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minimise colour palette and grouping colour, pixel image


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Iain Duke Giles

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ok , i really need some help,i have this image here (kinda hard to explain, bare with me),basically i want to be able to bring down the colour palette, so photoshop only uses 10 colours/shades of grey (ranging from 1=white to 10=black if you get me) to make up this pixelated image (attached), kinda like what you can do in illustrator when tracing/expanding images into vector (thats the first problem im really stuck on)….second is, i then want to separate each pixel/colour into its own layer eg, if there is 10 colours, then id end up with 10 layers one for each colour, can anybody help me out here?…
Untitled-2.jpg
 
Operations like this are done all the time in scientific, scientific graphing, and image processing applications such as Matlab, Mathematica, Origin, etc. If you happen to be familiar with any of these applications (or anything similar), this is almost certainly the most straightforward way to proceed.

In Matlab (or the open source clone of Matlab, "Octave"), the function to call is:
http://www.mathworks.com/help/matlab/ref/colormap.html

Obviously, you don't want colors -- you want a B&W palette. One of Matlab's standard palettes is "gray". However, eyeballing your image, it obviously has very different numbers of pixels in each of the gray levels, so, to get it to look really good, you probably would prefer a custom B&W palette. A nice description of how to optimize such plots for data with poor histogram equalization is here:

http://cresspahl.blogspot.com/2012/03/expanded-control-of-octaves-colormap.html
(scroll about half way down the page).

Note that many scientific plots want smooth gradations in color (or B&W tone) as the plotted function varies. In contrast, you want steps. This is also quite common, and is NBD to do in any of the above programs.

You also requested that the different tonal levels be placed on different layers. Again, this is easy in any of these programs-- just make a loop which marches through the different tonal ranges and produces a separate plot for each range, and then import them as different layers in a PS file.

I'm not sure of the context of your request. If you are going to be processing lots of images this way, one of the scientific apps is absolutely, without a doubt, the best way to proceed. OTOH, if this is a one-time deal, eg, for an artistic project or for a homework assignment in a PS class, obviously, you probably either can't use the above software, or don't want to bother learning it. In a case where you are absolutely constrained to work within Photoshop, I would suggest you make up 10 gradient maps (with contiguous boundaries), and place the output of each gradient map on a separate layer. I can also think of several other ways to do it within PS, but the gradient map method is probably the most flexible.

HTH,

Tom
 
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Thanks for this great info, it is for an art project, but if this works out ill probably end up doing a few....i will look into matlab, im just not sure how it will work out for me as it may be outside my skill level, but it sounds like its exactly what i need....but as you say the gradiant mapping in ps might be all i need, just depends what output i can get with it....thanks a billion man :)
 
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