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https://github.com/wassname/scikit-image.git
synced 2026-08-12 12:30:16 +08:00
Add (bi-)cubic interpolation
This commit is contained in:
Johannes Schönberger
@@ -1,12 +1,19 @@
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cdef inline double nearest_neighbour(double* image, int rows, int cols,
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double r, double c, char mode,
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double cval)
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cdef inline double nearest_neighbour_interpolation(double* image, int rows,
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int cols, double r,
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double c, char mode,
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double cval)
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cdef inline double bilinear_interpolation(double* image, int rows, int cols,
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double r, double c, char mode,
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double cval)
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cdef inline double cubic_interpolation(double x, double[4] f)
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cdef inline double bicubic_interpolation(double* image, int rows, int cols,
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double r, double c, char mode,
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double cval)
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cdef inline double get_pixel(double* image, int rows, int cols, int r, int c,
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char mode, double cval)
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@@ -5,16 +5,17 @@
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from libc.math cimport ceil, floor, round
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cdef inline double nearest_neighbour(double* image, int rows, int cols,
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double r, double c, char mode,
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double cval):
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cdef inline double nearest_neighbour_interpolation(double* image, int rows,
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int cols, double r,
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double c, char mode,
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double cval):
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"""Nearest neighbour interpolation at a given position in the image.
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Parameters
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----------
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image : double array
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Input image.
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rows, cols: int
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rows, cols : int
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Shape of image.
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r, c : int
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Position at which to interpolate.
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@@ -23,6 +24,11 @@ cdef inline double nearest_neighbour(double* image, int rows, int cols,
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cval : double
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Constant value to use for constant mode.
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Returns
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-------
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value : double
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Interpolated value.
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"""
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return get_pixel(image, rows, cols, <int>round(r), <int>round(c),
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@@ -38,7 +44,7 @@ cdef inline double bilinear_interpolation(double* image, int rows, int cols,
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----------
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image : double array
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Input image.
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rows, cols: int
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rows, cols : int
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Shape of image.
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r, c : int
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Position at which to interpolate.
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@@ -47,6 +53,11 @@ cdef inline double bilinear_interpolation(double* image, int rows, int cols,
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cval : double
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Constant value to use for constant mode.
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Returns
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-------
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value : double
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Interpolated value.
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"""
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cdef double dr, dc
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cdef int minr, minc, maxr, maxc
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@@ -64,6 +75,79 @@ cdef inline double bilinear_interpolation(double* image, int rows, int cols,
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return (1 - dr) * top + dr * bottom
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cdef inline double cubic_interpolation(double x, double[4] f):
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"""Ccubic interpolation.
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Parameters
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----------
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x : double
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Position in the interval [0, 1].
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f : double[4]
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Function values at positions [0, 1/3, 2/3, 1].
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Returns
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-------
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value : double
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Interpolated value.
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"""
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return \
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f[1] + 0.5 * x * \
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(f[2] - f[0] + x * \
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(2.0 * f[0] - 5.0 * f[1] + 4.0 * f[2] - f[3] + x * \
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(3.0 * (f[1] - f[2]) + f[3] - f[0])))
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cdef inline double bicubic_interpolation(double* image, int rows, int cols,
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double r, double c, char mode,
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double cval):
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"""Bicubic interpolation at a given position in the image.
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Parameters
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----------
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image : double array
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Input image.
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rows, cols : int
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Shape of image.
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r, c : int
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Position at which to interpolate.
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mode : {'C', 'W', 'R'}
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Wrapping mode. Constant, Wrap or Reflect.
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cval : double
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Constant value to use for constant mode.
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Returns
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-------
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value : double
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Interpolated value.
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"""
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cdef int r0 = <int>r
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cdef int c0 = <int>c
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if r < 0:
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r0 -= 1
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if c < 0:
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c0 -= 1
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# scale position to range [0, 1]
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cdef double xr = (r - r0 + 1) / 3
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cdef double xc = (c - c0 + 1) / 3
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cdef double fc[4], fr[4]
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cdef int pr, pc
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for pr in range(r0 - 1, r0 + 3):
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# do row-wise cubic interpolation
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for pc in range(c0 - 1, c0 + 3):
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fc[pc + 1 - c0] = get_pixel(image, rows, cols, pr, pc, mode, cval)
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fr[pr + 1 - r0] = cubic_interpolation(xc, fc)
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# do cubic interpolation for interpolated values of each row
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return cubic_interpolation(xr, fr)
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cdef inline double get_pixel(double* image, int rows, int cols, int r, int c,
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char mode, double cval):
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"""Get a pixel from the image, taking wrapping mode into consideration.
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@@ -72,7 +156,7 @@ cdef inline double get_pixel(double* image, int rows, int cols, int r, int c,
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----------
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image : double array
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Input image.
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rows, cols: int
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rows, cols : int
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Shape of image.
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r, c : int
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Position at which to get the pixel.
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@@ -81,6 +165,11 @@ cdef inline double get_pixel(double* image, int rows, int cols, int r, int c,
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cval : double
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Constant value to use for constant mode.
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Returns
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-------
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value : double
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Pixel value at given position.
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"""
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if mode == 'C':
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if (r < 0) or (r > rows - 1) or (c < 0) or (c > cols - 1):
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