Hi,

I am just working a an alternative posterization algorithm. The basic difference is that the channel values are not fixed, like: 0, 0.25, 0.5, 0.75, 1, but algorithm is allowed to pick own values based on values in image.

As by now it is a crude python script, slow of course, but easy to tinker with... Later on it could be reworked to gimp plugin.

I am not sure if such algorithm exists and is available in gimp, and whether there is an interest....

Below are couple of examples. Each one is split, right side is posterized, left one is original. Also see a text on the images to learn the level of posterization and also generated custom values...

I would welcome any feedback

Well, I just added simple "dithering", that is passing remainders to the next pixel in line, so to show an effect I am attaching one of above images in dither mode. I just emphasize, it is posterization level 2 - 8 colors in total

EDIT: the intensity of dithering is controllable, so I am attaching two images to show it...

You can color-index an image using your own color map.

These are two different techniques...

Of course indexation with 8 colors provides better results then this my posterization of level 2 - that gives 8 colors as well, yet my posterization provides better results than "standard" posterization.

I am just testing an interest, if any....

=EDIT=

Just a note: I am working on it because I like the technical aspects of this technique, though I must say I have no use for it personally

I found the posterize filter quite limited, also because it jumps from a too small number of colurs to a far to huge skipping all intermediate values.

And i found a couple of scripts ( one from Saulgoode ...i think the other from RobA) that to me are a better alternative

About your implementation ... i don't know i think will mainly depend on user interactivity ,from how much and how easily could be controlled the number of colors , and chosen the colors.

I think may be interesting , for further manipulation a option to have each color on its own layer
(i.e. to outline each color blocth, or to soften the transitions etc)

It looks promising and interesting at least in reading the description and seeing the "work in progress" snapshots attached.
Anyway, whatever will be the final result, every effort aimed to improve GIMP with useful plugins is always appreciable and welcome according to me.

i made a thread about posterization versus indexed colours a couple of weeks ago

viewtopic.php?f=9&t=8726

maybe thats of interest to you

Thanks for all feedbacks, in general, I found out nothing new. I think that this technics is not very perspective. Peoples would prefer algorithm that creates let us say 7 distinct colors and not 7^3 colors

Anyway, python script exists - anybody can contact me for it, or if anybody has any ideas...

Yet, I attach last example - I have a 'force B/W' option in my script where algorithm force 0 and 255 values for each channel, so if level of posterization is 2, as here on this photo, all colors are combination of 0 and 255 values, so basically 8 colors are used here in this example (zoom in to verify )

Well I borrowed the photo from this page (the head only, I failed to find a link for entire image) and the result is attached.

In fact I just added posterization in LAB to my script, obviously colors are much less distorted in LAB mode then in RGB mode.

Of course no modification were done before neither after posterization...

And another example of LAB posterization

you can find the original image here:
http://de.pasani.wikia.com/wiki/Boyevan ... _01tfk.jpg


you see i dont really understand much of the technical stuff you are talking about
i like the posterization effect and use it sometimes and as you can see from the link that i posted, there are some people who would be interested in your work
i mean there is a whole forum dedicated to people who like to do stencil graffiti, and they will probably be very happy with your plug-in

so why dont you just post it, so people can try it ?
i would certainly appreciate it !

Allright, here is the link to my google drive

But this is not a gimp plugin! So far it is python script, so you need linux machine (preffereably), python3.0+, numpy and colormath (python module, install with 'easy_install colormath').

Read top of the file for more instructions.

Yes, it is no much usage-friendly, but this is a prototype...

LAB mode is very slow, but even-posterizer.py can processes images in batch mode that is a compensation for a speed to some degree.

=EDIT=

All scripts are available via subversion:



(this will put the files into current directory)

Another approach you can try is vector simplication. I used Autotrace (no longer works in Win7; have my handy-dandy XP VM though). Can also try using the tracing capabilities within Inkscape.

In the meantime I did some changes and improvments to my scripts, prepared a homepage: http://code.google.com/p/python-posteri ... troduction with examples and instructions for download and use.


Just note, they are python scripts so linux is almost a must... Also, they are slow, very slow...

Below are two examples where "cleaning" was used to remove discrete spots and so on