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Issue in plotting binary image boundaries with real axis values

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Hi,
I have extracted the image boundaries from binary image and mm). I am able to diplay the binary image with real axis values i.e. x1, y1, (which is in mm), However, while plotting the extracted boundaries, the axes values are displayed in the pixels. (as shown in the attachment of binary image boundary.bmp).. Have anyone encountered simiar problem before ??
A = imgaussfilt(grayImage,5);
A1 = imbinarize (A,1900); %% binary image conversion
ax = gca;
A2 = imagesc (x1, y1,A1); %% Display binary image
set(gca, 'YDir','normal')
[b,~] = bwboundaries(A1, 8); b1 = b{1}; %% boundary extraction from binary image
b2 = smoothdata (b1(:,2),'sgolay',25);
b3 = smoothdata(b1(:,1),'sgolay',25);
plot(b2,b3,'b'); axis equal %% Plot the extrcated boundary

Accepted Answer

Steve Eddins
Steve Eddins on 29 Jun 2021
The function bwboundaries returns boundary values in pixel coordinates. You'll need to scale those to world coordinates yourself. For this purpose, imref2d and intrinsicToWorld might be useful to you.
R = imref2d(imageSize,xWorldLimits,yWorldLimits)
[xWorld, yWorld] = intrinsicToWorld(R,xIntrinsic,yIntrinsic)
  3 Comments
Turbulence Analysis
Turbulence Analysis on 30 Jun 2021
Hi,
I treid as follows, now I can able to shift the psoition of zero and convert the pixel to mm with the scale factor.. !
b2 = smoothdata ((b1(:,2)/10)-40,'sgolay',35);
b3 = smoothdata((b1(:,1)/10),'sgolay',35);
ax = gca;
plot(b2 ,b3 ,'r');
axis equal

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More Answers (1)

Joseph Cheng
Joseph Cheng on 29 Jun 2021
so you'll need to find the conversion between pixel to linear xy (mm). sort of the mm/px scale factor + offset to 0;
from the looks of it half of the image (row or column) is 0,
xscale = (max(x1)-min(x1))/size(A,2); %mm/pixel
newb2 = (b2-size(A,2)/2)*xscale;
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