#!/usr/bin/env python

# Copyright 2016-2019 Biomedical Imaging Group Rotterdam, Departments of
# Medical Informatics and Radiology, Erasmus MC, Rotterdam, The Netherlands
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import numpy as np


def linstretch(i, i_max=255, i_min=0):
    '''
    Stretch the input image i pixel values from i_min to i_max
    '''
    rmin = np.min(i.flatten())  # find the min. value of pixel in the image
    rmax = np.max(i.flatten())  # find the max. value of pixel in the image
    m = (i_max - i_min)/(rmax - rmin)  # find the slope of line joining point (0, 255) to (rmin,rmax)
    c = i_max - m*rmax  # find the intercept of the straight line with the axis
    i_stretch = m*i + c  # transform the image according to new slope

    return i_stretch
