Regulate the size of the scope with the Radius parameter.

The color properties to compute the maximum pixel can be controlled at the HSV Channels panel. Use the Brightness mode, to get the brightest pixels, or the Saturation mode for the most glaring ones. If you have more than one mode enabled, a pixel has to fulfill all criteria to be drawn white.

Increase the Bias value to raise the comparison tolerance, i.e. the number of pixels, which are converted to white, even if they are not the brightest pixel in their scope (compare Image 2 to Image 3).