How to convert python list of points to numpy image array?

Question

I have a python list of points (x/y coordinates):

   [(200, 245), (344, 248), (125, 34), ...]

It represents a contour on a 2d plane. I would like to use some numpy/scipy algorithms for smoothing, interpolation etc. They normally require numpy array as input. For example scipy.ndimage.interpolation.zoom.

What is the simplest way to get the right numpy array from my list of points?

EDIT: I added the word "image" to my question, hope it is clear now, I am really sorry, if it was somehow misleading. Example of what I meant (points to binary image array).

Input:

[(0, 0), (2, 0), (2, 1)]

Output:

[[0, 0, 1],
 [1, 0, 1]]

Rounding the accepted answer here is the working sample:

import numpy as np

coordinates = [(0, 0), (2, 0), (2, 1)]

x, y = [i[0] for i in coordinates], [i[1] for i in coordinates]
max_x, max_y = max(x), max(y)

image = np.zeros((max_y + 1, max_x + 1))

for i in range(len(coordinates)):
    image[max_y - y[i], x[i]] = 1

not much of a start... but really what means represent anyways... — seberg
– seberg, Commented Oct 1, 2012 at 9:55

seberg · Accepted Answer · 2012-10-01 12:09:27Z

10

Ah, better now, so you do have all the points you want to fill... then its very simple:

image = np.zeros((max_x, max_y))
image[coordinates] = 1

You could create an array first, but its not necessary.

answered Oct 1, 2012 at 12:09

seberg

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1 Comment

seberg Over a year ago

@Alex, well you probably had to know that zoom work on images... Btw. forgot to set the datatype (np.zeros((max_x, max_y), dtype=bool)), though if you want to zoom, maybe no point.

Michelle Lynn Gill · Accepted Answer · 2012-10-01 10:53:21Z

0

Building on what Jon Clements and Dunes said, after doing

new_array = numpy.array([(200, 245), (344, 248), (125, 34), ...])

you will get a two-dimensional array where the first column contains the x coordinates and the second column contains the y coordinates. The array can be further split into separate x and y arrays like this:

x_coords = new_array[:,0]
y_coords = new_array[:,1]

answered Oct 1, 2012 at 10:53

Michelle Lynn Gill

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2 Comments

Pierre GM Over a year ago

... or directly as (x_coords, y_coords)=new_array.T where .T is a shortcut to the .transpose() method.

Michelle Lynn Gill Over a year ago

Rigt, Pierre GM. I almost mentioned that since it's my preferred way as it uses fewer commands. I decided what I wrote was maybe simpler from a conceptual standpoint. The more examples the merrier, though.

Dunes · Accepted Answer · 2012-10-01 09:39:13Z

-1

numpy.array(your_list)

numpy has very extensive documentation that you should try reading. You can find it online or by typing help(obj_you_want_help_with) (eg. help(numpy)) on the REPL.

answered Oct 1, 2012 at 9:39

Dunes

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1 Comment

Alex Over a year ago

I am sorry but how can this help me? I said that I need a numpy array that I can use as input for scipy functions and gave an example (zoom).

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