Add option that prevents aspect ratio changes when downscaling

src/reCBZ/__main__.py

@@ -191,6 +191,11 @@ def main():
         dest="size_str",
         type=str,
         help="rescale images to the specified resolution")
+    images_group.add_argument( "--keepratio",
+        default=None,
+        dest="keep_ratio_when_downscaling",
+        action="store_true",
+        help="keep aspect ratio with --size")
     images_group.add_argument( "--noup", # rescale_group
         default=None,
         dest="no_upscale",

src/reCBZ/archive.py

@@ -23,6 +23,22 @@
 SOURCE_NAME:str = 'Source'
 chapter_prefix:str = 'v' # :) :D C:
 
+def get_ratio_preserving_size(provided_size):
+    # derived from https://pillow.readthedocs.io/en/stable/_modules/PIL/Image.html#Image.thumbnail (HPND)
+    def round_aspect(number, key):
+        return max(min(math.floor(number), math.ceil(number), key=key), 1)
+
+    x, y = provided_size
+
+    aspect = self.width / self.height
+    if x / y >= aspect:
+        x = round_aspect(y * aspect, key=lambda n: abs(aspect - n / y))
+    else:
+        y = round_aspect(
+            x / aspect, key=lambda n: 0 if n == 0 else abs(aspect - x / n)
+        )
+    return x, y
+
 
 def write_zip(savepath, chapters):
     new_zip = ZipFile(savepath,'w')
@@ -128,13 +144,17 @@ def convert_page_worker(source, options, savedir=None):
         if page.landscape:
             new_size = new_size[::-1]
         n_width, n_height = new_size
+        if options['keep_ratio']:
+            resize_size = get_ratio_preserving_size(new_size)
+        else:
+            resize_size = new_size
         # downscaling
         if (width > n_width and height > n_height
             and not options['nodown']):
-            img = img.resize((new_size), config.RESAMPLE_TYPE)
+            img = img.resize((resize_size), config.RESAMPLE_TYPE)
         # upscaling
         elif not options['noup']:
-            img = img.resize((new_size), config.RESAMPLE_TYPE)
+            img = img.resize((resize_size), config.RESAMPLE_TYPE)
 
     LossyFmt.quality = options['quality']
 
@@ -248,6 +268,7 @@ def __init__(self, filename:str):
         self._page_opt['format'] = get_format_class(config.img_format)
         self._page_opt['quality'] = config.img_quality
         self._page_opt['size'] = config.img_size
+        self._page_opt['keep_ratio'] = config.keep_ratio
         self._page_opt['grayscale'] = config.grayscale
         self._page_opt['noup'] = config.no_upscale
         self._page_opt['nodown'] = config.no_downscale

src/reCBZ/config.py

@@ -29,6 +29,7 @@
 img_format:str = _cfg["image"]["img_format"]
 img_quality:int = _cfg["image"]["img_quality"]
 img_size:tuple = _cfg["image"]["img_size"]
+keep_ratio:bool = _cfg["image"]["keep_ratio"]
 no_upscale:bool = _cfg["image"]["no_upscale"]
 no_downscale:bool = _cfg["image"]["no_downscale"]
 grayscale:bool = _cfg["image"]["grayscale"]

src/reCBZ/defaults.toml

@@ -35,6 +35,8 @@ img_format = ''
 img_quality = 80
 # new image width / height. set to 0,0 to preserve original dimensions
 img_size = [0,0]
+# preserve aspect ratio
+keep_ratio = false
 # set to True to disable upscaling of images smaller than resolution
 no_upscale = false
 # set to True to disable downscaling of images larger than resolution