Python API: add template for image processing

Since a few releases it is possible to process Blenders images much
more effficiently than before thanks to the `foreach_get`/`foreach_set`
methods. This new template shows how those methods can be used together
with numpy.

Differential Revision: https://developer.blender.org/D9400

release/scripts/templates_py/image_processing.py

@@ -0,0 +1,35 @@
+# This sample shows the an efficient way of doing image processing
+# over Blender's images using Python.
+
+import bpy
+import numpy as np
+
+
+input_image_name = "Image"
+output_image_name = "NewImage"
+
+# Retrieve input image.
+input_image = bpy.data.images[input_image_name]
+w, h = input_image.size
+
+# Allocate a numpy array to manipulate pixel data.
+pixel_data = np.zeros((w, h, 4), 'f')
+
+# Fast copy of pixel data from bpy.data to numpy array.
+input_image.pixels.foreach_get(pixel_data.ravel())
+
+# Do whatever image processing you want using numpy here:
+# Example 1: Inverse red green and blue channels.
+pixel_data[:,:,:3] = 1.0 - pixel_data[:,:,:3]
+# Example 2: Change gamma on the red channel.
+pixel_data[:,:,0] = np.power(pixel_data[:,:,0], 1.5)
+
+# Create output image.
+if output_image_name in bpy.data.images:
+    output_image = bpy.data.images[output_image_name]
+else:
+    output_image = bpy.data.images.new(output_image_name, width=w, height=h)
+
+# Copy of pixel data from numpy array back to the output image.
+output_image.pixels.foreach_set(pixel_data.ravel())
+output_image.update()