Ordered dithering with a set amount of colors?

[snibgo]

"-dither" is a setting. It doesn't change images. It only affects operations such as "-colors" and "-remap" that reduce the number of colours. It doesn't affect "-posterize" or "-ordered-dither" operations.

The default dither method is "Riemersma". If you don't want dithering in those operations, "+dither" turns it off.

By contrast, "-ordered-dither" is an operation that changes an image.

So, yes, they are different beasts.

And -ordered-dither means -ordered-dither -posterize 2

No.

In my view, the best way to learn IM is to play wth it. Read the documentation, but also write loads of scripts.

[plshelpx_x]

What I don't understand, is why -ordered-dither can't be a setting like -dither. Is it just that IM doesn't work that way or are there no viable way of implementing an ordered dither "function" that can use palettes of your choosing?

I just want something like -dither Riemersma, but instead of being random scattered dots it's neatly organized, aka "ordered".

[fmw42]

Perhaps you want something like this -- http://www.imagemagick.org/Usage/quanti ... one_offset

[snibgo]

What I don't understand, is why -ordered-dither can't be a setting like -dither.

"-dither" is merely a setting that applies to some colour-reduction operations. The setting determines how error is to be diffused.

"-ordered-dither" is a colour-reduction operation that does not diffuse errors.