manipulate pixels in an image

4 views (last 30 days)
J J
J J on 7 Jun 2011
Is there a way to include the neighboring pixels into a pixel - in other ways, to include 9 pixels into 1? I dont want to just zoom out, rather I need to adjust the pixel values accordingly and to decrease the amount of total pixels. Thanks in advance.

Sign in to answer this question.

Answers (4)

Image Analyst
Image Analyst on 7 Jun 2011
How about
smallerImage = largerImage(1:3:end, 1:3:end) % Subsamples
or to average instead of subsample:
smallerImage = conv2(single(largerImage), ones(3)/9, 'same'); % To average, but same size.
smallerImage = smallerImage (1:3:end, 1:3:end) % Then subsamples to resize.
You might want to cast smallerImage to uint8 if you want to display it with imshow().
Bjorn Gustavsson
Bjorn Gustavsson on 7 Jun 2011
Something like this will do it:
img_in = randn(36);
M = eye(size(img_in,1)/3);
idx = sort(repmat(1:size(M,1),3,1));
M = M(:,idx);
img_out = M*(M*img_in')'/9;
Obviously I haven't bothered comparing this with a straightforward looped algorithm, but this doesn't scale well att all with size...
...something like O(n^3) when I guess a looped should scale with O(n^2).
Titus Edelhofer
Titus Edelhofer on 7 Jun 2011
Hi,
if you have the image processing toolbox, you can use the function imresize.
Titus
  1 Comment
J J
J J on 7 Jun 2011
thx Titus; and if I dont (which is the case)? Is there a way to manually do it? a for loop is not preferred since there are many many pixels.

Sign in to comment.

Jonas Reber
Jonas Reber on 7 Jun 2011
if you don't have it you could take a look at e.g. http://www.mathworks.com/matlabcentral/fileexchange/4658-updownsample

Categories

Find more on Image Arithmetic in Help Center and File Exchange

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!