How to calculate the gray value on a line segment

Using the above code can realize the gray value distribution on a line segment, but you must click with the mouse. Is there a method to directly specify the pixel coordinates? It's really difficult for beginners to do this. Thank you

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/images/ref/improfile.html#mw_d999001e-7e39-4285-8a79-2f1ffdcb5ce7

You can pass in the coordinates as the xi and yi parameters.

[tao wang]

Please give me an example. I read the help document, but I didn't get it out. Thank you

[Walter Roberson]

im = imread('cameraman.tif');
imshow(im)

%take a profile from x = 50 to x = 100 along y = 75
[sx, cy, c] = improfile(im, [50 100], [75 75])

sx = 51×1

50 51 52 53 54 55 56 57 58 59

cy = 51×1

75 75 75 75 75 75 75 75 75 75

c = 51×1

179 176 183 176 180 179 183 183 183 182

%cross-check it by indexing into the image to extract the content
im(75, 50:100)

ans = 1×51

179 176 183 176 180 179 183 183 183 182 186 189 193 133 24 17 16 16 15 15 16 13 13 15 16 16 16 17 17 16

You can see that the result of the indexing is the same as the c results, in this particular case where I extracted a horizontal line.

improfile is not restricted to extracting horizontal or vertical lines.

[tao wang]

Thank you for your answer. The values of the abscissa and ordinate above are increased by one, but if it is a straight line connected by two arbitrary points, how to express it in this case? I would be grateful if you could give a code example of this case

[Walter Roberson]

The values of the abscissa and ordinate above are increased by one

No they are not. I indexed at column 50:100 (which is 51 locations) and you can see that sx starts from exactly 50 and has length 51. Exactly the same values, nothing added to them.

but if it is a straight line connected by two arbitrary points

im = imread('cameraman.tif');
ny = size(im,1);
nx = size(im,2);
xstart = randi(nx)

xstart = 101

xend = randi(nx)

xend = 91

ystart = randi(ny)

ystart = 253

yend = randi(ny)

yend = 61

[sx, cy, c] = improfile(im, [xstart xend], [ystart yend])

sx = 193×1

101.0000 100.9479 100.8958 100.8438 100.7917 100.7396 100.6875 100.6354 100.5833 100.5312

cy = 193×1

253 252 251 250 249 248 247 246 245 244

c = 193×1

164 151 121 89 65 57 55 57 56 51

Notice that sx(1) is exactly the same as xstart, and the sy(1) is exactly the same as ystart. The values have not been increased by 1.

[tao wang]

thank you very much. I'll take a closer look when I get up tomorrow. I may still have something I don't understand. I'm a little stupid. I may even bother you (if you have time)