Photoshop: how to create a stepped gradient without blurred separation?

Question

I'm trying to create a stepped gradient with Photoshop from black to white made of vertical bands. I can more or less achieve this by using the posterize feature but the cut between colors is not neat.

This is what I get:

Each time the gradient goes from one color to the next one, I get a line of another color. I have posterized the picture with 50 steps which means that I should only have 50 colors but when I check them programmatically I get 344 colors because of those lines.

Is there another way of creating a neat stepped gradient with Photoshop without the blur between the colors? Posterize with only 4 to 10 colors work but beyond that, I get a blur.

Is there another feature from Photoshop I should use?

Thanks

Laurent

Answer 1

A simple way of making sure you only have a certain number of colors in a gradient is to create the gradient in a document that only has as many pixels as you want colors.

So if you for example want 23 colors, you create a document with the dimensions 23 × 1 px.

Then you select the colors you want as foreground and background color and add a linear Gradient Fill.

Afterwards you simply flatten the image and scale the image with Nearest Neighbor interpolation to the wanted size. Multiply the width with an integer to make sure all bands have the same width.

Here I've scaled the example image to 2000% × 16000% to get 20 × 160 px bands:

Answer 2

I think the problem is the posterize filter.

Instead, try converting to Indexed colour mode, set 50 colours, then convert back to RGB mode. Then export as PNG.

I tested this method, and checked the output using Image Magick, and it definitely shows only 50 colours.

If you've installed Image Magick the command to check the number of colours is as follows:

magick identify -format %k filename.png