When reading an image for RGB pixel values there is a different green value in matlab and python

Question

When reading an image for RGB pixel values there is a different green value in matlab and python

I want to get pixel values for RGB from image. I did it in Matlab and Python, but I got different values, especially on the green value. I would be grateful if you have any advice on this matter. thanks Here is my code in python

from PIL import Image
import numpy as np

im = Image.open("lena.jpg")
imPixelVal = np.ones(np.size(im))
imSize = np.size(im)

for i in range (0,imSize[0]):
            for j in range (0,imSize[1]):         
                ij = i , j
                p = im.getpixel(ij)
                imPixelVal[i,j] = (0.2989 * p[0]) + (0.5870 * p[1]) + (0.1140 * p[2])
                print p[0]
                print p[1] 
                print p[2]

Also this is the code in Matlab:

Im=imread('lena.jpg');
Img = (ones(size(Im,1),size(Im,2))); 

for i=1:size(Im,1)
      for j=1:size(Im,2)
          Img(i,j)=0.2989*Im(i,j,1)+0.5870*Im(i,j,2)+0.1140*Im(i,j,3);
      end
end
Im(1,1,1)
Im(1,1,2)
Im(1,1,3)

+3

python image-processing matlab rgb getpixel

lisa 22 Aug 14 at 8:41

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1 answer

Schorsch · Answer 1 · 2014-08-22T16:11:42+0000

It looks like images are read in a different "direction" in Python compared to Matlab.
If you change your python code to:

ij = j , i

instead

ij = i , j

you will get the same result as in Matlab.

If you want to Matlab gave the same results as the Python, you'll have to turn i

and j

there:

Img(j,i)=0.2989*Im(j,i,1)+0.5870*Im(j,i,2)+0.1140*Im(j,i,3);

This is how I figured it out through simple debugging:

I first got the image here and saved it as .jpg

.

Then I changed the Matlab loops to

for i=1:2
    for j=1:2

So, I would get the first 4 pixels.

Print to i

, j

and the contents Im

, I got:

i = 1, j = 1
225, 137, 125

i = 1, j = 2
227, 139, 127

i = 2, j = 1
224, 136, 124

i = 2, j = 2
226, 138, 126

Now I have done the same in python:

for i in range (0,2):
    for j in range (0,2):

This gave me:

(0, 0)
225 137 125
(0, 1)
224 136 124
(1, 0)
227 139 127
(1, 1)
226 138 126

This showed me that the order is different from Matlab and Python.
Hence, changing i

and j

in Python from ij = i, j

to ij = j, i

will reproduce the Matlab results.

When reading an image for RGB pixel values ​​there is a different green value in matlab and python

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When reading an image for RGB pixel values there is a different green value in matlab and python