PyQtGraph – ROI Changed Signal of Image View

In this article, we will see how we can trigger the ROI changed signal of image view object in PyQTGraph.The PyQtGraph is a graphics and user interface library for Python that provides functionality commonly required in designing and science applications. Its primary goals are to provide fast, interactive graphics for displaying data (plots, video, etc.). Widget used for display and analysis of image data. Implements many features like displaying 2D and 3D image data. For 3D data, a z-axis slider is displayed allowing the user to select which frame is displayed. Displays histogram of image data with movable region defining the dark/light levels, editable gradient provides a color lookup table, frame slider may also be moved using left/right arrow keys as well as pgup, pgdn, home, and end. This signal is emitted when the ROI of the image view gets changed.

We can create an image view object with the help of command given below: 

# creating a pyqtgraph image view object
imv = pg.ImageView()

In order to trigger this signal we have to alter the image view class, below is the syntax of the class: 

# Image View class
class ImageView(pg.ImageView):

    # constructor which inherit original
    # ImageView
    def __init__(self, *args, **kwargs):
        pg.ImageView.__init__(self, *args, **kwargs)

    # roi changed method
    def roiChanged(self):

        # printing message
        print("ROI Changed")

Below is the implementation:

Python3

# importing Qt widgets
from PyQt5.QtWidgets import *

# importing system
import sys

# importing numpy as np
import numpy as np

# importing pyqtgraph as pg
import pyqtgraph as pg
from PyQt5.QtGui import *
from PyQt5.QtCore import *


# Image View class
class ImageView(pg.ImageView):

    # constructor which inherit original
    # ImageView
    def __init__(self, *args, **kwargs):
        pg.ImageView.__init__(self, *args, **kwargs)

    # roi changed method
    def roiChanged(self):

        # printing message
        print("ROI Changed")


class Window(QMainWindow):

    def __init__(self):
        super().__init__()

        # setting title
        self.setWindowTitle("PyQtGraph")

        # setting geometry
        self.setGeometry(100, 100, 600, 500)

        # icon
        icon = QIcon("skin.png")

        # setting icon to the window
        self.setWindowIcon(icon)

        # calling method
        self.UiComponents()

        # showing all the widgets
        self.show()

        # setting fixed size of window
        self.setFixedSize(QSize(600, 500))

    # method for components
    def UiComponents(self):

        # creating a widget object
        widget = QWidget()

        # creating a label
        label = QLabel("Geeksforgeeks Image View")

        # setting minimum width
        label.setMinimumWidth(130)

        # making label do word wrap
        label.setWordWrap(True)

        # setting configuration options
        pg.setConfigOptions(antialias=True)

        # creating image view  object
        imv = ImageView()

        # Create random 3D data set with noisy signals
        img = pg.gaussianFilter(np.random.normal(
            size=(200, 200)), (5, 5)) * 20 + 100

        # setting new axis to image
        img = img[np.newaxis, :, :]

        # decay data
        decay = np.exp(-np.linspace(0, 0.3, 100))[:, np.newaxis, np.newaxis]

        # random data
        data = np.random.normal(size=(100, 200, 200))
        data += img * decay
        data += 2

        # adding time-varying signal
        sig = np.zeros(data.shape[0])
        sig[30:] += np.exp(-np.linspace(1, 10, 70))
        sig[40:] += np.exp(-np.linspace(1, 10, 60))
        sig[70:] += np.exp(-np.linspace(1, 10, 30))

        sig = sig[:, np.newaxis, np.newaxis] * 3
        data[:, 50:60, 30:40] += sig

        # Displaying the data and assign each frame a time value from 1.0 to 3.0
        imv.setImage(data, xvals=np.linspace(1., 3., data.shape[0]))

        # Set a custom color map
        colors = [
            (0, 0, 0),
            (4, 5, 61),
            (84, 42, 55),
            (15, 87, 60),
            (208, 17, 141),
            (255, 255, 255)
        ]

        # color map
        cmap = pg.ColorMap(pos=np.linspace(0.0, 1.0, 6), color=colors)

        # setting color map to the image view
        imv.setColorMap(cmap)

        # Creating a grid layout
        layout = QGridLayout()

        # minimum width value of the label
        label.setFixedWidth(130)

        # setting this layout to the widget
        widget.setLayout(layout)

        # adding label in the layout
        layout.addWidget(label, 1, 0)

        # plot window goes on right side, spanning 3 rows
        layout.addWidget(imv, 0, 1, 3, 1)

        # setting this widget as central widget of the main window
        self.setCentralWidget(widget)


# create pyqt5 app
App = QApplication(sys.argv)

# create the instance of our Window
window = Window()

# start the app
sys.exit(App.exec())

Output :

ROI Changed
ROI Changed
ROI Changed
ROI Changed
ROI Changed
ROI Changed
ROI Changed
ROI Changed
ROI Changed
ROI Changed
ROI Changed
ROI Changed
ROI Changed
ROI Changed
ROI Changed
ROI Changed
ROI Changed