slimCODE

I have a high-DPI laptop I'm using with two lower-DPI monitors. When editing an average image on the laptop, it obviously looks small. Unfortunately, when I move Paint.NET to a second monitor (bigger but smaller resolution), the image is still very small, even though Paint.NET tells me I'm viewing it at 100%. Paint.NET being a raster graphics editor, I would expect it to use the monitor's pixels 1:1 as opposed to being tricked by DPIs. Is there any way to change this? In this state, the app is useless for my set-up.

Is there a way or an existing plugin that would allow me to change the opacity of pixels in an image based on the brightness? Let's take a grayscale image for example. I'd like to apply a tool to either the whole image or the selected area, where the closer to white pixels are, the less their alpha value is. In this case, opacity would decrease with brightness. Thank you.