convert whatever image to be a background

src/background.py

@@ -0,0 +1,71 @@
+#!/usr/bin/env python
+from PIL import Image
+
+class Background:
+    WIDTH = 400
+    HEIGHT = 300
+
+    def __init__(self, image):
+        self.image = image
+
+    @classmethod
+    def open(cls, filename):
+        return cls(Image.open(filename))
+
+    def convert(self):
+        self.resize()
+        self.crop()
+        self.dither()
+
+    # resize an image so that it's longest dimension is somewhere in the
+    # WIDTHxHEIGHT window, for further cropping down the line
+    def resize(self):
+        width, height = self.image.size
+
+        if width > height:
+            new_width = int(float(width) / height * self.HEIGHT)
+            new_height = self.HEIGHT
+        else:
+            new_width = self.WIDTH
+            new_height = int(float(height) / width * self.WIDTH)
+
+        self.image = self.image.resize(
+            (new_width, new_height),
+            resample=Image.LANCZOS,
+        )
+
+    # crop an image to WIDTHxHEIGHT in the center of whatever space is available
+    # in the image
+    def crop(self):
+        width, height = self.image.size
+
+        # we want a center crop, so we need to start the crop half the difference
+        # of the widths from the left edge, and half the difference of the
+        # heights from the top edge
+        left = abs(width - self.WIDTH) / 2
+        top = abs(height - self.HEIGHT) / 2
+        right = self.WIDTH + left
+        bottom = self.HEIGHT + top # we already resized to the output height
+
+        self.image = self.image.crop((left, top, right, bottom))
+
+    def dither(self):
+        # from https://github.com/pimoroni/inky/blob/75f12b415ad1ae42ac3be92b33f83f51519f5da3/examples/what/dither-image-what.py#L59
+        palette = Image.new('P', (1, 1))
+        palette.putpalette((255, 255, 255, 0, 0, 0, 255, 0, 0) + (0, 0, 0) * 252)
+
+        self.image = self.image.convert("RGB").quantize(palette=palette)
+
+    def show(self):
+        self.image.show()
+
+if __name__ == '__main__':
+    from argparse import ArgumentParser
+
+    parser = ArgumentParser(__file__)
+    parser.add_argument('filename', help='source image for the converted background')
+    args = parser.parse_args()
+
+    background = Background.open(args.filename)
+    background.convert()
+    background.show()