Option to Brighten/Darken Screenshots

I've been using ReShade on The Sims 3 and it looks really good but unfortunately for some reason the screenshots I take are always very dark, in-game the brightness is perfectly normal. I was thinking if it was possible to have an option to alter the brightness of screenshots, or perhaps is there a proper way to fix this?
The first image is the original screenshot, the second was brightened in GIMP to resemble the in-game look and the third is to show that the screenshots are still dark with all effects disabled (Scroll Lock toggle).

I was unsure of whether to post this on troubleshooting or not, forgive me if I'm wrong to post here.

Are you taking the screenshots with ReShade's screenshot feature or with a third party program?

With ReShade's own feature, I always prefer it to take screenshots in games and so far only this game has given me this issue.

Wrong color space (gamma/linear) conversion during saving I asume.

So is there any workaround for this? I've tried taking screenshots with the in-game function but they don't show the ReShade effects, I assume this is because it takes a screenshot of the render buffer before ReShade injects it's shaders? (I may be saying bananas here, I don't know the exacts of how it works)

Update:
It seems the problem only occurs when taking screenshots in full screen mode, when I tried doing it while windowed it saved the colors correctly.
The first screenshot was taken in windowed mode, the second in full screen mode.