Nuke Toolkit | Green Screen Compositing [Lesson 3 & 4]

Lesson four was essentially a recap of lesson three, going back over tools and nodes; 'rescoping', 'transform', 'colour node', 'reformat' and introducing a few others; 'pre-multiply', 'noise', 'primate', 'premult' and 'backdrop'. 

We walked through a tutorial wherein we used the program to separate and move selected parts of an image (i.e. a door sliding open), that best illustrated the effects of these tools and nodes. After changing the gamma values to make the viewport lighter for ease of sight, we proceeded to use the 'rotoscope' tool to cut round the edges of the door, (and then specifically down the centre to separate it into two further pieces).  To go about animating the doors, we needed the pieces to move realistically along the door frame. To do this we used another rotoscope node, that imitated the lines of the door, to best judge the perspective and ultimately the vanishing point. Here we move the pivot to this point, and use the 'transform' node's scale option to move the doors in specifically to the newly positioned pivot point. 

We animate the doors to open further along the timeline. Once open the second image is revealed (as a long hallway leading back further). The position and colour is wrong though. To fix this we imported both 'transform' and 'reformat' node to move the background down, and then the 'grade' node to match its colour to the foreground.

Beyond this we would edit the final file (video footage of a character walking), provided so the figure would appear to step through the doors as they part. Initially we used the 'primatte' node to help clear away any unnecessary content. This is particularly useful for adjusting any markers, and/or uneven lighting evident on the green screen, so they're invisible in the final composited film. 'Primatte' typically samples the pixels of the specific eye-dropped area, to help it distinguish between two or more areas (i.e. the background and the foreground). This allows the program to 'clean-up' both ,or either. This can be done using the 'smart select BG Color' that uses a histogram to help separate them for accurately, and/or operations such as 'clean BC Noise' that helps remove elements of 'noise' from the image or video. It's sometimes easier to change the viewport to the alpha channel, to better distinguish the two.

This was as far as we got yesterday, but it ultimately covers all the relevant tools in question. It might be worth returning to, especially if my final bestiary requires compositing 3D and 2D drawn elements from multiple files.