until the `limit`

which controls the maximum angle. This method is straightforward by iteratively checking each angle + `delta`

and currently only works to correct skew in the range of +/- 5 degrees. If you need to correct at a larger angle, adjust the `limit`

value. For another approach to handle skew, take a look at this alternative method.

Answered By – nathancy

Answer Checked By – Katrina (AngularFixing Volunteer)