srsudar · April 11, 2016 20:59 · Apr 11, 2016
diff --git a/scale.py b/scale.py
@@ -0,0 +1,58 @@
+# -*- coding: utf-8 -*-
+"""
+Scale a PNG by an integer factor, keeping it pixelated.
+"""
+
+import png
+from sys import argv
+
+# We're assuming rgba for for ints per pixel. Looking at the pypng docs there
+# are other options this might be, but this is all I needed.
+VAL_PER_PIXEL = 4  # rgba
+
+if __name__ == '__main__':
+    # we expect scale_factor, in_file, out_file
+    if len(argv) != 4:
+        raise ValueError('Usage: scale_factor, in_file, out_file')
+
+    factor = int(argv[1])
+    in_file = argv[2]
+    out_file = argv[3]
+
+    reader = png.Reader(in_file)
+    content = reader.asDirect()
+    rows = content[2]
+
+    # content[2][0] assumes at least one row. There are original_width pixels in
+    # this row, and each pixel has VAL_PER_PIXEL ints for each pixel.
+    original_width = len(content[2][0]) / VAL_PER_PIXEL
+    original_height = len(content[2])
+
+    out_width = original_width * factor
+    out_height = original_height * factor
+
+    all_rows = []
+
+    # Iterate over each row. Each pixel is represented by several ints (the
+    # exact number depends on the file and is defined by VAL_PER_PIXEL). Each
+    # pixel must be grown by factor, and each row must then be appended factor
+    # number of times to all_rows.
+    for row in rows:
+        new_row = []
+        for num_pixel in range(len(row) / VAL_PER_PIXEL):
+            # / 4 for rgba
+            # if a single pixel row was [255, 128, 25, 0], we would want to
+            # expand that times 4.
+            pixel_start = num_pixel * VAL_PER_PIXEL
+            pixel_values = row[pixel_start:pixel_start + VAL_PER_PIXEL]
+            larger_values = list(pixel_values) * factor
+            new_row = new_row + larger_values
+        for i in range(factor):
+            # we've enlarged the row, now add it.
+            all_rows.append(new_row)
+
+    with open(out_file, 'w') as f:
+        # alpha = True for rgba. This will have to be updated for PNGs without
+        # alpha.
+        w = png.Writer(out_width, out_height, alpha=True)
+        w.write(f, all_rows)
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