chang6.py

#!/usr/bin/env python

# A riff on https://gist.github.com/celoyd/dddc2f9e0ad7217a13e5

from skimage import io
from skimage.transform import resize
import numpy as np
from sys import argv

MAXINT = np.iinfo(np.uint8).max

# We'll use floats as an intermediate type, and
# skimage likes them always in the range -1..1:
def byte_to_unit(n):
  return n/MAXINT
  
def unit_to_byte(n):
  return np.clip(
    n * MAXINT,
    0,
    MAXINT
  ).astype(np.uint8)

src = io.imread(argv[1]) # Load our input image as 2D greyscale.

# Ensure we are working with the kind of image we think we're working with.
if src.ndim != 2:
    print "Input file isn't 2D. Can't work with this, sorry."
    exit(1)


# The major filter in the image forms a green checkerboard pattern, so create a mask to match.
green_mask = np.tile( np.array([[False,True],[True,False]]), (src.shape[0]/2, src.shape[1]/2))

# While green-filtered pixels exist on each row, red and blue pixels alternate rows.
# This means we can reuse the green mask but we must invert it. 
# Blue will get one set of alternating rows, red the other.

# Zero out the masks
blue_mask = np.zeros(green_mask.shape, dtype=bool) 
red_mask = np.zeros(green_mask.shape, dtype=bool)

# Project alternating rows from the inverted green mask
blue_mask[::2] = ~green_mask[::2]
red_mask[::-2] = ~green_mask[::-2]


# Initialize our image layers and then copy the masked data from the source image to each.

green_layer = np.zeros_like(src)
green_layer[green_mask] = src[green_mask]

blue_layer = np.zeros_like(src)
blue_layer[blue_mask] = src[blue_mask]

red_layer = np.zeros_like(src)
red_layer[red_mask] = src[red_mask]


# Assemble our layers into something we can work with.
dst = np.dstack([
  red_layer,
  green_layer,
  blue_layer
])


RED, GREEN, BLUE = (0, 1, 2)

# Tone down the green a bit.
dst[:,:,GREEN] /= 2

dst = byte_to_unit(dst.astype(np.float32))

input_width, input_height = src.shape  # Expecting a 2D array here!

dst = resize(dst, (input_width/2, input_height/2))
dst *= 4
dst[:,:,BLUE] *= 1.75 # Totally arbitrary but seems to fix the blue!
dst = unit_to_byte(dst)

io.imsave(argv[2], dst)