Add common blend mode functions

Author: jepler

adafruit_pycamera/imageprocessing.py

@@ -82,3 +82,123 @@ def emboss_greyscale(bitmap, mask=None):
 def ironbow(bitmap, mask=None):
     """Convert an image to false color using the 'ironbow palette'"""
     return bitmapfilter.false_color(bitmap, ironbow_palette, mask=mask)
+
+
+# pylint: disable=invalid-name
+def alphablend_func_factory(frac, nfrac=None):
+    """Create an alpha-blending function for a specific fractional value
+
+    The resulting function can be used with ``bitmapfilter.blend`` and
+    ``bitmapfilter.blend_precompute``.
+    """
+    if nfrac is None:
+        nfrac = 1 - frac
+
+    def inner(a, b):
+        return frac * a + nfrac * b
+
+    return inner
+
+
+def screen_func(a, b):
+    """The 'screen' blend mode.
+
+    This function can be used with ``bitmapfilter.blend`` and
+    ``bitmapfilter.blend_precompute``."""
+    return 1 - (1 - a) * (1 - b)
+
+
+def overlay_func(a, b):
+    """The 'overlay' blend mode.
+
+    This function can be used with ``bitmapfilter.blend`` and
+    ``bitmapfilter.blend_precompute``."""
+    return 2 * a * b if a < 0.5 else 1 - 2 * (1 - a) * (1 - b)
+
+
+def hard_light_func(a, b):
+    """The 'hard light' blend mode.
+
+    This function can be used with ``bitmapfilter.blend`` and
+    ``bitmapfilter.blend_precompute``."""
+    return 2 * a * b if b < 0.5 else 1 - 2 * (1 - a) * (1 - b)
+
+
+# illusions.hu formula version
+def soft_light_func(a, b):
+    """The 'soft light' blend mode.
+
+    There are various soft light blend functions. The "illusions.hu" variant of
+    soft light is used.
+
+    This function can be used with ``bitmapfilter.blend`` and
+    ``bitmapfilter.blend_precompute``."""
+    return a ** (2 ** (2 * 0.5 - b))
+
+
+def color_dodge_func(a, b):
+    """The 'color dodge' blend mode.
+
+    This function can be used with ``bitmapfilter.blend`` and
+    ``bitmapfilter.blend_precompute``."""
+    return a / (1 - b) if b != 1 else 1
+
+
+def linear_dodge_func(a, b):
+    """The 'linear dodge' blend mode.
+
+    This function can be used with ``bitmapfilter.blend`` and
+    ``bitmapfilter.blend_precompute``."""
+    return a + b
+
+
+def divide_func(a, b):
+    """The 'divide' blend mode.
+
+    This function can be used with ``bitmapfilter.blend`` and
+    ``bitmapfilter.blend_precompute``."""
+    return a / b if b else 1
+
+
+def multiply_func(a, b):
+    """The 'multiply' blend mode.
+
+    This function can be used with ``bitmapfilter.blend`` and
+    ``bitmapfilter.blend_precompute``."""
+    return a * b
+
+
+def subtract_func(a, b):
+    """The 'subtract' blend mode.
+
+    This function can be used with ``bitmapfilter.blend`` and
+    ``bitmapfilter.blend_precompute``."""
+    return a - b
+
+
+def color_burn_func(a, b):
+    """The 'color burn' blend mode.
+
+    This function can be used with ``bitmapfilter.blend`` and
+    ``bitmapfilter.blend_precompute``."""
+    return a * (1 - b)
+
+
+def linear_burn_func(a, b):
+    """The 'linear burn' blend mode.
+
+    This function can be used with ``bitmapfilter.blend`` and
+    ``bitmapfilter.blend_precompute``."""
+    return a + b - 1
+
+
+darken_only_func = min
+"""The 'darken only' blend mode.
+
+This function can be used with ``bitmapfilter.blend`` and
+``bitmapfilter.blend_precompute``."""
+lighten_only_func = max
+"""The 'screen' blend mode.
+
+This function can be used with ``bitmapfilter.blend`` and
+``bitmapfilter.blend_precompute``."""