profile_line function

[Jaime Lopez Carvajal]

Hi, 

I would like to know why the function profile_line from profile.py in module skimage.measure, always return an additional value (zero value) at the end for horizontal and vertical lines, and two extra values (2 zeros) for diagonal lines.

I mean, if I have an image 10x10, and I want the profile line

> a = profile_line(img, (0, 0), (0, 10))

> array([  83.,   82.,   81.,   88.,   95.,   88.,   93.,  107.,  121.,  146.,    0.])

and with diagonal lines it returns two additional values (2 zeros), like this:

> a = profile_line(img, (0, 0), (10, 10))

> array([  83.,   92.,  105.,  123.,  100.,   69.,   46.,   46.,   48.,   52.,   62.,   70.,   77.,   84.,    0.,    0.])

Thanks in advance for your comments, 

Jaime

[Juan Nunez-Iglesias]

Hi Jaime,

It's a bit confusing, but, because profile_line is used in interactive tools, *the final point is included in the line*, unlike normal Python/NumPy indexing. It would be unintuitive in interactive tools *not* to include the final point. (This is in the "Notes" section in the docstring.) So, your final point, (0, 10), is actually outside your image, and the constant value of 0 is returned. I suspect that for your use case you want to call profile_line(img, (0, 0), (0, 9)) and profile_line(img, (0, 0), (9, 9)). I think it should work as expected in those cases.

I hope that helps!

Juan.

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[Jaime Lopez Carvajal]

Hi Juan,

I see your point, I read about the difference with Numpy indexing, but I did understand at that time. 

Your explanation is very clear, as well your suggestion about to use the shorter range.

Thanks for your time.

Jaime