Resizing images of different sizes into 28x28 images and convert those into one csv-file

Question

I have two folders full of images (around 2000 files each) of different sizes. I need all of them in 28x28 format. After that I need to convert all of those images of each folder into one csv-file. Any ideas how I could do that? I'm an absolute beginner in python so please be a little bit patient, if i need more time to understand the basics.

I tried a solution I found here : Converting images to csv file in python

Specifically :

import numpy as np
import cv2
import os

IMG_DIR = 'C:/Users/Anwender/Documents/Uni/KI/Trainingsdaten/Train'

for img in os.listdir(IMG_DIR):
        img_array = cv2.imread(os.path.join(IMG_DIR,img), cv2.IMREAD_GRAYSCALE)

        img_array = (img_array.flatten())

        img_array  = img_array.reshape(-1,1).T

        print(img_array)

        with open('train.csv', 'ab') as f:

            np.savetxt(f, img_array, delimiter=",")`

I hoped that changing img_array = img_array.reshape(-1,1).T into img_array = img_array.reshape(-1,28*28).T would give me the described result but instead delivers : "ValueError: cannot reshape array of size 2500 into shape (784)". I understand that there is no common denominator of both numbers so the dividing process without a remainder is not possible.

Prateek Dhanuka · Accepted Answer · 2019-07-08T12:01:16.973

3

Use PIL to resize the image before converting into CSV.

import numpy as np
from PIL import Image
import cv2
import os

IMG_DIR = 'C:/Users/Anwender/Documents/Uni/KI/Trainingsdaten/Train'

for img in os.listdir(IMG_DIR):
    img_array = cv2.imread(os.path.join(IMG_DIR,img), cv2.IMREAD_GRAYSCALE)

    img_pil = Image.fromarray(img_array)
    img_28x28 = np.array(img_pil.resize((28, 28), Image.ANTIALIAS))

    img_array = (img_28x28.flatten())

    img_array  = img_array.reshape(-1,1).T

    print(img_array)

    with open('train.csv', 'ab') as f:

        np.savetxt(f, img_array, delimiter=",")

edited Jul 08 '19 at 12:01

answered Jul 08 '19 at 11:25

Prateek Dhanuka

380
2
22

I think that solves the main problem. Still, I get the following error message : "img_pil = Image.fromarray(img_array) File "C:\Users\Anwender\AppData\Local\Programs\Python\Python36-32\lib\site-packages\PIL\Image.py", line 2547, in fromarray size = shape[1], shape[0] IndexError: tuple index out of range" – mugdi Jul 08 '19 at 11:43
Sorry, my bad. You'll need to resize before you flatten the image. I have edited the code to reflect that. – Prateek Dhanuka Jul 08 '19 at 12:01

Anubhav Singh · Answer 2 · 2019-07-08T13:17:05.227

You can use cv2.resize() to resize each image to 28X28.

Try below code:

for img in os.listdir(IMG_DIR):
        img_array = cv2.imread(os.path.join(IMG_DIR,img), cv2.IMREAD_GRAYSCALE)
        resized_image = cv2.resize(img_array, (28, 28))
        img_flatten = resized_image.reshape(-1)
        #print(img_flatten)
        with open('train1.csv', 'ab') as f:
            np.savetxt(f, img_flatten, delimiter=",")

In data.reshape function , -1 is used as a placeholder for figure out what the given dimension should be. You can also use resized_image.flatten() in place of img_flatten = resized_image.reshape(-1) to flatten the numpy array to one dimension.

In this case, each image will be saved into the csv file as a numpy array of shape (784,). On adding img_flatten.reshape(-1, 1).T to the above code will convert its shape to (1, 784). It's solely up to you how you want to save.

Resizing images of different sizes into 28x28 images and convert those into one csv-file

2 Answers2