What’s it for? – Mask input node.
In this episode we are looking at Blenders Mask input node
while there are several ways to create masks in Blender this node is specific to Blenders mask function that can be found in both the Movie clip editor and the UV image editor. in order to use the node, first you need to create the mask. simply open the required editor and choose the mask option.
then simply select “New” and start drawing the mask on your image or movie frame by Holding down the Ctrl key and left clicking around the element you wish to mask.
once complete you can then switch to the compositor and add the mask node. press Shift A then select “input – Mask”. Open the mask you wish to use by selecting it from the drop down menu within the node itself. you can have several masks to choose from so be sure to name them appropriately. the mask node can the be connected to the node tree. usually this would be to the fac value of a mix node or an Alpha over in order to combine two or more images or render layers, though it can be used in any fac value socket should you simply need to have control over an area of an image. for example you could plug it into the value socket of a math node and use it to define an area of an image such as a sky element that you might wish to adjust
Checking the anti aliasing tick box can help to smooth out harsh edges and ticking the Feather check box. the scene size button gives you the option of changing the size of the mask from the scale of the scene to a fixed dimension. this is useful if you are masking an image that is different to the dimensions of the scene itself.
the motion blur check box allows you to match the blur of the mask to any movement of the scene. useful if your trying to mask a fast moving movie clip for example