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reducing resolution of an image

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kash
kash on 9 May 2012
I have an image having resolution of 256x256,i want to reduce the resolution of image to 128x128,64x64,without using imresize conmmand please help

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Answers (4)

Geoff
Geoff on 9 May 2012
Think about it...
If you half the width and height, that means each group of 2x2 pixels becomes one pixel. You average the pixel intensities for each block and set that as your new pixel.
Well, you don't have to average them. You could select one or do any number of statistics on the chunk. But you should start simple.
The rest is just loops and matrix indexing. I'm sure you can cope with that.

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Jessica Lam
Jessica Lam on 9 May 2012
you may try the following code. for resolution of 470 X 274
set(gcf,'PaperUnits','inches','PaperPosition',[0 0 4.7 2.74])
print('-dpng', 'filename.png', '-r100')

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Walter Roberson
Walter Roberson on 9 May 2012
That would seem to be increasing the resolution, rather than decreasing the resolution.

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Jessica Lam
Jessica Lam on 9 May 2012
just change the vector of PaperPosition from [ 0 0 4.7 2.74 ] to something you want
for example [0 0 1.28 1.28] for 128x128 or [0 0 0.64 0.64] for 64X64

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Walter Roberson
Walter Roberson on 9 May 2012
Seems like an expensive way of reducing the resolution...

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Walter Roberson
Walter Roberson on 9 May 2012
t = fft2(YourImage);
t(:,end/2+1:end) = [];
t(end/2+1:end,:) = [];
SmallerImage = ifft2(t);
or
t = reshape(YourImage, 2, size(YourImage,1)/2, 2, size(YourImage,2)/2, 2);
SmallerImage = cast(permute(mean(permute(mean(t,3),[1 2 4 3]),1),[1 2 3],[2 3 1]),class(YourImage));

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kash
kash on 9 May 2012
Walter for your first code,i get only figure wingow white in coloue and no image displayed,and for second code i get error
Error using ==> reshape
To RESHAPE the number of elements must not change.
my image is cameraman.tif
Walter Roberson
Walter Roberson on 9 May 2012
For the first one, you might need to use
SmallerImage = cast(ifft2(t), class(YourImage));
For the second one it looks like I had an additional 2:
t = reshape(YourImage, 2, size(YourImage,1)/2, 2, size(YourImage,2)/2);
kash
kash on 9 May 2012
walter getting same white figure window ,image is same not displaying ,warning as
Warning: Displaying real part of complex input.
for the next one i get error as
Error using ==> permute
Too many input arguments.

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