PyQtGraph - Getting Opaque Area in Scatter Plot Graph

PyQtGraph - Getting Opaque Area in Scatter Plot Graph

Calculating the area of a scatter plot where markers overlap, this task can be a bit complex because pyqtgraph doesn't have a built-in function specifically for this purpose. However, we can approximate this task.

One way to achieve this is to:

  1. Render the scatter plot to an image.
  2. Analyze the image to determine the opaque area.

Here's a step-by-step method:

  1. Create a scatter plot in pyqtgraph.
  2. Render this scatter plot to a QImage.
  3. Count the opaque pixels in the QImage.

Here's an example to demonstrate:

import sys import numpy as np import pyqtgraph as pg from PyQt5.QtWidgets import QApplication app = QApplication(sys.argv) # Create a blank plot with a white background plot = pg.plot() plot.setBackground('w') scatter = pg.ScatterPlotItem(size=10, pen=pg.mkPen(None), brush=pg.mkBrush(255, 255, 255, 120)) plot.addItem(scatter) # Generate some random data points num_points = 1000 data = np.random.rand(num_points, 2) # Set scatter data scatter.setData(pos=data) # Render the scatter plot to a QImage img = plot.renderToArray(None, QtGui.QImage.Format_ARGB32) img = QtGui.QImage(img.data, img.shape[1], img.shape[0], img.strides[0], QtGui.QImage.Format_ARGB32) # Count the opaque pixels opaque_count = 0 for x in range(img.width()): for y in range(img.height()): pixel = img.pixelColor(x, y) if pixel.alpha() > 200: # Adjust the value for the definition of "opaque" opaque_count += 1 print("Opaque pixels count:", opaque_count) if not QApplication.instance(): app.exec_()

Note: This approach counts the number of "nearly" opaque pixels. It's a crude way to estimate the opaque area, especially with small marker sizes or a large number of points, but it gives an idea. You can adjust the alpha threshold value (in this example, set at 200) to fit your definition of "opaque".

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