How to get the pixels intersected with a vector line?

Question

Lavender Liu 2016-3-24

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回答： Reza Teimoori 2021-3-3

I would like to get the image pixels which intersect with a vector line . As shown in the figure below, I would like to get the yellow pixels; the starting coordinates (x1,y1) and ending coordinates (x2,y2) of the vector line are known. Could anybody help me to solve this question? I used matlab sometimes but not well.

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Answer 1

Image Analyst 2016-3-24

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在 MATLAB Online 中打开

You can use linspace and round the coordinates. Be sure to have enough points so that you don't skip any pixels. But when you do that you might have duplicate pixels that you have to remove. Here's the demo:

m = zeros(11,7)
imshow(m, 'InitialMagnification', 1600);
axis on;
axis image;
grid on;
x1 = 1;
y1 = 7;
x2 = 7;
y2 = 5;
% Create a line from point 1 to point 2
spacing = 0.4;
numSamples = ceil(sqrt((x2-x1)^2+(y2-y1)^2) / 0.4)
x = linspace(x1, x2, numSamples)
y = linspace(y1, y2, numSamples)
xy = round([x',y'])
dxy = abs(diff(xy, 1))
duplicateRows = [0; sum(dxy, 2) == 0]
% Now for the answer:
finalxy = xy(~duplicateRows,:)
finalx = finalxy(:, 1);
finaly = finalxy(:, 2);
% Plot the points
hold on;
plot(finalx, finaly, 'y*');

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Answer 2

Walter Roberson 2016-3-24

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That looks like a job for improfile()

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Answer 3

Reza Teimoori 2021-3-3

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If you are looking for an accurate and fast method you have to employ a so-called ray-tracing approach such as this one. Most of them try to find the intersection of the line with planes (rather than pixels). This way you would be reducing your problem's dimensionality from

to

in 2D and from

to

in 3D.