ASTAP viewer grid

[Kalev Pank]

Why is there a "grid" overlaid in the viewer when viewing a subframe, but not when viewing a stacked file. It changes when zooming. See attached.

[han.k]

The grid in your screenshot is caused by the different in values of the red, green and blue sensitive pixels of a single frame. The pixels are organised in a Bayer pattern. something like:
rg
gb
In the stacked image these pixels are processed such that each four pixels are converted into a luminance and colour signal instead of four individual pixels. See:

https://en.wikipedia.org/wiki/Bayer_filter

cs, Han