Image conversion and re-creation gives cryptic result

Question

So I wrote this little code to try to convert RGB imge to Grayscale taken from this accepted answer. The problem, is that it shows a cryptic image with no likeness to original even when I am just re-creating the original. What do you think is the problem and how should we go about solving it? Also then I want to convert it to Grayscale as per the given array b.

Here's my code:

import matplotlib.image as img
import matplotlib.pyplot as plt
from PIL import Image
import numpy as np

a = img.imread('hCeFA.png')

a = a * 255         #Matplotlib gives float values between 0-1

b = a * np.array([0.3, 0.59, 0.11])
b = np.sum(b, axis = 2) / 3           #Grayscale conversion

img1 = Image.fromarray(a, 'RGB')
img1.save('my.png')
img1.show()                     #Gives a cryptic image

plt.imshow(a/255, interpolation='nearest')     #Works fine
plt.show()

What makes you think `b = a * np.array([0.3, 0.59, 0.11])` is grayscale conversion, and why are you doing nothing with `b`? — user2357112, Jul 25 '18 at 16:46
@user2357112 https://www.tutorialspoint.com/dip/grayscale_to_rgb_conversion.htm — DuttaA, Jul 25 '18 at 16:47
That tutorial says to multiply the individual color channel values by those factors and *add the results together* to determine the grayscale value. — user2357112, Jul 25 '18 at 16:50
@user2357112 if the original image shows cryptic values how can grayscale image have any different outcome, i have tried that already and it has given me the same outcome..anyways i updated the question — DuttaA, Jul 25 '18 at 16:51
@user2357112 like i said i am unable to recreate the 'original' image...and so i am asking how to do that and then convert it into grayscale — DuttaA, Jul 25 '18 at 16:53

score 1 · Accepted Answer · answered Jul 25 '18 at 17:05

1

Better Read the image with the 'I'. Like imread('imageName.imgFormat',"I") That will resolve the issue. It will read image in uint8 format, which i think you desire.

answered Jul 25 '18 at 17:05

lifeisshubh

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But i converted to uint8 by multiplying with 255, why doesnt it work? – DuttaA Jul 25 '18 at 17:09
You think you have converted it to uint8 by multiplying. But you didn't. To convert to uint8 you have to change the type of your container also. ``` a = a.astype(np.uint8) ``` – lifeisshubh Jul 25 '18 at 17:16
What do you mean by container...The dtype? – DuttaA Jul 25 '18 at 17:17
``` a = a.astype(np.uint8) ``` – lifeisshubh Jul 25 '18 at 17:19

Image conversion and re-creation gives cryptic result

1 Answers1