I learned photography in high school with a Vivitar 220 35mm film camera and numerous rolls of black and white film. They had color film back then, but developing and printing it in a high school darkroom was not workable in 1978.
You may be thinking… What use in this digital age is a lesson about 1978 black and white film photography? Hold on. There is a usable lesson here.
One day we were assigned to shoot landscapes and my teacher taught us this. Look at a black and white photo, and you’ll notice that a sunny blue sky is almost always completely washed out to a complete blank. This makes our photos – well – boring. What you want is to darken that blue sky down – not to black, just to give it a little more detail. He told us we could use a red color filter (or red cellophane, or the red plastic off a broken LED clock) to accomplish this. This caused even the whispiest clouds to pop out in the photo and become interesting.
I will show you how to do this in GIMP.
First, my original photo from my iPhone. Nothing special, just a shot from my morning walk.
Nothing too amazing, now in GIMP, I will desaturate it.
Note that the sky and clouds are kinda washed out. This effect was MUCH WORSE in 35mm film photography.
Now, I used this filter on the original color image…
…making sure to set all 3 settings (shadows, midtones, highlights) to 0, -100, -100. I took the resulting red image and used desaturate on it again…
Wow, look at that sky pop out now!