GIMP has a desaturate option. Basically it changes your color picture to a grayscale one. When you desaturate an image, you get a prompt saying, “Choose shade of grey based on:” with three options, “Lightness”, “Luminosity”, and “Average”
I’ve always wondered what the difference was, so I tried all three on the same picture to compare. (It’s a snapshot of my car pulling into work!)
Can you tell a difference? I sure can’t.
The reason I thought of doing this test is because I’ve always had this crazy idea to build a 1:1 replica of an Abrams tank, and use it at airsoft games. It would be fitted with a nerf cannon and a high rate of fire coaxial machine gun. Naturally, It needs FLIR, but that stuff’s expensive. I want to simulate FLIR using inexpensive surveillance cameras (no IR filters!), and to do so I would need to remove all the color from the video feed, pump up the contrast, and who knows what else. This test was inconclusive, more experimenting is required!