Making of Intergrated Practice: Week 3: 9/10/18: After Effects Workshop pt2 Greenscreening/ Alpha channels.

In week 3 of Making of Integrated Practice, our workshop in After Effects was focused on the use of green screening and our introduction to Alpha channels.


James, the technician had provided us with assets to use for the exercise, one of them was a TIFF sequence of a woman explaining and some background ideas. the sequence was imported from the first photo and made into footage after being imported to after effects. The application of the green screen method wasn't too different from Premier pro as this too used Key light  keying which was found in effects and presets. James directed our attention to the issues when doing green screening and one of them was called spilling. This was when some of the green screen was reflected on the presenter and would be affected when the green screening process was applied. Another issue we learned about was in the motion blur present in the footage.


Annabeth our tutor reminded us about the colour theory session we did in our first year and how colours complement each other. This applied to green screening, for example the presenter was wearing a yellow shirt which didn't complement the green screen as yellow was a colour used to make green. I felt this made sense and was something to consider when doing green screening with 2D animation for our projects.

James showed us a trick of adjusting the noise left behind when the keying was applied and that was when we switched the channels from RGB to Alpha which showed a white and black background. In the keying we could adjust the white and black with the clip black and clip white adjustments. In working with this I learned that when the presenter was fully white and the black background reduced of noise I discovered when changing the channel back to RGB that the presenter seemed more presentable in appearance.


One element I learned of interest was how James said that footage that we import into After Effects don't have the same time scales, such as the footage imported was 25fps when imported it was 30fps. We were shown how to correct this by right clicking the footage selecting interpret footage and main which brought up what would be the footage properties from there we could alter the FPS option, which in this case James asked us to set to 29.97fps.

What I found interesting was the use of the pen tool in the footage which allowed us to create a mask to follow the presenter as it moves. The way this worked was while we had the greenscreen footage selected and use the pen tool to create the mask. When playing the footage the mask had to be adjusted using key frames and edit the anchor points to make room for any moving limbs or if the character was walking along. This I felt was rather simple.

I found this lesson to be rather difficult as it was hard to understand some of the steps needed to refine the green screen and even the layering of the same footage using the alpha channels. Whilst helpful in refining the presentation of the footage did seem hard to capture. However as we were presented with a terrible example of greenscreen footage I was able to translate what we learned from the first example into the footage.


However I found the masking process hard as I didn't memorise every detail but with some calm thinking I felt I found the task easier to perform. One thing I found difficult was making sure the green was present on the footage even if it meant cutting off the presenters head. However James told me to try and avoid scaling as it could generate pixels and a less presentable outcome. Though an asset that James provided us with wasn't available I made do with a comic book BAM! logo for the effect.

We were then shown the export settings for alpha footage and how different export settings such as quicktime would have more or fewer options. One option was RGB & Alpha which was the required setting for batching footage like the sample we used. We could even export it through Adobe Media Encoder which I learned in first year when the H.264 codec option was removed in updating the After effects program.


I found todays session most insightful on the greenscreening in After effects and how it was not too different from Premier Pro but with a few more adjustments. I also learned some helpful processing power advice to close after effects while the media encoder processes the animation. I feel this session was hard to make sense of but ultimately it did provide some insight into how film editors bring green screen footage together. In hindsight I could've asked for more help in understanding the process of the Alpha channel and the keying options from James when working with the terrible green screen example. This could be something I remember for future reference.


In conclusion todays workshop was hard but insightful at the same time, and I may experiment with this greenscreen further in either 2D work or any green screen work we do in the future be it on the shared module or the other modules on the course.


In future I shall ask for a second opinion on the alpha channel and isolating the presenters in the green screen footage.