# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1444603730 -7200
# Node ID dac076310b26459a41cecd169c0148a3d5aaf569
# Parent  2ddb5ff4b7c921918934a41f9b4ec567117d94af# Parent  649cbff60e7c62b04b83967de6d1045bdd43f72d
Fixed scaling calculations; added explicit support to preserve the aspect ratio.

diff -r 2ddb5ff4b7c9 -r dac076310b26 optimiser.py
--- a/optimiser.py	Sun Oct 11 23:31:25 2015 +0200
+++ b/optimiser.py	Mon Oct 12 00:48:50 2015 +0200
@@ -108,6 +108,8 @@
 
 -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)
@@ -129,8 +131,8 @@
 """ % 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)
@@ -142,6 +144,10 @@
 
     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.
 
@@ -165,12 +171,13 @@
     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)))
 
         sim = SimpleImage(list(im.getdata()), im.size)
         process_image(sim, saturate, desaturate, darken, brighten)
@@ -181,12 +188,18 @@
     if preview:
         imp = im.copy()
         if half_resolution_preview:
-            imp = imp.resize((width / 2, height))
+            imp = imp.resize((image_width / 2, image_height))
         sim = SimpleImage(list(imp.getdata()), imp.size)
         convert_image(sim, 8)
         imp.putdata(sim.getdata())
         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.
@@ -195,6 +208,12 @@
         sim = SimpleImage(list(im.getdata()), im.size)
         convert_image(sim, number_of_colours, least_error)
         im.putdata(sim.getdata())
+
+        # 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.