A beginners question to clarify something I am trying to do it MATLAB regarding an image

Question

Sam 2011-8-3

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I am trying to learn how to use MATLAB so therefore am a complete beginner, I am sorry if this question is very basic or I do not use the correct terms/explain myself properly as I have no programming experience and I am finding it quite difficult to understand the help guide and textbook I have.

So I have created three variables for the colour bands by typing

Image_red=Image(:,:,1); Image_green=Image(:,:,2); Image_blue=Image(:,:,3);

and I can display one (eg red) by typing

figure, imagesc(Image_red), colormap(‘gray’)

The textbook I am working through then starts with the following instructions on using a variable to control the band selection.

Type >>band=1;

Then type >>Image_new=Image(:,:,band);

We will still get the red band in the new image. If we set band=2 then we would get the green band..

Write a new function called ‘draw1band.m’ which uses two input variables: an image name and another variable called ‘band’ to draw a grayscale image of either of the 3 bands. Once written, you should be able to type:

>>draw1band(‘srgmatlab’, 3)

And get a figure of the blue band.

I can't for the life of me figure out how to do this! Could anyone offer any help please? Thank you in advance. Sam

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Jan 2011-8-3

Please post what you have done so far and ask a specific question.

Reading the Getting Started sections of the documentation will help to learn the basics.

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Answer 1

Florin Neacsu 2011-8-3

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Hi,

Have a look at "function". type

doc function

In this case you need something like:

function [] = draw1band(inputImage,band)
%maybe sanity checks for band and inputImage
oneCh=inputImage(:,:,band);
figure
imagesc(oneCh);
colormap gray;
end

You need to save this as an .m file. You can do this in many ways. Maybe try :

edit draw1band

Feel free to have a look at the FAQ page http://matlab.wikia.com/wiki/FAQ

Regards, Florin

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Answer 2

Paulo Silva 2011-8-3

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Simple code to show one image and each rgb components on different axes

    name='ngc6543a.jpg';
    subplot(411)
    rgb = imread(name);
    imagesc(rgb); title(['RGB image ' name])
    for band=1:3
    subplot(4,1,band+1)
    im=rgb(:,:,band);
    imagesc(im); title(['Image using band=' num2str(band)])
    colormap('gray')
    end

Now one possible function

    function draw1band(Iname,band)
    %example use from MATLAB documentation
    %Iname='ngc6543a.jpg';
    %band=1;
    subplot(211)
    rgb = imread(Iname);
    imagesc(rgb); title(['RGB image ' Iname])
    subplot(212)
    im=rgb(:,:,band);
    imagesc(im); title(['Image using band=' num2str(band)])
    colormap('gray')
    end