Make night vision grainy like map view

[thereaverofdarkness]

I'm still not fully comfortable with night vision, and I was pondering ways to improve it when I noticed that the grainy zoomed-in view on the map looks somewhat like real night vision. I think adding that filter to dark areas when using night vision would be great.

Currently I feel one of the problems with night vision is that it's too easy. It's too easy to just put in night vision goggles and forget that night exists. Then I find myself wondering why everything looks so boring and I realize it's because it's all de-saturated since I never installed lights. I'd prefer if night vision was helpful in letting me see at night without making it so easy I forget that it's night. I want the difference between night and day to be obvious, even if I can still tell what I'm looking at.

The problem with night vision before was that the green filter was obstructive. It was adding green on top of the scene, rather than bringing out the green it already had. It's like the difference between shining a green light on terrain, and shining a regular light but putting a green plastic sheet over it. I think a green filter could look great if it was not an obstructive filter. Both of those test filters in the FFF #168 were even worse because they were way too vivid and distracting to the eye, also that level of contrast is painful to look at. The third one even put green fog halos around light sources.

It's actually easy to solve, but you have to understand the difference between the type of filter you want versus the type that was being used. I don't know the nomenclature for these filters so bear with me as I try to explain:
The filter used originally: renders the scene in full color as if it is fully lit, then adjusts all color values toward a fixed value. This is a destructive filter as it reduces color complexity. Anything darker than the fixed value is lightened but not brightened, for instance if the scene were initially rendered dark, the dark areas would still look dark even though the pixels are technically green rather than black. Even worse, everything that's lighter than the fixed value is made darker.
The filter you want: changes what fraction of the scene is rendered. Without night vision, dark areas render with a lower luminosity. With a properly green night vision filter, dark areas will render with improved luminosity but at cost to their saturation. The current filter is basically doing this, it's simply trading a luminosity scale for a saturation scale, thus lit areas look exactly the same either way. But you could go a step further and make the "dark" areas render still slightly darker, a bit green-biased, and perhaps not completely de-saturated.

The trick to green-biasing is not to add green, but only use the colors already available to do it. That way black is still black and white is still white, only the colors in between are more green than before. There are two ways of doing this:
Method #1.) Trade a percentage of the red and blue for green. For example, something with 120 red, 80 green, 40 blue (a shade of brown) would change to 60 red, 160 green, 20 blue--that's a 50% trade. All leftover amount after green hits 255 is distributed evenly between red and blue. This keeps everything the same luminosity but shifts everything toward green. Pure red or pure blue objects in this render will appear to the human eye as still being red or blue, though the amount of color definition will seem reduced. A filter like this can go well with partial de-saturation, because if things start to look too green it can become uncomfortably bright in appearance.
Method #2.) Render green higher than red or blue. For example if you render only the green part of the image but you render it full, then you get a darker image that's colored green but variances in luminosity are still very apparent. This filter would make green objects look white or lightly colored, while red, violet, or blue objects would look dark or black. You wouldn't want a 100% transformation but a partial filter like this can have a neat effect. For instance, if you render 75% of green and 25% of red and blue, you get 41.67% intrinsic luminosity which appears to our eyes like it's around 2/3rds lit, you have significantly reduced color definition but red and blue objects still have some color visible and are clearly red or blue (unless the viewer has poor color vision). And the de-saturation is already done for you!

Whatever filter you use, making lit areas look the same with or without night vision is probably a good move, but a good night vision filter might make that unimportant.

Throw in that grainy filter from the map view and I think we'd have something that would look really cool, would not be uncomfortable to look at (for most of us), would feel like night vision, would make the night distinct from the day, and yet would still allow you to see just fine. It should come with an optional setting that makes night look exactly like day when using night vision, for anyone with any unique issue with the filter--which also takes care of anyone who can't stand de-saturated night with the current filter. And there should always be support for colorblind people!

I had to get this off my chest. I've had a bunch of experience with mixing colors on computers, so when I saw the night vision filter for the first time back in 0.12, I immediately knew what was wrong and how to fix it. It was a bit frustrating to read FFF #168 and see them struggle to do what I already knew how to do, but I hope I've been able to explain this well enough to make it clear. It's like playing KSP: simple once you get used to it, but entirely un-intuitive until then. Let me know what you guys think!