I am using the standard JME bloom render pass and i have also tested
the version found in this forum by Lex. Both versions exhibit a square like
Are there some values configured wrong (exposure etc.)?
If your display resolution is small and the scale value given in the BloomPass constructor is something big like 8, then the created RT texture will have a low resolution which will cause the odd bilinear filtering artifacts you see in the screenshot. You need to change either the scale value or the display resolution to reduce the artifact.
... the scale value given in the BloomPass constructor is something big like 8 ...
I just copied the code from somewhere and my scale value was 40! :D
Changing it to something like 2 or 4 works right now. Thanks!