Function: masked_blend

--Usage--
> masked_blend(light: image, dark: image, mask: image)

Blend two images together using a third as a mask.
On pixels the mask is white the 'light' image is used, where the mask is black the 'dark' image is used.
For grey pixels the images are blended.

The images must have the same size.

--Parameters--
! Parameter	Type			Description
| @light@	[[type:image]]		Image for the light colores in the mask
| @dark@	[[type:image]]		Image for the dark colores in the mask
| @mask@	[[type:image]]		Mask image that selects between the two images

--Examples--
> masked_blend(light: "image1.png", dark: "image2.png", mask: "image3.png")  ==  [[Image]]
>>> masked_blend(light: <img src="image1.png" alt='"image1.png"' style="border:1px solid black;vertical-align:middle;margin:1px;" />, dark: <img src="image2.png" alt='"image2.png"' style="border:1px solid black;vertical-align:middle;margin:1px;" />, mask: <img src="image3.png" alt='"image3.png"' style="border:1px solid black;vertical-align:middle;margin:1px;" />) == <img src="image_masked_blend.png" alt='"image_masked_blend.png"' style="border:1px solid black;vertical-align:middle;margin:1px;" />

--See also--
| [[fun:linear_blend]]		Blend two images together using a linear gradient.
| [[fun:combine_blend]]		Blend two images together using a given [[type:combine|combining mode]].
