Why is ''ValueError: image is readonly'' in PIL

问题

I want to change pixel in a grayscale pgm image. When I compile the following code it shows image is read-only. I can not change the pixel of the image. How can I fix this error?
Here are my codes:

from PIL import Image
img = Image.open('Image.pgm')
pixval= img.load()
columnsize, rowsize = img.size 

img1 = Image.open('Image.pgm')
pix1 = img1.load()
for i in range(rowsize):
    for j in range(columnsize):
        pix1[j,i]=250
img1.save("share1.pgm")

回答1:

In order to change a pixel, use the following API

image.putpixel((j, i), 250)

In particular, your code becomes

from PIL import Image
img = Image.open('Image.pgm')
pixval = img.load()
columnsize, rowsize = img.size 
for i in range(rowsize):
    for j in range(columnsize):
        image.putpixel((j, i), 250)
img1.save("share1.pgm")

回答2:

You appear to want to use "array notation" to access pixels so you may find it more intuitive and faster to convert your image to a numpy array and do your modifications there.

So, if I start with this 320x240 black image:

#!/usr/local/bin/python3
import numpy as np
from PIL import Image

# Load the image from disk
im = Image.open("image.pgm")

# Convert image to numpy array
na = np.array(im)

# Make entire image grey (128)
na[:,:] = 128

# Make pixel 1,1 white (255)
na[1,1] = 255

# Make rows 20-30 white (255)
na[20:30,:] = 255

# Make columns 80-100 black (0)
na[:,80:100] = 0

# Convert numpy array back to image and save
Image.fromarray(na).save("result.png")

You can merge the first two lines to simplify things like this:

# Load the image from disk and make into numpy array
na = np.array(Image.open("image.pgm"))

来源：https://stackoverflow.com/questions/51908968/why-is-valueerror-image-is-readonly-in-pil

标签

python-2.7

ubuntu-16.04

python-imaging-library

pixels