Re: Color Matching to small set of fixed colors.

Alessandro Sabatelli Fri, 25 Jan 2008 19:41:03 -0800

The histogram operation patch uses the vImage framework to "match" thehistogram of one image to another. The matching process isapproximate. For further details reference the vImage programming guide.

For your purpose you may want to write a CIFilter which does the exactmapping you need.

.xX


On Jan 22, 2008, at 6:19 AM, David Giovannini <[EMAIL PROTECTED]> wrote:

Hello,

The color-map preserves luminance. The colors I am picking from aretruly fixed - including luminance and saturation. I have a black,dark gray and white. So all dark-grayish colors, regardless of hue,needs to go to the fully unsaturated dark gray.

The histogram operation, I think, is close. If I am not mistaken, itwill generate new colors based on different combos of intensities inthe map. Is this true?

So maybe use colormap to sort out the hues, and then use a secondarytwo dimensional color map of saturation vs luminance. This assumesthat I want to apply the same saturation and luminance regardless ofhue. These are lego colors. I can probably get away with that.


Cheers,
Dave

On Jan 22, 2008, at 4:38 AM, Alessandro Sabatelli wrote:

CIColorMap

<http://developer.apple.com/documentation/GraphicsImaging/Reference/CoreImageFilterReference/Reference/reference.html#//apple_ref/doc/filter/ci/CIColorMap>


<Color Map.qtz>


.xX


On Jan 16, 2008, at 8:44 AM, Alex Drinkwater wrote:

As I understand it, each channel has 256 possible values (0 > 255).

So, your lookup table should contain some kind of gradient, from 0to 255, across each of the R, G, B and A channels. To limit yourpalette, you'd probably have to pixellete each of the gradients,so that instead of 256 possible values in each channel, you mighthave, say, 64, or 32, or maybe even fewer. This would limit thepalette of available colours.


Something like this would do the job.

<LUT03.png>

The only problem is, it's hard to see what the actual coloursyou're likely to get are...

The other option of course, is to compile and use the HistogramOperation plugin, that's found in the Developer Examples folder(do a search for it).



Hope this makes sense.

alx




On 16 Jan 2008, at 16:26, David Giovannini wrote:

Hello,

I am having trouble seeing in my head what the lookup table/image/texture looks like.

The 0..n and n..255 will contain the black and the white. Howare the other colors distributed? The components are operating onthe same table row. How do I adjust the 256 values to select fromthe limited pallet?


Thank you,
Dave

On Jan 16, 2008, at 9:15 AM, Alex Drinkwater wrote:

What I failed to mention of course, is that the lookup
table has to be a strip with a width of 256 pixels. It
only needs to be 1 pixel high.

alx



--- Alex Drinkwater <[EMAIL PROTECTED]> wrote:

The code would be a little different in CIKernel
Slang, as texture coordinates are handled
differently.

This code does a similar thing, in CIKernel slang:


kernel vec4 lut(sampler image, sampler LUT)
{
   // Input pixel
   vec4 inPix = unpremultiply(sample(image,
samplerCoord(image)));
   // Output pixel
   vec4 outPix;
   outPix.r = unpremultiply(sample(LUT, vec2(inPix.r *
255.0,0.0))).r;
   outPix.g = unpremultiply(sample(LUT, vec2(inPix.g *
255.0,0.0))).g;
   outPix.b = unpremultiply(sample(LUT, vec2(inPix.b *
255.0,0.0))).b;
   outPix.a = unpremultiply(sample(LUT, vec2(inPix.a *
255.0,0.0))).a;

   // Output
   return premultiply(outPix);
}

alx


--- vade <[EMAIL PROTECTED]> wrote:

I would suggest creating a look up table as a
texture, feed that in to
a CIKernel, and have it map the r/g/b vales to the
r/g/b values of the
original image, something in GLSL like:

// define our rectangular texture samplers
uniform sampler2DRect tex0;
uniform sampler1D tex1;

// define our varying texture coordinates
varying vec2 texcoord0;
varying vec2 texcoord1;

void main (void)
{
   vec4 inputColor = texture2DRect(tex0, texcoord0);

   vec4 colorout;

   colorout.r = texture1D(tex1, inputColor.r).r;
   colorout.g = texture1D(tex1, inputColor.g).g;
   colorout.b = texture1D(tex1, inputColor.b).b;
   colorout.a = inputColor.a;

   gl_FragColor = colorout;
}


On Jan 15, 2008, at 10:10 PM, David Giovannini
wrote:

Hello,

Let me describe what I am trying to do a little

better than before.

Every avenue I try comes up short.

My daughter got a LEGO Mosaic set for Christmas.

am working on a

pattern maker application using QC. I have the

pixellating and LEGO

impressions all working. The mosaic set comes

with

12 colors where

three are black, dark gray, and white. I need to

have the colors in

the resulting image limited to the 12.

I keep trying to solve this problem using core

image kernels and not

getting the results I am looking for. I keep

looking for "grayish"

and attempting to find either the correct color

or

the correct gray.

There is nothing linear about the LEGO colors

and

"grayish" is very

subjective

Given a set of 12 arbitrary colors, with fixed

HBS, how would I

color match an image?

Any thoughts would be appreciated.

Cheers,
Dave

On Jan 13, 2008, at 12:40 PM, Stephanie

Giovannini

wrote:

Hello,

I am nearly done with a composition but I am

stuck solving a color

matching problem. I want to apply a palette of

fixed colors

(intensity, luminosity, saturation, etc all

predetermined) to an

image. The palette includes 3 greys. ColorMap

seems to  be close

but not quite.

What should I be using?

Cheers,
Dave


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