How to concatenate 1000 images vertically using for loop in python?

Question

I want to concatenate vertically a lot of images. I used skimage to read images then in each iteration io read image and vconcat concatenate the new image on the old image vertically. The result of my code didn't concatenate the images, just combine the images. Any ideas how to make each image in each iteration concatenate vertically on each other?

I want to concatenate the first image and the second image vertically:

but I got this result:

data = []
if nSpectogram < 3765:
    for k in range(0, 21):
        path = io.imread('E:\\wavelet\\spectrograms\\paz05\\'+'spec_'+isPreictal+'_'+str(nSpectogram+1)+'_'+str(k+1)+'.png')
        im_v_array = np.array(im_v)
        data.append(path)
    res = np.concatenate(data)
    plt.imshow(res, cmap='inferno', aspect='auto', interpolation='nearest')

Can you explain the difference between "concat" and "combine"? Examples will goa long way w.r.t what you are getting and what you want — Vivek Kalyanarangan
– Vivek Kalyanarangan, Commented Sep 11, 2020 at 13:16
@VivekKalyanarangan done. I want to concatenate a lot of images vertically. but i got image like the image i added in the post as a result. I just want to concatenate the images vertically not to combine them. — Edayildiz
– Edayildiz, Commented Sep 11, 2020 at 13:33
So your result is a single image without x and y axes? I tried many ways and cannot reproduce. — Parfait
– Parfait, Commented Sep 11, 2020 at 15:40
@Parfait Exactly.it was a single image without x and y axes. — Edayildiz
– Edayildiz, Commented Sep 11, 2020 at 18:14

Vivek Kalyanarangan · Accepted Answer · 2020-09-11 13:53:19Z

6

Use -

merged_img = []
for i in range(3):
    img = io.imread('https://machinelearningblogs.com/wp-content/uploads/2018/03/849825_XL-830x400.jpg')
    merged_img.append(img)

merge = np.concatenate(merged_img)

plt.imshow(merge)

Just add all the images to a list in the for loop after reading them and pass the list to np.concatenate

edited Sep 11, 2020 at 13:53

answered Sep 11, 2020 at 13:47

Vivek Kalyanarangan

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9 Comments

Edayildiz Over a year ago

it didn't work with me. ``` data=[] if nSpectogram <3765: for k in range (0,21): path=io.imread('E:\\wavelet\\spectrograms\\paz05\\'+'spec_'+isPreictal+''+str(nSpectogram+1)+''+str(k+1)+'.png') im_v_array=np.array(im_v) plt.imshow(im_v,cmap='inferno', aspect='auto', interpolation='nearest') data.append(path) res=np.concatenate(data) ```

Edayildiz Over a year ago

I didn't work with me. I have edited my code in the post with you answer. please take a look on it.

Vivek Kalyanarangan Over a year ago

@nadamedhat you have to imshow() the res object outside the loop. Please copy paste the solution provided as-is and check; post that adjust your code accordingly

Edayildiz Over a year ago

@Vivek Kalyanarangan imshow and res are outside the loop. it didn't concatenate the images.

Edayildiz Over a year ago

@Parfait I mean the images didn't concatenate vertically just sowing the image in a different look

|

Parfait · Accepted Answer · 2020-09-11 22:24:59Z

2

Instead of skimage.io (which may be due to a version or CPU issue), consider using matplotlib.pyplot.imread with list comprehension or map. Below demonstrates with OP's two images.

import numpy as np
import matplotlib.pyplot as plt

img_paths = ["OP_Image_1.png", "OP_Image_2.png"]

data = [plt.imread(img) for img in img_paths]
# data = list(map(mpimg.imread, img_paths))

res = np.concatenate(data)
plt.imshow(res, cmap='inferno', aspect='auto', interpolation='nearest')

plt.axis('off')
plt.show()

Specifically, for OP's iteration of files:

import os
import numpy as np
import matplotlib.pyplot as plt

...
spec_path = r"E:\wavelet\spectrograms\paz05"                     # RAW STRING FOR BACKSLASHES
spec_file = f"spec_{isPreictal}_{str(nSpectogram+1)}_{{}}.png"   # F STRING FOR INTERPOLATION

if nSpectogram <3765:
   data = [plt.imread(os.path.join(spec_path, spec_file.format(k+1))) for k in range(21)]

   res = np.concatenate(data)
   plt.imshow(res, cmap='inferno', aspect='auto', interpolation='nearest')
   
   plt.axis('off')
   plt.savefig(os.path.join(spec_path, "Output.png"))

edited Sep 11, 2020 at 22:24

answered Sep 11, 2020 at 19:56

Parfait

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3 Comments

Edayildiz Over a year ago

But I have a lot of images not only 2. can i put path inside img_paths to read each image in each iteration?

Parfait Over a year ago

See extended answer for your current setup. Also, avoid printing to screen with plt.show() but save to file: plt.savefig(...). Not sure why you want 1,000 concatenated images which may become a large file and take a while to process.

Parfait Over a year ago

Great to hear and glad to help. Happy coding!

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