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82 lines
3.2 KiB
Python
82 lines
3.2 KiB
Python
import numpy as np
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import scipy.ndimage as nd
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def profile_line(img, src, dst, linewidth=1,
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order=0, mode='constant', cval=0.0):
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"""Return the intensity profile of an image measured along a scan line.
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Parameters
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----------
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img : 2d or 3d array
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The image, in grayscale (2d) or multichannel (2d + c) format.
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src : 2-tuple of numeric scalar (float or int)
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The start point of the scan line.
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dst : 2-tuple of numeric scalar (float or int)
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The end point of the scan line.
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linewidth : int, optional
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Width of the scan, perpendicular to the line
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order : int in {0, 1, 2, 3, 4, 5}, optional
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The order of the spline interpolation to compute image values at
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non-integer coordinates. 0 means nearest-neighbor interpolation.
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mode : string, one of {'constant', 'nearest', 'reflect', 'wrap'}, optional
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How to compute any values falling outside of the image.
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cval : float, optional
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If `mode` is 'constant', what constant value to use outside the image.
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Returns
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-------
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return_value : array
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The intensity profile along the scan line. The length of the profile
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is the ceil of the computed length of the scan line.
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Examples
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--------
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>>> x = np.array([[1, 1, 1, 2, 2, 2]])
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>>> img = np.vstack([np.zeros_like(x), x, x, x, np.zeros_like(x)])
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>>> img
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array([[0, 0, 0, 0, 0, 0],
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[1, 1, 1, 2, 2, 2],
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[1, 1, 1, 2, 2, 2],
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[1, 1, 1, 2, 2, 2],
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[0, 0, 0, 0, 0, 0]])
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>>> profile_line(img, (2, 1), (2, 5))
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array([ 1., 1., 2., 2.])
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"""
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src_row, src_col = src = np.asarray(src, dtype=float)
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dst_row, dst_col = dst = np.asarray(dst, dtype=float)
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d_row, d_col = dst - src
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theta = np.arctan2(d_row, d_col)
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length = np.ceil(np.hypot(d_row, d_col))
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line_col = np.linspace(src_col, dst_col, length)
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line_row = np.linspace(src_row, dst_row, length)
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# this if clause is necessary to keep the line centered on the true
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# source and destination points. Otherwise, the computed line has
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# an offset of `linewidth/2`
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if linewidth <= 1:
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perp_lines = np.array([line_row[:, np.newaxis],
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line_col[:, np.newaxis]])
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else:
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col_width = linewidth * np.sin(-theta) / 2
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row_width = linewidth * np.cos(theta) / 2
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perp_rows = np.array([np.linspace(row_i - row_width, row_i + row_width,
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linewidth) for row_i in line_row])
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perp_cols = np.array([np.linspace(col_i - col_width, col_i + col_width,
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linewidth) for col_i in line_col])
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perp_lines = np.array([perp_rows, perp_cols])
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if img.ndim == 3:
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pixels = [nd.map_coordinates(img[..., i], perp_lines,
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order=order, mode=mode, cval=cval)
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for i in range(img.shape[2])]
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pixels = np.transpose(np.asarray(pixels), (1, 2, 0))
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else:
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pixels = nd.map_coordinates(img, perp_lines,
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order=order, mode=mode, cval=cval)
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intensities = pixels.mean(axis=1)
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return intensities
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