MATLAB Answers

Downsampling an image

92 views (last 30 days)
Venkat R
Venkat R on 5 Apr 2011
Hi everybody,
I want to downsample a 49x49 image into 7x7 image using gaussian filter of 31x31. The alternate approach I tried (but not getting the accurate result) is as follows.
Any help is very much appreciated.
with regards, Venkat
clear all,clc
I = imresize(imread('pout.tif'),[49 49]); % I used matlab image as example of 49x49 image instead of my experiment image
hgausspymd = video.Pyramid;
hgausspymd.PyramidLevel = 3;
I_down = mat2gray(double(step(hgausspymd, I)));
Image Analyst
Image Analyst on 17 Sep 2011
Exactly what does "accurate" mean to you? As David says the final output image will be nearly all edge effects since very little will fit the 31x31 filter. There are a variety of ways to take edge effects into account. Which way do you prefer? Which way are you using when you define accuracy?

Sign in to comment.

Answers (2)

Oliver on 17 Sep 2011
  1 Comment
Walter Roberson
Walter Roberson on 17 Sep 2011
That would downsample to 25 x 25 rather than 7 x 7, and would not use a gaussian filter as asked by the original poster.

Sign in to comment.

Venkat R
Venkat R on 18 Sep 2011
Dear friends, thanks for your comments.
I am using the following code.
"accurate" means, should be able to summarize the information content in 49x49 images. Not just the peak/central regions etc
h = fspecial('gaussian',[31 31],3.5);
idown= imfilter(bw4,h,'symmetric');
bw4 is a 17x17 matrix. If I take first 7 alternative values in it, it is serving me the purpose
with regards, Venkat

Community Treasure Hunt

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

Start Hunting!

Translated by