import numpy as np
import pyqtgraph as pg

rng = np.random.default_rng(0)
data = rng.random(size=(500, 32768), dtype=np.float32)
yval = np.linspace(-1, 1, data.shape[0], endpoint=True)[:, None]
xval = np.linspace(-1, 1, data.shape[1], endpoint=True)
mask = ((yval**2) + xval**2) > 1
data[mask] = np.nan

pg.mkQApp()
win = pg.PlotWidget()
img = pg.ImageItem(data, axisOrder='row-major')
win.addItem(img)
win.show()
pg.exec()