Difference between numpy 3D array and openCV imread object

Question

This is the code I used to generate CSV file for all images.

"""Generate data.csv from data folder in working directory. """
from cv2 import imread,cvtColor,COLOR_RGB2GRAY,resize
from os import listdir
from numpy import array,savetxt,hstack

data=[]
for c in listdir('data'):
    i = listdir('data').index(c)
    print('Reading',c)
    for sample in listdir('data/'+c):
        path = 'data/' + c + '/' + sample
        img = imread(path)
        #img = cvtColor(img,COLOR_RGB2GRAY)
        img = resize(img,(150,150))
        row = hstack([img.ravel(),i])
        data.append(row)

data = array(data)
savetxt('data.csv',data,delimiter=',',fmt='%i')

i recover this data using

print('Reading data...')
data = genfromtxt('data.csv',delimiter=',')
X = reshape(data[:,:-1],(data.shape[0],150,150,3))
y = data[:,-1]
print('Data: ',X.shape)

when i use imshow function on this data, it shows white box with some random colored pixels, but when i save this with imsave it saves a normal image.

Why it appeared different for imshow?

I imported numpy, opencv and os for these scripts.

data should be uint8

Miki
– Miki

2018-03-10 13:35:20 +00:00
Commented Mar 10, 2018 at 13:35 — Miki
– Miki, Commented Mar 10, 2018 at 13:35
@Miki, will give a try.

Jatin Katyal
– Jatin Katyal

2018-03-12 12:48:18 +00:00
Commented Mar 12, 2018 at 12:48 — Jatin Katyal
– Jatin Katyal, Commented Mar 12, 2018 at 12:48

André · Accepted Answer · 2025-06-16 11:47:27Z

1

Since no one answered it so far, imshow from OpenCV displays numpy arrays of dtype=int and of shape (h,w,3) with values between 0 and 255 or dtype=float and values between 0 and 1 and shape (h,w,3). If image is shown as white and some random pixel it could be because of values in range (0,255) but of dtype=float or anything else.

Like suggested by @Miki, changing dtype to uint should solve the problem too.

edited Jun 16 at 11:47

André

2,03314 silver badges29 bronze badges

answered Jun 2, 2021 at 18:35

Jatin Katyal

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