Create Palette Image with Multiple Rows Using ImageMagick

Question

I have learned how to generate a palette image from a source image using ImageMagick:

convert source.png -colors 256 -unique-colors -scale 1000% palette.png

An image with a single row of colors, such as the following, is output:

However, I would like set a value to limit the number of squares/columns, & start a new row when that number is reached. So the output should look more like this:

Is it possible to do this with ImageMagick? Or is there another method to do so?

Answer 1

What you can do, for example, is crop the long line into 4 parts (each of 25%), and then join them one under the other (-append):

convert source.png -colors 256 -unique-colors -scale 1000% \
 -crop 25%x100% -append palette.png

This is not quite what you asked for, but by varying the percentage you can vary the crop point, or you can use a fixed width in pixels, like -crop 63x100% to get exactly the example output you provided.