smartcrop with libvips

smartcrop3.py

#!/usr/bin/python

# smartcrop with libvips, based very roughly on
# http://stackoverflow.com/a/1517178/894763

import sys

from gi.repository import Vips

image = Vips.Image.new_from_file(sys.argv[1])

class Rect:
    def __init__(self, left, top, width, height):
        self.left = left
        self.top = top
        self.width = width
        self.height = height

    def intersect(self, other):
        left = max(self.left, other.left)
        right = min(self.left + self.width, other.left + other.width)
        top = max(self.top, other.top)
        bottom = min(self.top + self.height, other.top + other.height)

        return Rect(left, top, right - left, bottom - top)

    def union(self, other):
        left = min(self.left, other.left)
        right = max(self.left + self.width, other.left + other.width)
        top = min(self.top, other.top)
        bottom = max(self.top + self.height, other.top + other.height)

        return Rect(left, top, right - left, bottom - top)

    def crop(self, image):
        return image.crop(self.left, self.top, self.width, self.height)


# how much off square is this image?
off_square = max(image.width, image.height) - min(image.width, image.height)

# trim the longer axis down in 10 steps, taking the lower-entropy end each time
step = int(off_square / 10.0)

while image.width != image.height:
    off_square = max(image.width, image.height) - min(image.width, image.height)
    if off_square < 2 * step:
        this_step = off_square
    else:
        this_step = step

    if image.width > image.height:
        r1 = Rect(0, 0, this_step, image.height)
        r2 = Rect(this_step, 0, image.width - 2 * this_step, image.height)
        r3 = Rect(image.width - this_step, 0, this_step, image.height)
    else:
        r1 = Rect(0, 0, image.width, this_step)
        r2 = Rect(0, this_step, image.width, image.height - 2 * this_step)
        r3 = Rect(0, image.height - this_step, image.width, this_step)

    ent1 = r1.crop(image).hist_find().hist_entropy()
    ent3 = r3.crop(image).hist_find().hist_entropy()

    if ent1 > ent3:
        select = r2.union(r3)
    else:
        select = r1.union(r2)

    image = select.crop(image)

image.write_to_file(sys.argv[2])