Camera Projection - Nuke 101: Professional Compositing and Visual Effects - page 469

Figure 11.19. Turning off the Rgba.alpha channel in the Properties panel.
6. Align your brush using the lines on the building. Because there's perspective
changethroughouttheheightofthebuilding,you'llhavetochangethealignment
as you go up and down the building. Start painting ( FIGURE 11.20 ).
Figure 11.20. Using the window edges to align the clone brush.