Matplotlib RectangleSelector

rectangle_selector_example.py

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.widgets import RectangleSelector


def _select_rectangle_callback(eclick, erelease):
    """eclick and erelease are the press and release events"""
    x1, y1 = eclick.xdata, eclick.ydata
    x2, y2 = erelease.xdata, erelease.ydata


def toggle_selector(event):
    """Matplotlib interactive selection."""
    if event.key in ['Q', 'q'] and toggle_selector.RS.active:
        toggle_selector.RS.set_active(False)
    if event.key in ['A', 'a'] and not toggle_selector.RS.active:
        toggle_selector.RS.set_active(True)


def select_rectangle(image):
    """Return location of interactive user click on image.

    Parameters
    ----------
    image : AdornedImage or 2D numpy array.

    Returns
    -------
    center, extents
          Rectangle center and extents.
          Coordinates are in x, y format & real space units.
          (Units are the same as the matplotlib figure axes.)
          Rectangle extents are given as: (xmin, xmax, ymin, ymax).
    """
    fig, ax = quick_plot(image)
    # Here are the docs fir the matplotlib RectangleSelector
    # https://matplotlib.org/3.1.0/api/widgets_api.html#matplotlib.widgets.RectangleSelector
    toggle_selector.RS = RectangleSelector(ax, _select_rectangle_callback,
                                           drawtype='box', useblit=True,
                                           # don't use middle button
                                           button=[1, 3],
                                           minspanx=5, minspany=5,
                                           spancoords='pixels',
                                           interactive=True)
    plt.show()
    center = toggle_selector.RS.center  # xy coord, units same as plot axes
    extents = toggle_selector.RS.extents  # Return (xmin, xmax, ymin, ymax)
    return center, extents


def quick_plot(image):
    """Display image with matplotlib.pyplot

    Parameters
    ----------
    image : Adorned image or numpy array
        Input image.

    Returns
    -------
    fig, ax
        Matplotlib figure and axis objects.
    """
    fig, ax = plt.subplots(1)
    display_image = image.data
    height, width = display_image.shape
    try:
        pixelsize_x = image.metadata.binary_result.pixel_size.x
        pixelsize_y = image.metadata.binary_result.pixel_size.y
    except AttributeError:
        extent_kwargs = [-(width / 2), +(width / 2),
                         -(height / 2), +(height / 2)]
        ax.set_xlabel('Distance from origin (pixels)')
    else:
        extent_kwargs = [-(width / 2) * pixelsize_x,
                         +(width / 2) * pixelsize_x,
                         -(height / 2) * pixelsize_y,
                         +(height / 2) * pixelsize_y]
        ax.set_xlabel('Distance from origin (meters) \n'
                      '1 pixel = {} meters'.format(pixelsize_x))
    ax.set_xlim(extent_kwargs[0], extent_kwargs[1])
    ax.set_ylim(extent_kwargs[2], extent_kwargs[3])
    ax.imshow(display_image, cmap='gray', extent=extent_kwargs)
    return fig, ax


def main():
    import fibsem
    rect_coords = select_rectangle(fibsem.data.embryo_adorned())
    print(rect_coords)


if __name__ == '__main__':
    main()