pythonimagepython-3.xopencv

Resize an image without distortion OpenCV


I am using python 3 and latest version of openCV. I am trying to resize an image using the resize function provided but after resizing the image is very distorted. Code :

import cv2
file = "/home/tanmay/Desktop/test_image.png"
img = cv2.imread(file , 0)
print(img.shape)
cv2.imshow('img' , img)
k = cv2.waitKey(0)
if k == 27:
    cv2.destroyWindow('img')
resize_img = cv2.resize(img  , (28 , 28))
cv2.imshow('img' , resize_img)
x = cv2.waitKey(0)
if x == 27:
    cv2.destroyWindow('img')

The original image is 480 x 640 (RGB therefore i passed the 0 to get it to grayscale)

Is there any way i could resize it and avoid the distortion using OpenCV or any other library perhaps? I intend to make a handwritten digit recogniser and i have trained my neural network using the MNIST data therefore i need the image to be 28x28.


Solution

  • You may try below. The function will keep the aspect rate of the original image.

    def image_resize(image, width = None, height = None, inter = cv2.INTER_AREA):
        # initialize the dimensions of the image to be resized and
        # grab the image size
        dim = None
        (h, w) = image.shape[:2]
    
        # if both the width and height are None, then return the
        # original image
        if width is None and height is None:
            return image
    
        # check to see if the width is None
        if width is None:
            # calculate the ratio of the height and construct the
            # dimensions
            r = height / float(h)
            dim = (int(w * r), height)
    
        # otherwise, the height is None
        else:
            # calculate the ratio of the width and construct the
            # dimensions
            r = width / float(w)
            dim = (width, int(h * r))
    
        # resize the image
        resized = cv2.resize(image, dim, interpolation = inter)
    
        # return the resized image
        return resized
    

    Here is an example usage.

    image = image_resize(image, height = 800)