Introduction

If you do not have mathematical formulas or numerical data and only have a graph image, you may want to read the plot coordinates from the image and quantify it.

I tried using Python's matplotlib to achieve this.

What you are doing

Display image
Read the coordinates by clicking in the displayed image
Circle the click point to save the image

That is. By setting the coordinate axes properly, you should be able to quantify the graph data, but I would like to think about that in the future.

program

$ python3 py_img_test.py
/Users/kk/.pyenv/versions/3.5.2/lib/python3.5/site-packages/matplotlib/backend_bases.py:2437: MatplotlibDeprecationWarning: Using default event loop until function specific to this GUI is implemented
  warnings.warn(str, mplDeprecation)

I got the above warning and couldn't get rid of it, so I put the line below to get rid of the warning.

import warnings;warnings.filterwarnings('ignore')

`` `ginput``` is used to get the click coordinates.

Below is a sentence that adjusts the margins of the image and outputs it, which is often forgotten even though it is often used.

plt.savefig('fig_test.png', bbox_inches="tight", pad_inches=0.2)

Full program

`py_img_test.py`


from PIL import Image
import matplotlib.pyplot as plt
import numpy as np
import warnings;warnings.filterwarnings('ignore')

im=Image.open('fig_PSHQ1.png')
im_list=np.asarray(im)
plt.imshow(im_list)

nn=5
a=plt.ginput(n=nn)
for x,y in a:
    print(x,y)
    plt.plot( x,y, 'ro' )

plt.savefig('fig_test.png', bbox_inches="tight", pad_inches=0.2)
plt.show()

Image display example

If you load a separately created graph (file name: fig_PSHQ1.png) and click 5 points on the image, the console output below and the graph showing the click points in red circles will be displayed and saved.

Console output

$ python3 py_img_test.py
205.951612903 1005.9516129
318.85483871 825.306451613
489.822580645 689.822580645
680.14516129 589.822580645
1125.30645161 415.629032258

Output image

Reference site

Display image

http://qiita.com/zaburo/items/5637b424c655b136527a [http://www.mwsoft.jp/programming/computer_vision_with_python/1_2_matplotlib.html] (http://www.mwsoft.jp/programming/computer_vision_with_python/1_2_matplotlib.html)

Get coordinate values

[http://seesaawiki.jp/python-project/d/%BA%C2%C9%B8%C3%CD%BC%E8%C6%C0(ginput)] (http://seesaawiki.jp/python-project/d/%BA%C2%C9%B8%C3%CD%BC%E8%C6%C0(ginput))

Turn off the warning

http://dothiko.hatenablog.com/entry/2014/11/27/001000

Read image coordinates with Python-matplotlib