Hello again Borate,
I cannot find a mention of gradient in the titles of the 59 VideoPad FAQ files I accessed through this support page. I consulted the online help through my running VideoPad app, which lists 89 effects, but none of them seem to contain the word "gradient". I could not find a full manual for the PC version of Videopad but the Mac user manual makes only three mentions of gradient, and none of them refer (in a way that I can understand) to selectively altering geometric regions within the raster. My attempts to find instructions to use gradients in VideoPad via Google search only provide results that point back to PhotoPad, and those instructions refer to changing colors, not greyscales and do not refer to geometric regions. I would be grateful if you could point me to VideoPad gradient documentation that would assist me in this matter.
Referring to your sample image, it does not appear to me that there is a helpful improvement. Actually I get a better, but still unsatisfactory result by using "auto levels".
I'm thinking that the sort of feature I need would be the inverse of the existing effect called "spotlight". If that could be set up as an inverse effect, it would provide the solution. But I don't see a way to invert the effect. I can get a poor approximiation of the result I want by setting the spotlight to white and the opacity to 0.10 and playing with the radius but the net result is a loss of clarity.