draw a line on an image

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Fatma Gargouri 2011-10-3

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评论： Walter Roberson 2021-1-12

采纳的回答： Fangjun Jiang

Hello

I want draw a line on an image, just by giving the coordinates of the extremities.

I tryed the function line(...) but it didn't give me the right result

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Fangjun Jiang 2011-10-3

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Pay attention of the syntax of line().

line([x1,x2],[y1,y2]), not line([x1,y1],[x2,y2]);

figure(1);line([0 1],[0 1]); will show a line

figure(2);line([0 0],[1 1]); won't show a line

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Amber Elferink 2021-1-11

you have to do hold off at the end again (for next viewers)

Walter Roberson 2021-1-12

I suspect Sumit either wanted to know about getframe() https://www.mathworks.com/help/matlab/ref/getframe.html or else wanted to know how to draw a line directly into an array with the intent to save the array as an image but without having to display on the screen.

The easiest way to draw a line directly into an array is to use Computer Vision Toolbox insertShape()

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David Young 2011-10-3

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在 MATLAB Online 中打开

Perhaps your problem is that figure coordinates and array indices have different conventions. So, for example

imshow(im)
line([50 100], [30 30])

draws a line from im(30, 50) to im(30, 100).

Arrays are indexed by (ROW,COLUMN). Positions in a figure are addressed by (X,Y). When you display an array as an image, using the usual conventions, ROW corresponds to Y and COLUMN corresponds to X.

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Somsubhro Chaudhuri 2017-8-16

编辑：Somsubhro Chaudhuri 2017-8-16

Test7_extended_1139x967_test.zip

Thank you @Image Analyst. I managed doing that now. I now have a binary image with a line between two points (attached). Could you please suggest a way to only change the area right below the line to black?

I was thinking of defining the equation of the line, and then running a for loop to cover these pixels, but I want to enquire about a shorter way of doing this as I'll have to run this code for a very large number of images.

Thank you! Regards, Somsubhro

Image Analyst 2017-8-16

You could take the endpoints of the line, then add on the bottom of the image coordinates, then call poly2mask() to get a binary image mask. Then use that to erase the image in that quadrilateral.

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