diff --git a/wagtail/wagtailimages/models.py b/wagtail/wagtailimages/models.py
index c561cdcc5..99d732efb 100644
--- a/wagtail/wagtailimages/models.py
+++ b/wagtail/wagtailimages/models.py
@@ -1,5 +1,4 @@
 import os.path
-import re
 
 from six import BytesIO
 
@@ -21,7 +20,7 @@ from unidecode import unidecode
 from wagtail.wagtailadmin.taggable import TagSearchable
 from wagtail.wagtailimages.backends import get_image_backend
 from wagtail.wagtailsearch import indexed
-from .utils import validate_image_format
+from wagtail.wagtailimages.utils import validate_image_format, parse_filter_spec
 
 
 @python_2_unicode_compatible
@@ -144,49 +143,6 @@ class Filter(models.Model):
     """
     spec = models.CharField(max_length=255, db_index=True)
 
-    OPERATION_NAMES = {
-        'max': 'resize_to_max',
-        'min': 'resize_to_min',
-        'width': 'resize_to_width',
-        'height': 'resize_to_height',
-        'fill': 'resize_to_fill',
-        'original': 'no_operation',
-    }
-
-    def __init__(self, *args, **kwargs):
-        super(Filter, self).__init__(*args, **kwargs)
-        self.method = None  # will be populated when needed, by parsing the spec string
-
-    def _parse_spec_string(self):
-        # parse the spec string and save the results to
-        # self.method_name and self.method_arg. There are various possible
-        # formats to match against:
-        # 'original'
-        # 'width-200'
-        # 'max-320x200'
-
-        if self.spec == 'original':
-            self.method_name = Filter.OPERATION_NAMES['original']
-            self.method_arg = None
-            return
-
-        match = re.match(r'(width|height)-(\d+)$', self.spec)
-        if match:
-            self.method_name = Filter.OPERATION_NAMES[match.group(1)]
-            self.method_arg = int(match.group(2))
-            return
-
-        match = re.match(r'(max|min|fill)-(\d+)x(\d+)$', self.spec)
-        if match:
-            self.method_name = Filter.OPERATION_NAMES[match.group(1)]
-            width = int(match.group(2))
-            height = int(match.group(3))
-            self.method_arg = (width, height)
-            return
-
-        # Spec is not one of our recognised patterns
-        raise ValueError("Invalid image filter spec: %r" % self.spec)
-
     def process_image(self, input_file, backend_name='default'):
         """
         Given an input image file as a django.core.files.File object,
@@ -195,17 +151,16 @@ class Filter(models.Model):
         """
         backend = get_image_backend(backend_name)
 
-        if not self.method:
-            self._parse_spec_string()
+        method_name, method_arg = parse_filter_spec(self.spec)
 
         # If file is closed, open it
         input_file.open('rb')
         image = backend.open_image(input_file)
         file_format = image.format
 
-        method = getattr(backend, self.method_name)
-
-        image = method(image, self.method_arg)
+        # Call method
+        method = getattr(backend, method_name)
+        image = method(image, method_arg)
 
         output = BytesIO()
         backend.save_image(image, output, file_format)
diff --git a/wagtail/wagtailimages/utils.py b/wagtail/wagtailimages/utils.py
index 2f0c0e676..00c5476cd 100644
--- a/wagtail/wagtailimages/utils.py
+++ b/wagtail/wagtailimages/utils.py
@@ -1,4 +1,5 @@
 import os
+import re
 
 from PIL import Image
 
@@ -26,3 +27,38 @@ def validate_image_format(f):
         # Check that the internal format matches the extension
         if image.format.upper() != extension.upper():
             raise ValidationError(_("Not a valid %s image. Please use a gif, jpeg or png file with the correct file extension.") % (extension.upper()))
+
+
+# TODO: Cache results from this method in something like Python 3.2s LRU cache (available in Django 1.7 as django.utils.lru_cache)
+def parse_filter_spec(filter_spec):
+    # parse the spec string and save the results to
+    # self.method_name and self.method_arg. There are various possible
+    # formats to match against:
+    # 'original'
+    # 'width-200'
+    # 'max-320x200'
+
+    OPERATION_NAMES = {
+        'max': 'resize_to_max',
+        'min': 'resize_to_min',
+        'width': 'resize_to_width',
+        'height': 'resize_to_height',
+        'fill': 'resize_to_fill',
+        'original': 'no_operation',
+    }
+
+    # original
+    if filter_spec == 'original':
+        return OPERATION_NAMES['original'], None
+
+    # width/height
+    match = re.match(r'(width|height)-(\d+)$', filter_spec)
+    if match:
+        return OPERATION_NAMES[match.group(1)], int(match.group(2))
+
+    # max/min/fill
+    match = re.match(r'(max|min|fill)-(\d+)x(\d+)$', filter_spec)
+    if match:
+        width = int(match.group(2))
+        height = int(match.group(3))
+        return OPERATION_NAMES[match.group(1)], (width, height)