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#!/usr/bin/env python3
# Copyright © 2014 Mattias Andrée (maandree@member.fsf.org)
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
# This module contains interpolation functions.
from curve import *
def linearly_interpolate_ramp(r, g, b): # TODO demo this
'''
Linearly interpolate ramps to the size of the output axes
@param r:list<float> The red colour curves
@param g:list<float> The green colour curves
@param b:list<float> The blue colour curves
@return :(r:list<float>, g:list<float>, b:list<float>) The input parameters extended to sizes of `o_size`,
or their original size, whatever is larger.
'''
C = lambda c : c[:] if len(c) >= o_size else ([None] * o_size)
R, G, B = C(r), C(g), C(b)
for small, large in ((r, R), (g, G), (b, B)):
small_, large_ = len(small) - 1, len(large) - 1
# Only interpolate if scaling up
if large_ > small_:
for i in range(len(large)):
# Scaling
j = i * small_ / large_
# Floor, weight, ceiling
j, w, k = int(j), j % 1, min(int(j) + 1, small_)
# Interpolation
large[i] = small[j] * (1 - w) + small[k] * w
return (R, G, B)
def cubicly_interpolate_ramp(r, g, b): # TODO demo this
'''
Interpolate ramps to the size of the output axes using cubic Hermite spline
@param r:list<float> The red colour curves
@param g:list<float> The green colour curves
@param b:list<float> The blue colour curves
@return :(r:list<float>, g:list<float>, b:list<float>) The input parameters extended to sizes of `o_size`,
or their original size, whatever is larger.
'''
C = lambda c : c[:] if len(c) >= o_size else ([None] * o_size)
R, G, B = C(r), C(g), C(b)
# Basis functions
h00 = lambda t : (1 + 2 * t) * (1 - t) ** 2
h01 = lambda t : t * (1 - t) ** 2
h10 = lambda t : t ** 2 * (3 - 2 * t)
h11 = lambda t : t ** 2 * (t - 1)
def tangent(values, index, last):
'''
Calculate the tangent at a point
@param values:list<float> Mapping from points to values
@param index:int The point
@param last:int The last point
@return :float The tangent at the point `index`
'''
if last == 0: return 0
if index == 0: return values[1] - values[0]
if index == last: return values[last] - values[last - 1]
return (values[index + 1] - values[index - 1]) / 2
# Interpolate each curve
for small, large in ((r, R), (g, G), (b, B)):
small_, large_ = len(small) - 1, len(large) - 1
# Only interpolate if scaling up
if large_ > small_:
for i in range(len(large)):
# Scaling
j = i * small_ / large_
# Floor, weight, ceiling
j, w, k = int(j), j % 1, min(int(j) + 1, small_)
# Points
pj, pk = small[j], small[k]
# Tangents
mj, mk = tangent(small, j, small_), tangent(small, k, small_)
# Interpolation
large[i] = h00(w) * pj + h10(w) * mj + h01(w) * pk + h11(w) * mk
## Check local monotonicity
eliminate_halos(r, g, b, R, G, B)
return (R, G, B)
def polynomially_interpolate_ramp(r, g, b): # TODO Speedup, demo and document this
'''
Polynomially interpolate ramps to the size of the output axes.
This function will replace parts of the result with linear interpolation
where local monotonicity have been broken. That is, there is a local
maximum or local minimum generated between two reference points, linear
interpolation will be used instead between those two points.
@param r:list<float> The red colour curves
@param g:list<float> The green colour curves
@param b:list<float> The blue colour curves
@return :(r:list<float>, g:list<float>, b:list<float>) The input parameters extended to sizes of `o_size`,
or their original size, whatever is larger.
'''
C = lambda c : c[:] if len(c) >= o_size else ([None] * o_size)
R, G, B, linear = C(r), C(g), C(b), [None]
for ci, (small, large) in enumerate(((r, R), (g, G), (b, B))):
small_, large_ = len(small) - 1, len(large) - 1
# Only interpolate if scaling up
if large_ > small_:
n = len(small)
## Construct interpolation matrix (TODO this is not working correctly)
M = [[small[y] ** i for i in range(n)] for y in range(n)]
A = [x / small_ for x in range(n)]
## Eliminate interpolation matrix
# (XXX this can be done faster by utilising the fact that we have a Vandermonde matrix)
# Eliminiate lower left
for k in range(n - 1):
for i in range(k + 1, n):
m = M[i][k] / M[k][k]
M[i][k + 1:] = [M[i][j] - M[k][j] * m for j in range(k + 1, n)]
A[i] -= A[k] * m
# Eliminiate upper right
for k in reversed(range(n)):
A[:k] = [A[i] - A[k] * M[i][k] / M[k][k] for i in range(k)]
# Eliminiate diagonal
A = [A[k] / M[k][k] for k in range(n)]
## Construct interpolation function
f = lambda x : sum(A[i] * x ** i for i in range(n))
## Apply interpolation
large[:] = [f(x / large_) for x in range(len(large))]
## Check local monotonicity
eliminate_halos(r, g, b, R, G, B)
return (R, G, B)
def eliminate_halos(r, g, b, R, G, B):
'''
Eliminate haloing effects in interpolations
@param r:list<float> The original red curve
@param g:list<float> The original green curve
@param b:list<float> The original blue curve
@param R:list<float> The scaled up red curve
@param G:list<float> The scaled up green curve
@param B:list<float> The scaled up blue curve
'''
linear = None
for ci, (small, large) in enumerate(((r, R), (g, G), (b, B))):
small_, large_ = len(small) - 1, len(large) - 1
## Check local monotonicity
for i in range(small_):
# Small curve
x1, x2, y1, y2 = i, i + 1, small[i], small[i + 1]
# Scaled up curve
X1, X2 = int(x1 * large_ / small_), int(x2 * large_ / small_)
Y1, Y2 = large[X1], large[X2]
monotone = True
if y2 == y1:
# Flat part, just make sure it is flat in the interpolation
# without doing a check before.
for x in range(X1, X2 + 1):
large[x] = y1
elif y2 > y1:
# Increasing
monotone = all(map(lambda x : large[x + 1] >= large[x], range(X1, X2))) and (Y2 > Y1)
elif y2 < y1:
# Decreasing
monotone = all(map(lambda x : large[x + 1] <= large[x], range(X1, X2))) and (Y2 < Y1)
# If the monotonicity has been broken,
if not monotone:
# replace the partition with linear interpolation.
# If linear interpolation has not yet been calculated,
if linear is None:
# then calculate it.
linear = linearly_interpolate_ramp(r, g, b)
# Extract the linear interpolation for the current colour curve,
# and replace the local partition with the linear interpolation.
large[X1 : X2 + 1] = linear[ci][X1 : X2 + 1]
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