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PyQtGraph – ROI Clicked Signal of Image View
  • Last Updated : 01 Nov, 2020

In this article we will see how we can trigger the roi clicked signal of image view object in PyQTGaph. 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 button on image view get clicked.

We can create a image view 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 clicked method

   def roiClicked(self):

       # printing message

       print(“ROI Changed”)

Below is the implementation 


# 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 clicked method
    def roiClicked(self):
        # printing message
        print("ROI Clicked")
class Window(QMainWindow):
    def __init__(self):
        # setting title
        # setting geometry
        self.setGeometry(100, 100, 600, 500)
        # icon
        icon = QIcon("skin.png")
        # setting icon to the window
        # calling method
        # showing all the widgets
        # 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
        # making label do word wrap
        # setting configuration options
        # creating image view 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
        # Creating a grid layout
        layout = QGridLayout()
        # minimum width value of the label
        # setting this layout to the widget
        # 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 widow
# create pyqt5 app
App = QApplication(sys.argv)
# create the instance of our Window
window = Window()
# start the app

Output : 


ROI Clicked
ROI Clicked
ROI Clicked


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