# reducing resolution of an image

Asked by kash on 9 May 2012
Latest activity Commented on by 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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Answer by Geoff on 9 May 2012

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.

Answer by 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')
```

## 1 Comment

Walter Roberson on 9 May 2012

That would seem to be increasing the resolution, rather than decreasing the resolution.

Answer by 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

## 1 Comment

Walter Roberson on 9 May 2012

Seems like an expensive way of reducing the resolution...

Answer by 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));
```

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 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 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.