IsoCurveItem is slow for large images

[Dig...@gmx.de]

Hi,

I have an ImageView which resides in a PlotItem (for the grid) and want to draw a number of IsoCurveItems on the ImageItem like in the IsoCurveItem example file. The image is about 1000 x 1000 px. Adding the IsoCurveItems seems to be very slow. I put a 

QApplication.processEvents()

in the loop and can literally watch the curves appear one after another. Is there a way to speed things up for larger number of curves?

Thanks...

Here is some test code:

from pyqtgraph.Qt import QtGui, QtCore, QtWidgets

import numpy as np

import pyqtgraph as pg

app = QtGui.QApplication([])

m = n = 1000

x, y = np.meshgrid(range(m), range(n))

data = (x - m / 2) ** 2 + (y - n / 2) ** 2

win = pg.GraphicsWindow()

vb = win.addViewBox()

img = pg.ImageItem(data)

vb.addItem(img)

for level in np.linspace(data.min(), data.max(), 11)[1:-1]:

    c = pg.IsocurveItem(data=data, level=level, pen=(0, 0, 0))

    c.setParentItem(img)

    QtWidgets.QApplication.processEvents()

if __name__ == '__main__':

    app.exec_()

[Vincent Le Saux]

Hi,

IsoCurveItem is know to be slow (look at the source code). You have two possibilities :
    - write another implementation more efficient (and suggest it on github)
    - use another library for the computation of the isolines. Skimage is a good candidate since the method is written in cython.

I personnaly chose the second solution for my app (do not have the time to write annother method), and it work perfectly. I have observed a nice speed-up (x10 to x100) compared to the implementation of pyqtgraph.

Regards,

Vincent

[Dig...@gmx.de]

Thanks for the skimage hint! I'll try it out...