new method alter(); 3 times faster generate()

src/PIL/ImageFilter.py

@@ -15,6 +15,8 @@
 # See the README file for information on usage and redistribution.
 #
 
+from __future__ import division
+
 import functools
 
 
@@ -323,12 +325,16 @@ class Color3DLUT(MultibandFilter):
     """
     name = "Color 3D LUT"
 
-    def __init__(self, size, table, channels=3, target_mode=None):
+    def __init__(self, size, table, channels=3, target_mode=None, **kwargs):
         self.size = size = self._check_size(size)
         self.channels = channels
         self.mode = target_mode
 
-        table = list(table)
+        # Hidden flag `_copy_table=False` could be used to avoid extra copying
+        # of the table if the table is specially made for the constructor.
+        if kwargs.get('_copy_table', True):
+            table = list(table)
+
         # Convert to a flat list
         if table and isinstance(table[0], (list, tuple)):
             table, raw_table = [], table
@@ -371,20 +377,45 @@ class Color3DLUT(MultibandFilter):
                          three color channels. Will be called ``size**3``
                          times with values from 0.0 to 1.0 and should return
                          a tuple with ``channels`` elements.
-        :param channels: Passed to the constructor.
+        :param channels: The number of channels which should return callback.
         :param target_mode: Passed to the constructor.
         """
         size1D, size2D, size3D = cls._check_size(size)
-        table = []
+        if channels not in (3, 4):
+            raise ValueError("Only 3 or 4 output channels are supported")
+
+        table = [0] * (size1D * size2D * size3D * channels)
+        idx_out = 0
         for b in range(size3D):
             for g in range(size2D):
                 for r in range(size1D):
-                    table.append(callback(
-                        r / float(size1D-1),
-                        g / float(size2D-1),
-                        b / float(size3D-1)))
+                    table[idx_out:idx_out + channels] = callback(
+                        r / (size1D-1), g / (size2D-1), b / (size3D-1))
+                    idx_out += channels
 
-        return cls((size1D, size2D, size3D), table, channels, target_mode)
+        return cls((size1D, size2D, size3D), table, channels=channels,
+                   target_mode=target_mode, _copy_table=False)
+
+    def alter(self, callback, channels=None, target_mode=None):
+        if channels not in (None, 3, 4):
+            raise ValueError("Only 3 or 4 output channels are supported")
+        ch_in = self.channels
+        ch_out = channels or ch_in
+
+        table = [0] * (self.size[0] * self.size[1] * self.size[2] * ch_out)
+        idx_in = 0
+        idx_out = 0
+        for b in range(self.size[2]):
+            for g in range(self.size[1]):
+                for r in range(self.size[0]):
+                    values = callback(*self.table[idx_in:idx_in + ch_in])
+                    table[idx_out:idx_out + ch_out] = values
+                    idx_in += ch_in
+                    idx_out += ch_out
+
+        return type(self)(self.size, table, channels=ch_out,
+                          target_mode=target_mode or self.mode,
+                          _copy_table=False)
 
     def filter(self, image):
         from . import Image