profile_line

[Jaime Lopez Carvajal]

HI friends,

I am having problems with profile_line function, because I want to get gray values following some coordinates, but it is given to me wrong gray values

that does not exist in the original image, like 128, 126 or 64.

image = np.array([[170, 170,  70,  70,  70,  70,  70,  70,  70,  70],
       [170, 170,  70,  70,  70,  70,  70,  70,  90,  70],
       [170, 170, 170,  70,  70,  70,  70,  70,  70,  70],
       [170, 170, 170,  70,  70,  70,  70,  70,  70,  70],
       [170, 170, 170,  70,  70,  70,  70,  70,  70,  70],
       [170, 170, 170, 170,  70,  70,  70,  70,  70,  70],
       [110, 170, 170, 170,  70,  70,  70,  70,  70,  70],
       [ 50, 170, 170, 170,  70,  70,  70,  70,  70,  10],
       [ 50,  50, 170, 170,  70,  70,  70,  70,  10,  10],
       [ 50, 110, 110, 110,  70,  70,  70,  70,  10,  10]], dtype=uint8)

coords = np.array([[70,  0],

       [70,  0],
       [71,  1],
       [71,  2],
       [72,  3],
       [72,  4],
       [73,  4],
       [74,  5],
       [74,  6],
       [75,  7],
       [75,  8],
       [76,  8],
       [77,  9]])

gray_values = profile_line(image,(0,0),(7,9)).astype(int)

gray_values

array([170, 170, 128, 126,  70,  70,  70,  70,  70,  70,  70,  64,  10])

but the correct values would be:
gray_values
array([170, 170, 170, 70, 70, 70, 70, 70, 70, 70, 70, 70, 70])

Do you know why this is happening? Any suggestion?

Thanks in advance, Jaime

[Jaime Lopez Carvajal]

Sorry, the correct coordinates are:

coords = np.array([[0, 0],

       [0, 0],
       [1, 1],
       [1, 2],
       [2, 3],
       [2, 3],
       [3, 4],
       [4, 5],
       [4, 6],
       [5, 6],
       [5, 7],
       [6, 8],
       [7, 9]])

[Juan Nunez-Iglesias]

No, those aren't the correct coordinates. ;)

profile_line ensures that the coordinates are spaced 1 pixel apart, and then performs interpolation (the "order" argument to the function) to find the values.

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[Jaime Lopez Carvajal]

Hi Juan,

Thanks, now I understand how it works.

Do you know how can I get the gray values without interpolation, just the raw gray values taken from original image?

Thanks in advance, Jaime

[Juan Nunez-Iglesias]

Hey Jaime,

Yes, if you set the interpolation order equal to 0, that resolves to nearest neighbor interpolation, so it will pick the value from the nearest pixel. The coordinates will still be fractional so that distances are preserved, though. I hope that's still useful to you! =)

Juan.

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[Jaime Lopez Carvajal]

Hi Juan,

Yeah, that is what I needed, no interpolation, so I will set it to 0.

Thanks, Jaime