reducing resolution of an image

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

Answer 1

[Geoff]

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.

Answer 2

[Jessica Lam]

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')

Ref: http://www.mathworks.com.au/help/techdoc/ref/print.html

[Walter Roberson]

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

Answer 3

[Jessica Lam]

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

[Walter Roberson]

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

Answer 4

[Walter Roberson]

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]

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]

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]

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.