I'm trying to create a pretty simple "starfield" by using noise and then playing with the Levels. When I go to adjust the levels, everything looks good in the preview. However, when I click "ok" the image reverts back to what it looked like before, with maybe a VERY slight change, but nowhere close to what my preview had shown originally. I'm not sure what could be causing this, but it does the same thing whether I try levels, brightness/contrast, and threshhold. Any suggestions on how to fix this?
Zoom in to 100%, then judge the results.
Zoomed out, you're seeing the adjustment applied to downsampled (averaged) pixels.