# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1444603522 -7200
# Node ID c37a282541e392007747a5b881773b2cbe195aec
# Parent  4a75d044c6447b4e2ffa34589498f08f098e9d20
Fixed scaling calculations; added explicit support to preserve the aspect ratio.

diff -r 4a75d044c644 -r c37a282541e3 optimiser.py
--- a/optimiser.py	Sun Oct 11 23:23:26 2015 +0200
+++ b/optimiser.py	Mon Oct 12 00:45:22 2015 +0200
@@ -112,6 +112,8 @@
 
 -W - Indicate the output width (default is 320)
 -C - Number of colours per scanline (default is 4)
+-A - Produce an output image with the same aspect ratio as the input
+     (useful for previewing)
 
 -s - Saturate the input image (optional float, 1.0 if unspecified)
 -d - Desaturate the input image (optional float, 1.0 if unspecified)
@@ -133,8 +135,8 @@
 """ % split(sys.argv[0])[1]
         sys.exit(1)
 
-    base_width = 320
-    height = 256
+    base_width = width = 320
+    base_height = height = 256
 
     input_filename, output_filename = sys.argv[1:3]
     basename, ext = splitext(output_filename)
@@ -146,6 +148,10 @@
 
     width = get_parameter(options, "-W", int, base_width, base_width)
     number_of_colours = get_parameter(options, "-C", int, 4, 4)
+    preserve_aspect_ratio = "-A" in options
+
+    scale_factor = float(width) / base_width
+    height = int(base_height * scale_factor)
 
     # Preprocessing options that employ parameters.
 
@@ -169,12 +175,13 @@
     if make_image or preview:
         exif = EXIF.process_file(open(input_filename))
         im = PIL.Image.open(input_filename).convert("RGB")
-        im = rotate_and_scale(exif, im, base_width, height, rotate)
+        im = rotate_and_scale(exif, im, width, height, rotate)
+        image_width, image_height = im.size
 
-        # Scale images to the appropriate width.
+        # Scale images to the appropriate height.
 
-        if width != base_width:
-            im = im.resize((width, height))
+        if scale_factor != 1:
+            im = im.resize((image_width, int(image_height / scale_factor)))
 
         process_image(im, saturate, desaturate, darken, brighten)
 
@@ -183,16 +190,28 @@
     if preview:
         imp = im.copy()
         if half_resolution_preview:
-            imp = imp.resize((width / 2, height))
+            imp = imp.resize((image_width / 2, image_height))
         convert_image(imp, 8)
         if half_resolution_preview:
-            imp = imp.resize((width, height))
+            imp = imp.resize((image_width, image_height))
+
+        # Scale images to a height determined by the aspect ratio.
+
+        if preserve_aspect_ratio and scale_factor != 1:
+            imp = imp.resize((image_width, image_height))
+
         imp.save(preview_filename)
 
     # Generate an output image if requested.
 
     if make_image:
         convert_image(im, number_of_colours, least_error)
+
+        # Scale images to a height determined by the aspect ratio.
+
+        if preserve_aspect_ratio and scale_factor != 1:
+            im = im.resize((image_width, image_height))
+
         im.save(output_filename)
 
     # Verify the output image (which may be loaded) if requested.