Extracting Raw Data From an Image in MATLAB
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% digitize.m
function [x,y] = digitize(imgname)
[img,map] = imread(imgname);
image(img);
colormap(map);
Left = input('Enter the left X coordinate: ');
Right = input('Enter the right X coordinate: ');
Bottom = input('Enter the bottom Y coordinate: ');
Top = input('Enter the top Y coordinate: ');
disp('Click on the lower-left corner');
[localLeft,localBottom] = ginput(1);
disp('Click on the upper-right corner');
[localRight,localTop] = ginput(1);
disp('Begin digitizing points. Click right mouse button when finished.');
b = 0; bold = 0;
while(b~=3)
[xp,yp,b] = ginput(1);
if (b == 1)
if (bold ~= 0)
line([xold; xp], [yold; yp]);
x = [x; xp];
y = [y; yp];
else
x = xp;
y = yp;
end
xold = xp; yold = yp; bold = b;
end
end
x = (x - localLeft) / (localRight-localLeft) * (Right-Left) + Left;
y = (y - localBottom) / (localTop - localBottom) * (Top-Bottom) + Bottom;
I want to know what is the logic behind the formula in getting x and y in the last two lines of the code.
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Answers (1)
Image Analyst
on 18 Apr 2013
They're getting an x and y in pixels, then getting rid of the offset (the pixel row and column where the axes are located) then scaling to the "real world" coordinates, i.e. the units of the graph rather than pixels.
2 Comments
Image Analyst
on 18 Apr 2013
Do you trust your user to click on the right point or not? Who's to say what's "right"?
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