How to add X and Y axis to imageItem

[Alessandro Tontini]

Could someone give a minimum example about how to add X and Y axis to an ImageItem?

Thank you

[Patrick]

Hi,

This isn't "minimal", but will help with what you need. Essentially, just add the ImageItem to a plot, then use the translate() and scale() to convert pixels into whatever the real axes coordinates are.

#!/usr/bin/env python3

import sys
import time
import numpy as np
from PyQt5 import QtWidgets
from PyQt5.QtCore import pyqtSignal, pyqtSlot
import pyqtgraph as pg
from pyqtgraph.Qt import QtCore, QtGui
from threading import Thread, Event

# Routine to acquire and serve data
# This might be a camera driver, notifying when a new frame is available
# callback is a function to call with new data
# threadkill is an Event to signal program shutdown
def generate_data(callback, threadkill):
    while not threadkill.is_set():
        # Make a pretty pattern
        height, width = 40, 30
        data = np.zeros((height, width))
        data += np.cos(np.arange(0, 10*np.pi, 10*np.pi/height) - 9*time.monotonic())[:,np.newaxis]
        data += np.cos(np.arange(0, 4*np.pi, 4*np.pi/width) + 4*time.monotonic())[np.newaxis,:]
        callback(data)
        time.sleep(0.03)

class ImageDisplay(pg.GraphicsLayoutWidget):

    # Signal to indicate new data acquisition
    # Note: signals need to be defined inside a QObject class/subclass
    data_acquired = pyqtSignal(np.ndarray)

    # Scale and offset parameters for image
    mm_per_pixel = (0.12, 0.34)
    mm_offset = (34.5, 56.7)

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

        self.data = np.zeros((1, 1))

        # Image plot panel
        self.plot = self.addPlot(row=0, col=0)
        self.image = pg.ImageItem(self.data)
        self.plot.addItem(self.image)
        self.plot.setLabels(bottom='Position (mm)', left='Position (mm)')
         # Draw axes and ticks above image/data
        [ self.plot.getAxis(ax).setZValue(10) for ax in self.plot.axes ]

        # Colourmap bar
        self.cbar = pg.HistogramLUTItem(image=self.image)
        self.cbar.gradient.loadPreset('thermal')
        self.addItem(self.cbar, row=0, col=1)

        # Connect the signal
        self.data_acquired.connect(self.update_data)

        # Make and start the background thread to acquire data
        # Pass it the signal.emit as the callback function
        self.threadkill = Event()
        self.thread = Thread(target=generate_data, args=(self.data_acquired.emit, self.threadkill))
        self.thread.start()

    # Kill our data acquisition thread when shutting down
    def closeEvent(self, close_event):
        self.threadkill.set()

    # Slot to receive acquired data and update plot
    @pyqtSlot(np.ndarray)
    def update_data(self, data):
        self.image.setImage(data)
        # Scale/translate image to correct size/position on axes
        self.image.resetTransform()
        self.image.translate(self.mm_offset[0] - self.mm_per_pixel[0]/2, self.mm_offset[1] - self.mm_per_pixel[1]/2)
        self.image.scale(self.mm_per_pixel[0], self.mm_per_pixel[1])

def main():
    app = QtWidgets.QApplication(sys.argv)
    window = ImageDisplay()
    window.show()
    if (sys.flags.interactive != 1) or not hasattr(QtCore, 'PYQT_VERSION'):
        sys.exit(app.exec_())

if __name__ == '__main__':
    main()

Patrick

[Alessandro Tontini]

Hi Patrick,

it worked perfectly. Thank you very much!!