Looping over pixels in an image

Question

I have the following code which iterates over all pixels of an image and does some manipulations on two images of the same size. I would like to speed it up and to avoid iterating over the positions in a for loop:

import numpy as np import cv2 # Two images of same size image_in = cv2.imread('my_image.png') image_in2 = cv2.imread('my_image2.png') image_new = np.ones(image_in.shape[:2], dtype="uint8") * 255 counter = 0 counter2 = 0 for i in range(image_in.shape[0]): for j in range(image_in.shape[1]): if image_in[i, j] < 255: counter += 1 if image_in2[i, j] == 0: image_new[i, j] = 0 else: image_new[i, j] = 255 counter2 += 1

How can I improve my code?

I simply threshold my image. If the pixel values are greater of smaller then a threshold, the pixel value of a new image should be set to 0 or 1. — snowflake
– snowflake, Commented Apr 23, 2018 at 12:21
Actually not, I could use np.count_nonzero on image_new at the end...Good point! — snowflake
– snowflake, Commented Apr 23, 2018 at 12:31

gbartonowen · Accepted Answer · 2018-04-23 13:35:34Z

I think the trick is trying to vectorise this as much as possible:

By the look of it, the code is trying to threshold at 0 and count pixels under 255.

We can change the first part of the loop to:

counter = np.sum(image_in < 255) # Sums work on binary values counter2 = np.sum(np.bitwise_and(image_in < 255, image_in2 != 0))

And the second to:

# This is 0 or 1 depending on whether it is == 0 image_new[:,:] = (image_in2 != 0) # image_new[i,j] = (image_in2[i,j] != 0) # So scale the values up with a simple multiplcation image_new = image_new*255 # image_new[i,j] = image_new[i,j]*255

But how do I get the value of the second counter, it should count only pixels with values of 255 where the same position of image2 has the value 0. — snowflake
– snowflake, Commented Apr 23, 2018 at 13:02
The rest of the image1 contain pixel with values of 255 but they should be excluded in the count. — snowflake
– snowflake, Commented Apr 23, 2018 at 13:04
Added counter2, this isn't the cleanest way of doing this but it works pretty efficiently — gbartonowen
– gbartonowen, Commented Apr 23, 2018 at 13:06

Stack Exchange Network

Looping over pixels in an image

1 Answer 1

You must log in to answer this question.

Hot Network Questions

Looping over pixels in an image

1 Answer 1

You must log in to answer this question.

Related

Hot Network Questions