What is a gradient map? It’s an adjustment layer that converts the tones of your image to the whatever gradient you have. You don’t have to work with grayscale images. While you can use gradient maps to color-correct and make adjustments, we’re going use it to make stuff funky.
(I’m using Photoshop CS6 here. It works similarly in newer versions. Photopea can also make gradient maps, using the same method)
I’ve got a selection of images here to show what works well with an gradient map and what doesn’t. For comparison of how it works with b&w and with color, the cat and the right-hand picture of Sophie are in color. I’ve already adjusted some of them to have a greater range of grays. I’ve also put what colors I want to use in my swatches, although I ended up lightening the dark brown.
In the layers panel, under new adjustment layer, select gradient map. It’ll come up weth a default black & white gradient.
In the properties panel, double click on the gradient itself. Now you can click or drag your swatches, going approximately from dark to light, to add them in. You can select the foreground or background color in the stops section (you’ll have to click off the gradient map layer to pick new colors or else you can only work in grayscale), or double-click on the stop to use the color picker.
Play around with the position of the stops and midpoints until you’re happy. You’ll see on the examples, the greater gradation of grays in a section the better it’ll look, and things with flat colors, like cartoons, don’t work well, nor things with high contrast – although there are ways around the latter, which we’ll get to.
You’re not limited to keeping it in normal mode either (when you’re doing it for color-correcting and fixing, changing the mode seems to be very useful from the tutorials I skimmed).
I do a lot of comic icons, and right now I’m doing the early issues of 2000ad, which are black and white. So here’s some ways of dealing with the high contrast problem.
This icon use a gradient map under all the textures – here it is:
Here it is bigger. You can see that the black and white are not very pure.
The variation in white and black helps the gradient map assign more colors, most effectively in the dark grays. One thing I did so it’d be more interesting was using a darker color for the white that matched the atmosphere (or lack there of since it’s in space).
Here’s an attempt to highlight more of the light greys with the gradient map, but it’s not super effective. It mostly looks muddy.
But once I added a subtle paper texture, it was much better. It no longer looks oversharpened or jaggy but there’s some variation in the very light areas.
And here’s a less contrast-y version so there’s less emphasis on the dark areas.
It takes a fair amount of fiddling to get it looking good, but I hope this helps you start using this technique and gives you some ideas.
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