pyqtgraph image point selection

Question

I'm trying to make a tool for my lab for manual image registration--where the user can select some points on two different images to align them. I made this in matplotlib, but zooming in/out was way too slow (I think because the images we're aligning are pretty high res). Is there a good way to do that in pyqtgraph? I just need to be able to select points on two image plots side by side and display where the point selections were.

Currently I have the images in ImageViews and I tried doing it with imv.scene.sigMouseClicked.connect(mouse_click), but in mouse_click(evt) evt.pos(), evt.scenePos(), and evt.screenPos() all gave coordinates that weren't in the image's coordinates. I also played around with doing the point selection with ROI free handles (since I could get the correct coordinates from those), but it doesn't seem like you could color the handles, which isn't a total deal-breaker I was wondering if there was a better option. Is there a better way to do this?

Edit:

The answer was great, I used it to make this pile of spaghetti: https://github.com/xkstein/ManualAlign

Figured I'd like it in case someone was looking for something similar and didn't want to hassle with coding a new one from scratch.

Answer 1

Your question is unclear about how you want the program to match the points, here I provide a simple solution to allow you (1) Show an image. (2) Add points to the image.

The basic idea is to use a pg.GraphicsLayoutWidget, then add a pg.ImageItem and a pg.ScatterPlotItem, and each mouse click adds a point to the ScatterPlotItem. Code:

import sys
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QApplication, QMainWindow, QWidget, QHBoxLayout
import pyqtgraph as pg
import cv2 

pg.setConfigOption('background', 'w')
pg.setConfigOption('foreground', 'k')

class ImagePlot(pg.GraphicsLayoutWidget):

    def __init__(self):
        super(ImagePlot, self).__init__()
        self.p1 = pg.PlotItem() 
        self.addItem(self.p1)
        self.p1.vb.invertY(True) # Images need inverted Y axis

        # Use ScatterPlotItem to draw points
        self.scatterItem = pg.ScatterPlotItem(
            size=10, 
            pen=pg.mkPen(None), 
            brush=pg.mkBrush(255, 0, 0),
            hoverable=True,
            hoverBrush=pg.mkBrush(0, 255, 255)
        )
        self.scatterItem.setZValue(2) # Ensure scatterPlotItem is always at top
        self.points = [] # Record Points

        self.p1.addItem(self.scatterItem)


    def setImage(self, image_path, size):
        
        self.p1.clear()
        self.p1.addItem(self.scatterItem)
        # pg.ImageItem.__init__ method takes input as an image array
        # I use opencv to load image, you can replace with other packages
        image = cv2.imread(image_path, 1)
        # resize image to some fixed size
        image = cv2.resize(image, size)

        self.image_item = pg.ImageItem(image)
        self.image_item.setOpts(axisOrder='row-major')
        self.p1.addItem(self.image_item)


    def mousePressEvent(self, event):

        point = self.p1.vb.mapSceneToView(event.pos()) # get the point clicked
        # Get pixel position of the mouse click
        x, y = int(point.x()), int(point.y())

        self.points.append([x, y])
        self.scatterItem.setPoints(pos=self.points)
        super().mousePressEvent(event)

    

if __name__ == "__main__":

    QApplication.setAttribute(Qt.AA_EnableHighDpiScaling)
    app = QApplication([])
    win = QMainWindow()

    central_win = QWidget()
    layout = QHBoxLayout()
    central_win.setLayout(layout)
    win.setCentralWidget(central_win)

    image_plot1 = ImagePlot()
    image_plot2 = ImagePlot()
    layout.addWidget(image_plot1)
    layout.addWidget(image_plot2)

    image_plot1.setImage('/home/think/image1.png', (310, 200))
    image_plot2.setImage('/home/think/image2.jpeg', (310, 200))
    # You can access points by accessing image_plot1.points
    win.show()

    if (sys.flags.interactive != 1) or not hasattr(Qt.QtCore, "PYQT_VERSION"):
        QApplication.instance().exec_()

The result looks like: