They are the locations
of bright stars and other nearby objects that get in the way
of the observations
of more distant galaxies and are hence masked out in these
maps as no weak - lensing signal can be measured in these
areas.
The Sunlight display uses local tone
mapping, and the hardware based technology tends to adjust the display by every pixel, where the contrast needs to be changed on whiter
areas, thus retaining the brightness, while actually lightening up the darker parts
of the image to make them visible in
bright surroundings.