Add blend examples

this includes most of the blend functions listed on the related wikipedia
article, though only a few are tested.

Author: jepler

adafruit_pycamera/imageprocessing.py

@@ -85,7 +85,7 @@ def ironbow(bitmap, mask=None):
 
 
 # pylint: disable=invalid-name
-def alphablend_func_factory(frac, nfrac=None):
+def alphablend_maker(frac, nfrac=None):
     """Create an alpha-blending function for a specific fractional value
 
     The resulting function can be used with ``bitmapfilter.blend`` and

examples/filter/code.py

@@ -21,7 +21,95 @@
 from adafruit_pycamera import imageprocessing
 from adafruit_pycamera import PyCameraBase
 
+
+blend_50_50 = bitmapfilter.blend_precompute(imageprocessing.alphablend_maker(0.5))
+screen = bitmapfilter.blend_precompute(imageprocessing.screen_func)
+overlay = bitmapfilter.blend_precompute(imageprocessing.overlay_func)
+hard_light = bitmapfilter.blend_precompute(imageprocessing.hard_light_func)
+soft_light = bitmapfilter.blend_precompute(imageprocessing.soft_light_func)
+color_dodge = bitmapfilter.blend_precompute(imageprocessing.color_dodge_func)
+# linear_dodge = bitmapfilter.blend_precompute(imageprocessing.linear_dodge_func)
+# divide = bitmapfilter.blend_precompute(imageprocessing.divide_func)
+multiply = bitmapfilter.blend_precompute(imageprocessing.multiply_func)
+# subtract = bitmapfilter.blend_precompute(imageprocessing.subtract_func)
+# color_burn = bitmapfilter.blend_precompute(imageprocessing.color_burn_func)
+# linear_burn = bitmapfilter.blend_precompute(imageprocessing.linear_burn_func)
+# darken_only = bitmapfilter.blend_precompute(min)
+# lighten_only = bitmapfilter.blend_precompute(max)
+
+
+def blender(f):
+    def inner(b):
+        return bitmapfilter.blend(b, b, testpattern, f)
+
+    return inner
+
+
+def reverse_blender(f):
+    def inner(b):
+        return bitmapfilter.blend(b, testpattern, b, f)
+
+    return inner
+
+
+inverse_greyscale_weights = bitmapfilter.ChannelMixer(
+    1 - 0.299,
+    1 - 0.587,
+    1 - 0.114,
+    1 - 0.299,
+    1 - 0.587,
+    1 - 0.114,
+    1 - 0.299,
+    1 - 0.587,
+    1 - 0.114,
+)
+
+blur_more = [
+    4,
+    15,
+    24,
+    15,
+    4,
+    15,
+    61,
+    97,
+    61,
+    15,
+    24,
+    97,
+    154,
+    97,
+    24,
+    15,
+    61,
+    97,
+    61,
+    15,
+    4,
+    15,
+    24,
+    15,
+    4,
+]
+
+
+# "Sketch" filter based on
+# https://www.freecodecamp.org/news/sketchify-turn-any-image-into-a-pencil-sketch-with-10-lines-of-code-cf67fa4f68ce/
+def sketch(b):
+    bitmapfilter.mix(b, inverse_greyscale_weights)
+    memoryview(auxbuffer)[:] = memoryview(b)
+    bitmapfilter.morph(auxbuffer, blur_more)
+    bitmapfilter.blend(b, auxbuffer, b, color_dodge)
+    bitmapfilter.mix(b, inverse_greyscale_weights)  # get rid of magenta halos
+    return b
+
+
 effects = [
+    ("sketch", sketch),
+    ("50/50", blender(blend_50_50)),
+    ("multiply", blender(multiply)),
+    ("soft light", blender(soft_light)),
+    ("hard_light", blender(hard_light)),
     ("blue cast", imageprocessing.blue_cast),
     ("blur", imageprocessing.blur),
     ("bright", lambda b: bitmapfilter.mix(b, bitmapfilter.ChannelScale(2.0, 2.0, 2.0))),
@@ -65,6 +153,9 @@ def cycle(seq):
 pycam = PyCameraBase()
 pycam.init_display()
 
+testpattern = displayio.Bitmap(208, 208, 65535)
+auxbuffer = displayio.Bitmap(208, 208, 65535)
+
 
 def main():
     filename = "/cornell_box_208x208.jpg"
@@ -74,6 +165,9 @@ def main():
     decoder.open(filename)
     decoder.decode(bitmap0)
 
+    decoder.open("/testpattern_208x208.jpg")
+    decoder.decode(testpattern)
+
     label = Label(font=FONT, x=0, y=8)
     pycam.display.root_group = label
     pycam.display.refresh()

examples/filter/testpattern_208x208.jpg

@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: 2023 Jeff Epler for Adafruit Industries
+
+SPDX-License-Identifier: Unlicense