Adding values to new row to a csv file in Python

Question

So what I'm trying to do is iterate over a grayscale image and look at each pixel and write that pixel's grayscale value to the second row (the first row being the pixel number). The following code isn't doing anything so far:

from __future__ import with_statement
from PIL import Image

im = Image.open("my28x28image.png") #relative path to file


pix = im.load()


width, height = im.size
print(width)
print(height)


with open('my28x28image.csv', 'a') as f:
    for y in range(28):
        for x in range(28):
            data.append(pix[x,y])

Answer 1

I wrote you a small utility function which converts a greyscale image stored in a numpy matrix into a csv file.

def greyscale_image_to_csv(img_grayscale, file_name):
    csv_header = ['pixel' + str(i) for i in range(np.prod(img_grayscale.shape))]
    csv_data = [str(j) for i in img_grayscale for j in i]
    csv_string = ','.join(csv_header) + '\n' + ','.join(csv_data) 

    f = open(file_name + '.csv','w')
    f.write(csv_string)
    f.close()

---

Here is an example on how to use this function. I have the following image saved to file which is RGB. I load the image and convert the image to greyscale.

import matplotlib.pyplot as plt
import matplotlib.image as mpimg
import numpy as np

def rgb2gray(rgb):
    r, g, b = rgb[:,:,0], rgb[:,:,1], rgb[:,:,2]
    gray = 0.2989 * r + 0.5870 * g + 0.1140 * b
    return gray

img = mpimg.imread('greyscale_image.png')
img_grayscale = rgb2gray(img)

Finally, we can write a csv using our utility function to get a csv file in the desired format.

greyscale_image_to_csv(img_grayscale, 'test')