Apple MA434Z/A User Manual - Page 536

Note: If you had simply connected the car_mask image to the M input of the Pan node, rather than using the KeyMix method, you would have masked normally concatenating nodes and broken the concatenation between the CornerPin and Pan functions. Using Images Without an Alpha Channel A masked image does not need an alpha channel. Connecting an image without an alpha channel as the mask doesn't immediately have an effect, however, since by default mask inputs are expecting an alpha channel. To fix this, switch the mask channel to R, G, or B in the Mask subtree to select a different channel to use as a mask. To use the luminance of the image, apply a LumaKey node to your mask image and leave the channel at A, or apply a Monochrome node and select R, G, or B. Masking Layers Another form of masking involves using an image as a holdout matte to cut holes in another image. Masking layers requires a different approach, since you should never mask a layer using the side input. Typical nodes used for this task are Inside and Outside. The Inside node puts the first image in only the white areas of the second image's alpha, and the Outside node puts the first image in only the black areas of the second image's alpha. The following example continues with the result node tree from the above example. Since the sign is further in the foreground of the scene, you do not want the sign to get the brightening effect. Use the Outside node to put the light mask outside of the sign mask, in effect punching a hole in the light mask with the sign mask. Using the Outside node to isolate the sign: 1 In the Node View, select KeyMix2 and apply a Layer-Outside. 2 Double-click the Outside node to load it in the Viewer. 536 Chapter 19 Using Masks