Backstory: I am designing the pattern in PhotoShop of a quilt my wife is making. The quilt is made of 15x20 squares of exactly six shades of blue - dark at one end to light at the other end. The gradient will be "noisy". I want to experiment with that noise.

So, I have an image that is 15x20 pixels, and I have reduced the palette to exactly 6 colours.

The problem is that, with an exact palette I can't apply any filters such as the noise filter. It's just not available. Dead-end.

I tried Posterize, but Posterize chooses its own colours, often choosing grey. Another dead-end.

The attached sample was done manually. I want a truer noisy gradient that I can experiment with.


enter image description here


@Billy Kerr:

This is what I get when I follow your directions exactly.

enter image description here

I started with an RGB image, and I'm using PS CC.

I've experimented with every one of the settings - and that is the best I get.


You could do something similar to this, semi automatically.

Create a simple gradient between the darkest and lightest blue and apply it to your 15*20px image.

Something like this:

enter image description here

Do Image > Mode > Indexed, and choose the settings shown:

enter image description here

  • Thanks, I hadn't tried local palette. Now that I have I didn't get anything resembling what you did, it was way too non-random, but I'll experiment. Dec 13 '20 at 0:15
  • @DaveC426913 - Hmm, make sure you start with an RGB image, the results may be dependent on what version of Photoshop you have. This is Photoshop CC
    – Billy Kerr
    Dec 13 '20 at 0:17
  • I am using Photoshop CC and starting with an RBG image. Dec 13 '20 at 4:02
  • +1 I was thinking Index Mode as well. @DaveC426913 are you setting the Dither to Noise? I get pretty much the same image as Billy.
    – Scott
    Dec 13 '20 at 6:28
  • Yes. Dither=Noise. Dec 13 '20 at 18:29

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