Image rotate - want white background instead of default black

Dear Matlabneers,

I am using the following code to make the background of a rotated image "white", instead of the "black" background that imrotate applies by default. However, it is giving me a dotted line around the rotated edge of the image. Does anyone have any ideas how to fix this?

gry = imrotate(img,90+x,'bilinear');
mgry = ~imrotate(true(size(img)),90+x,'bilinear');
gry(mgry&~imclearborder(mgry)) = 255;

Thanks for any help in advance.

Regards, Andy

Answer 1

[Image Analyst]

Here's what I'd try (untested):

Edit imrotate.m

>> edit imrotate.m

Find this line:

A = padarray(A,[2 2],0,'both');

Change the 0 to 255 or whatever fill value you want. Then save it as a new file, imrotate255.m, somewhere in your search path. Then call imrotate255() instead of the built-in imrotate().

[Andy]

Hi,

Thanks for your suggestion, I have done what you said and have made a new imrotate255 function and copied the relevant mex file with it. However, the background is still black. I also changed the following to 255 too:

   B = tformarray(A, T, R, [1 2], [1 2], outputSize, [], 255);

[Image Analyst]

Try putting it in the "C:\Program Files\MATLAB\R2013a\toolbox\images\images\" folder - same place as where imrotate lives. And did you also change the first line to

function varargout = imrotate255(varargin)

Those are the only things I can think of.

What if you didn't make any changes whatsoever (leave the fill value as 0)? All you did was to change the name of the m-file and the first line. Does it work in that case?

[Andy]

I have done all those things, now it is saying it cannot find that file:

Undefined function 'imrotate255' for input arguments of type 'uint8'.

Error in main (line 34)
gry = imrotate255(img, 90+x,'bilinear');

Isnt that toolbox directory automatically searched as a default path?

[Image Analyst]

Say

which -all imrotate255

and see what it says. The IP Toolbox should be on the path. Type path at the command line to verify.

[Andy]

>> which -all imrotate255
'imrotate255' not found.

I have checked the path and it is there. I just doesnt detect it. Maybe it is not a good idea to place it in the reserved folder.

Anyway I was able to run the function when it is put in the same folder as the main function, however, the problem is that the background is still black after changing 0 to 255 and also I tried changing zeros() to 255*ones() and 255.*ones()

Edit: Finally works now after increasing the padding also from [2 2] to [20 20]. Thanks!

[Patrick Tuohy]

This no longer seems to work, I can't find "A = padarray(A,[2 2],0,'both');"

Anyone know how else to solve this?

[Image Analyst]

@Patrick Tuohy, in R2021a, it's at line 146.

A = padarray(A,[2 2],0);

Simply search for "padarray" (without searching for the whole line) and you should find it.

Answer 2

[Mustafa Umit Arabul]

I have done the same thing using imwarp.m function. And mimicked the 'crop' option of imrotate.m using spatial reference.

function rotated_image = imrotate_white(image, rot_angle_degree)
    RA = imref2d(size(image));    
    tform = affine2d([cosd(rot_angle_degree)    -sind(rot_angle_degree)     0; ...
                      sind(rot_angle_degree)     cosd(rot_angle_degree)     0; ...
                      0                          0                          1]);

      Rout = images.spatialref.internal.applyGeometricTransformToSpatialRef(RA,tform);
      Rout.ImageSize = RA.ImageSize;
      xTrans = mean(Rout.XWorldLimits) - mean(RA.XWorldLimits);
      yTrans = mean(Rout.YWorldLimits) - mean(RA.YWorldLimits);
      Rout.XWorldLimits = RA.XWorldLimits+xTrans;
      Rout.YWorldLimits = RA.YWorldLimits+yTrans;

      rotated_image = imwarp(image, tform, 'OutputView', Rout, 'interp', 'cubic', 'fillvalues', 255);
  end

If you do not want to crop:

function rotated_image = imrotate_white(image, rot_angle_degree)
    tform = affine2d([cosd(rot_angle_degree)    -sind(rot_angle_degree)     0; ...
                      sind(rot_angle_degree)     cosd(rot_angle_degree)     0; ...
                      0                          0                          1]);

      rotated_image = imwarp(image, tform, 'interp', 'cubic', 'fillvalues', 255);
  end

[Mohamed Ibrahim]

thanks alot Mustafa

[Zsolt Kocsis]

Works fine, thank you!

[Jesús Díaz]

It works perfectly, thanks a lot.

[Celil Semih Sevincik]

thanks a lot

Answer 3

[Naveed Salman]

This is what I tried and it works well for me.

It doesn't require any m-file code. It can be written in Command line.

For white background this works

angle = 30;  % Specify angle
A = imread('My_Image.jpg');  % Specify your Image file
figure(1)
imshow(A)
B = imrotate(uint8(255*ones(size(A))),angle);
C = uint8(255*ones(size(B))) - B + imrotate(A,angle);
figure(2)
imshow(C)

If you want background of some other color you can modify it to this.

Background_color = [100 150 120];   % Specify background
angle = 30;   % Specify angle
A = imread('My_Image.jpg');  % Specify you Image file
figure(1)
imshow(A)
B = imrotate(uint8(ones(size(A))),angle);
C = uint8(ones(size(B))) - B;
C(:,:,1) = C(:,:,1)*Background_color(1);
C(:,:,2) = C(:,:,2)*Background_color(2);
C(:,:,3) = C(:,:,3)*Background_color(3);
C = C + imrotate(A,angle);
figure(2)
imshow(C)

[Image Analyst]

Why do you define

Background_color = [100 150 120];   % Specify background

yet use only 2 of the 3 elements of it?

C(:,:,2) = C(:,:,2)*Background_color(2);
C(:,:,3) = C(:,:,3)*Background_color(2);

You assign the second value (green, I guess) to both the green channel and the blue channel.

[Naveed Salman]

Thank @Image Analyst for pointing this mistake out.

The correct script is like this

C(:,:,1) = C(:,:,1)*Background_color(1);
C(:,:,2) = C(:,:,2)*Background_color(2);
C(:,:,3) = C(:,:,3)*Background_color(3);

I have editing my original mistake.