Trying to manipulate images using Python

Question

I am trying to learn Python, this is the first code that I have written:

    #!/usr/bin/python
    # Filename: read_image.py


    f=open('1.raw','r+b')
    image=f.read()
    f.close()


    f=open('copy.raw','w+b')
    f.write(image)
    f.close()

    for i in range(1,256):
        image[i]=0

In the first part I am simply reading a '.raw' image as a binary file and making a copy of it. This part works fine on its own and I get a copy of the image after execution of the code. However I wish to manipulate this image, for starters I was trying to blacken the first line of the image, however I get the following error:

Traceback (most recent call last):
  File "C:/Python32/read_image.py", line 15, in <module>
    image[i]=0
TypeError: 'bytes' object does not support item assignment

I tried using 'int' type variables by copying the image into them, however the error persists except instead of 'bytes' object does not support assignment, I get 'int' object does not support assignment. How should I go about solving this problem?

Please note this is a grayscale image, and the pixel values range from 0 to 255, I tried printing the array image on the shell and it showed me values in this range.

SirDinosaur · Accepted Answer · 2011-05-11 07:03:22Z

3

If you're really trying to do image processing in Python, try the Python Imaging Library* (PIL) found here: http://www.pythonware.com/products/pil/

[*] Keep in mind that you will have to use Python 2.x as opposed to 3.x if you use this library, unfortunately as is currently the case with a lot of powerful python libraries.

answered May 11, 2011 at 7:03

SirDinosaur

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1 Comment

Kedar Over a year ago

I just wanted to write my first bit of code... But Ill be sure to use the library if I have to implement anything.. read the documentation.. seems very useful.. Thank you!

Zach Kelling · Accepted Answer · 2011-05-11 07:09:37Z

3

In Python bytes are immutable. You can't change them, that's why it gives you an error when you try to do item assignment. You could convert your immutable bytes object into a bytearray:

image = bytearray(image)
for i in range(1,256):
    image[i]=0

edited May 11, 2011 at 7:09

answered May 11, 2011 at 6:58

Zach Kelling

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5 Comments

Kedar Over a year ago

Okay, tried converting it to a bytesarray, get the following error: NameError: name 'bytesarray' is not defined,

Zach Kelling Over a year ago

Sorry, it's bytearray. I did typo that.

Kedar Over a year ago

Thanks a lot! The 'int' object doesnt support assignment too.. should I convert it to an intarray as well.. Coz I may have to manipulate integer arrays as well in the future..

ThomasH Over a year ago

@Kedar No, you just use a normal list and fill it with ints: a = [1,2,3]; a[1]=5

Kedar Over a year ago

Hello Thomas... But how can I create lists without initializing them? Because I want to store all the pixel values in an integer/float array and then manipulate this array and then round off this array and copy the values back into a byte array... Can this be achieved in Python?

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