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From: Rudra on 7 Apr 2010 02:27
ImageAnalyst <imageanalyst(a)mailinator.com> wrote in message <f4af3dae-0c89-4cbe-a2e3-0ef1abe06033(a)o30g2000yqb.googlegroups.com>...
> Rudra:
> Strange, it seems to work for me.
> You can type "doc colon" in the command window to get an explanation,
> but basically this is the standard MATLAB concept where you have
> startingValue:incrementValue:endingValue. You'd better learn this
> soon if you want to progress in your MATLAB programming. "end" is
> just a shortcut to getting the the last index value of the array so
> you don't actually have to find it out yourself with the size()
> function - it's just already there for you to use.
>
> You didn't post your code so no one can figure out where you messed
> up. So I made up some demo code for you to illustrate the concept.
> Note that if you have color images, you'll have to handle the third
> dimension - this demo is only for 2D gray scale images.
>
> Be sure to join any lines split into two by the newsreader.
>
> % Change the current folder to the folder of this m-file.
> % (The line of code below is from Brett Shoelson of The Mathworks.)
> if(~isdeployed)
> cd(fileparts(which(mfilename)));
> end
> clc; % Clear command window.
> clear all; % Delete all variables.
> close all; % Close all figure windows except those created by imtool.
> imtool close all; % Close all figure windows created by imtool.
> workspace; % Make sure the workspace panel is showing.
>
> % Read in standard MATLAB gray scale demo image.
> grayImage = imread('cameraman.tif');
> subplot(2, 2, 1);
> imshow(grayImage, []);
> title('Original Grayscale Image', 'FontSize', 20);
> set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.
> [rows columns numberOfColorBands] = size(grayImage);
> message = sprintf('For the original image:\n# Rows = %d\n# Columns = %d
> \n# Color Bands = %d', rows, columns, numberOfColorBands);
> uiwait(msgbox(message));
>
> % Sub-sample the image.
> oddSubSampledImage = grayImage(1:2:end, 1:2:end);
> subplot(2, 2, 3);
> imshow(oddSubSampledImage, []);
> title('Odd Sampled Image', 'FontSize', 20);
> [rowsOdd columnsOdd numberOfColorBandsOdd] = size(oddSubSampledImage);
> message = sprintf('For the odd image:\n# Rows = %d\n# Columns = %d\n#
> Color Bands = %d', rowsOdd, columnsOdd, numberOfColorBandsOdd);
> uiwait(msgbox(message));
>
> evenSubSampledImage = grayImage(2:2:end, 2:2:end);
> subplot(2, 2, 4);
> imshow(evenSubSampledImage, []);
> title('Even Sampled Image', 'FontSize', 20);
> [rowsEven columnsEven numberOfColorBandsEven] =
> size(evenSubSampledImage);
> message = sprintf('For the even image:\n# Rows = %d\n# Columns = %d\n#
> Color Bands = %d', rowsEven, columnsEven, numberOfColorBandsEven);
> uiwait(msgbox(message));


_________________________________________________________________
Thank you for all the replies:
To tell you what code I'm working on I'll paste the code below:
X = imread ('filename.png');
for j=1:400
for i=1:268
r=rem(i,2);
if r==0
a=X(j,i);
else
b=X(j,i);
end
end
end

I wrote this loop to put values of alternate pixels in the matrices a and b.
But the result is not what I intended for. The variables a and b behave as true variables that is when the loop is executed every time the value of a and b changes to the new pixel value and at last the last pixel value is only in it. I want to define a and b as matrixes, so that whenever the loop is executed the values of every iteration is stored one below the other so that I can extract any value by just typing
a(3) just to read the third value in the matrix. Can I do that plz help.
Thank You
From: ImageAnalyst on 7 Apr 2010 06:20
Either use my code and refer to the pixel using row,col coordinates,
or look at the subs2ind() and ind2subs() functions if you want linear
indexing (which I think you'll find less intuitive).
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