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From: Ying Li on 22 Dec 2009 16:54
Hi All,

I am wondering is there any algorithm that you can get eh the pixels with same RGB value in a picture very quickly.

Any hints will be appreciated. Thanks a lot!!

Merry Christmas,
Ying
From: Andy on 22 Dec 2009 17:08
"Ying Li" <liyingapply(a)hotmail.com> wrote in message <hgrf5s$bn6$1(a)fred.mathworks.com>...
> Hi All,
>
> I am wondering is there any algorithm that you can get eh the pixels with same RGB value in a picture very quickly.
>
> Any hints will be appreciated. Thanks a lot!!
>
> Merry Christmas,
> Ying

I'm pretty sure you could use SplitVec to do something like this: http://www.mathworks.com/matlabcentral/fileexchange/24255-consecutive-vector-spliter
From: ImageAnalyst on 22 Dec 2009 17:26
Ying:
first you have to construct your 3D color gamut, and then you have to
inspect it to look for elements with a count greater than 1, meaning
more than one pixel has that color. You can get the color gamut like
this:

gamut3D = zeros(256,256,256);
lastRow = sizeOfImage(1);
lastCol = sizeOfImage(2);
for row = 1 : lastRow
for col = 1: lastCol
redValue = originalImage(row, col, 1) + 1; % Convert from 0-255 to
1-256
greenValue = originalImage(row, col, 2) + 1; % Convert from 0-255 to
1-256
blueValue = originalImage(row, col, 3) + 1; % Convert from 0-255 to
1-256
gamut3D (redValue, greenValue, blueValue) = gamut3D (redValue,
greenValue, blueValue) + 1;
end
end

Then just scan it looking for >1. I think you can do this:
(r,g,b) = find(gamut3D > 1);
Then you have a list of all RGB colors where more than one pixel has
that color. Now you loop over all colors to find the x,y locations
for k = 1:length(r)
redValue = r(k);
greenValue = g(k);
blueValue = b(k);
% Use the find() command to find pixels (i.e. the pixel x,y
coordinates) where the original image's red value = redValue, etc.
Details are very simple and left as an exercise for you.
end
From: ImageAnalyst on 22 Dec 2009 17:28
Just as aside -- you might be interested in this article:

%-------------------------------------------------------------------------------
% http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?tp=&arnumber=4421050&isnumber=4420928
% Introduction of frequency image and applications
% Kashiwagi, T. Oe, S.
% Tokushima Prefectural Ind. Technol. Center, Tokushima;
%
% This paper appears in: SICE (Society of Instrument and Control
Engineers), 2007 Annual Conference
% Publication Date: 17-20 Sept. 2007
% On page(s): 584-591
% Location: Takamatsu,
% ISBN: 978-4-907764-27-2
% INSPEC Accession Number: 9853526
% Digital Object Identifier: 10.1109/SICE.2007.4421050
% Current Version Published: 2008-01-07
%
% Abstract
% We introduce a new imaging method of "Frequency Image" and its
applications.
% This new image is made from multi-dimensional features of an image
and presents
% a distribution of the frequency of feature vectors. Especially,
selecting R, G and B colors
% as the three features of an image, Frequency Image is a feature
image of which pixel
% represents the frequency of the same color pixels. In this paper,
first, we explain
% the basic idea and how to make this Frequency Image. Next, we
introduce some effective
% applications using this image. Finally we mention excellent
potentials of Frequency Images.
%-------------------------------------------------------------------------------
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