Saving an array of pixel values into a text file

Question

I have an array of pixel values from a greyscale image. I want to export these values into a text file or CSV. I have been trying to to this using various function including: xlsxwrite, write, CSV but I have so far been unsuccessful in doing this. This is what I am working with:

from PIL import Image
import numpy as np 
import sys

# load the original image
img_file = Image.open("seismic.png") 
img_file.show() 

# get original image parameters...
width, height = img_file.size
format = img_file.format
mode = img_file.mode

# Make image Greyscale
img_grey = img_file.convert('L') 
img_grey.save('result.png')
img_grey.show()

# Save Greyscale values
value = img_grey.load()

Essentially I would like to save 'value' to use elsewhere.

This does not produce errors but I am unsure about how to deal with the data I have generated. — Alexander Peace, Jan 06 '17 at 16:03
do you want convert your image in something like PGM file format? — valepert, Jan 06 '17 at 16:58
No I just want to save the values from the pixels into a file. — Alexander Peace, Jan 06 '17 at 17:03

score 2 · Accepted Answer · edited May 23 '17 at 12:17

Instead of using the .load() method, you could use this (with 'x' as your grey-scale image):

value = np.asarray(x.getdata(),dtype=np.float64).reshape((x.size[1],x.size[0]))

This is from: Converting an RGB image to grayscale and manipulating the pixel data in python

Once you have done this, it is straightforward to save the array on file using numpy.savetxt

numpy.savetxt("img_pixels.csv", value, delimiter=',')

Note: x.load() yields an instance of a Pixel Access class which cannot be manipulated using the csv writers you mentioned. The methods available for extracting and manipulating individual pixels in a Pixel Access class can be found here: http://pillow.readthedocs.io/en/3.1.x/reference/PixelAccess.html

Saving an array of pixel values into a text file

1 Answers1