How to make 2d images with PyPNG with 2D Python Lists

Question

So reading the readme, I expected the following code:

import png
R = 10
G = 255
B = 0
color = [[ (R,G,B), (R,G,B), (R,G,B) ],
         [ (R,G,B), (R,G,B), (R,G,B) ]]

png.from_array(color, 'RGB').save("small_smiley.png")

to output a 2x3 image.

However, I get assertion errors (no description provided).

Is there something I'm doing wrong? Is there a way to convert a 2D python list into an image file that's easier than messing with PyPNG?

Thanks

score 3 · Accepted Answer · edited May 23 '17 at 10:29

3

PyPNG's from_array doesn't support 3 dimensional matrices.

From the source comment for from_array:

The use of the term 3-dimensional is for marketing purposes only. It doesn't actually work. Please bear with us. Meanwhile enjoy the complimentary snacks (on request) and please use a 2-dimensional array.

Instead, consider the Numpy/PIL/OpenCV approaches described here.

Edit: The following code works, using numpy and Pillow:

from PIL import Image  # Pillow
import numpy as np     # numpy

R = 10
G = 255
B = 0
color = [[ (R,G,B), (R,G,B), (R,G,B) ],
         [ (R,G,B), (R,G,B), (R,G,B) ]]

img = Image.fromarray(np.asarray(color, dtype=np.uint8))
img.save('small_smiley.png')

edited May 23 '17 at 10:29

Community

1
1

answered Mar 20 '15 at 10:50

jedwards

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Is there no way to go from using pure python lists to PNG? – dcheng Mar 20 '15 at 10:58
@dcheng there is, there are a list of alternatives on the the other question I linked in my answer. I'll also edit this answer to show you how you could use numpy and pillow to create your PNG file. – jedwards Mar 20 '15 at 11:09

score 1 · Answer 2 · answered Sep 08 '15 at 13:21

1

With PyPNG's recent release your code now works!

answered Sep 08 '15 at 13:21

David Jones

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How to make 2d images with PyPNG with 2D Python Lists

2 Answers2