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How to keep all image data after transformation?

Asked by Mohammad Al Nagdawi on 1 Mar 2018
Latest activity Commented on by Mohammad Al Nagdawi on 8 Mar 2018
In the below code, I try to calculate the distance between the 1-pixel and the other 0's pixels within a4 matrix. I face a problem because the 1-pixel is disappeared from the matrix after transformation, therefore, the err4 values becomes inf for all.
h = 120;
v = 80 ;
r=20;
row = 200;
col = 300;
T = [1 0 0;
0 1 0;
h v 1];
tform = affine2d(T);
%create mask
a4 = zeros(row,col);
%set one control point (cp) for mask
a4(row/5*4,col/5*4) = 1;
cb_ref = imref2d(size(a4));
%Apply transformation same as ourput floating image.
b4 = imrotate(a4,r);
b4 = imwarp(b4,tform,'OutputView', cb_ref); % refrence space relative with another image.
%calculte the error matrix
err4 = bwdist(b4);
How can allow the matrix to grow after transformation to keep the 1-pixel?

  5 Comments

r is rotation value such as 20 degrees and cb_ref is reference space relative to another image in the same size. This is registration algorithm between two images and very hard to post my whole code
That doesn't help. Without code to define cb_ref, we can't run your code, and the comments aren't enough for me to figure out what's happening. So all I can say now is to make sure that b4 is a 2-D logical (binary) image.
I update my question to define cb_ref and r

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1 Answer

Answer by Image Analyst
on 4 Mar 2018

I don't know what your plans are for the warping, but after you warped the image, the dot disappeared:
clc; % Clear the command window.
close all; % Close all figures (except those of imtool.)
clear; % Erase all existing variables. Or clearvars if you want.
workspace; % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 15;
h = 120;
v = 80 ;
r=20;
row = 200;
col = 300;
T = [1 0 0;
0 1 0;
h v 1];
tform = affine2d(T);
%create mask
a4 = zeros(row,col);
%set one control point (cp) for mask
a4(row/5*4,col/5*4) = 1;
% Display the image.
subplot(2, 2, 1);
imshow(a4, []);
title('a4 Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0, 0.04, 1, 0.96]);
% Apply transformation same as output floating image.
b4 = imrotate(a4, r);
% Display the image.
subplot(2, 2, 2);
imshow(b4, []);
title('b4 Image', 'FontSize', fontSize, 'Interpreter', 'None');
cb_ref = imref2d(size(a4));
b4 = imwarp(b4, tform, 'OutputView', cb_ref); % reference space relative with another image.
% Calculate the error matrix
% Display the image.
subplot(2, 2, 3);
imshow(b4, []);
title('b4 Warped Image', 'FontSize', fontSize, 'Interpreter', 'None');
err4 = bwdist(b4);
% Display the image.
subplot(2, 2, 4);
imshow(err4, []);
title('err4 Image', 'FontSize', fontSize, 'Interpreter', 'None');

  7 Comments

because bwdist is the easiest method to calc the distance between the 1-pixel in original position and its new position after transformation - in case it exists.
But it's new position is not in the image. You did something after rotation so that the point is not there. That's what my demo showed.
Actually, keep the 1-pixel within the image is very important ... therefore I ask for a way to keep the image extend with transformation to display the pixel.

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