Blog Post 60 - Stage 3 - Adobe Premiere - Green Screening

Scenary Background Video Clip

As previously mentioned in the last blog post in regards to video effects, one particular video element that I took a detailed look into was that of the technique of green screening. Although this was not something that was required for this assignment to satisfy the minimum requirements of the specification, this particular technique is something that was definitely worth while looking into in relation to the advanced features that go above and beyond the original specification that had been set out. At this point in time, I feel that it is worth pointing out that the name of "green screening" is one that that has been adapted over time due to the generic use of a green (or even sometimes blue) screen, however the true name for this technique is that of Chroma Keying.

Green Screen Removed

In simple terms the use of Chroma Keying and/or Green Screening is that of placing two different pieces of video together, which in hindsight is in a similar fashion to that of layering in Adobe Photoshop and Adobe Illustrator. However there is more complications in regards to this in Premiere and the use of video clips obviously due to the nature of the clips not behind static and them constantly moving. Although the name green screen is given to this particular technique, in theory any colour can be used as the "green screen", however as time goes by the use of a green coloured screen is one that is used due green being the least common colour worn by people. Arguably as long as the colour used it solid and one shade then the software in Premiere will be able to decipher this from the subject that you want to keep, however this must be of a significant contrast to that of the subject. For example a person speaking might be wearing black coloured clothes and therefore the background screen colour would ideally be that of white, and not of dark grey or black as it would be very difficult to decipher the difference and therefore result in a less than satisfactory end result and appearance to that of the Chroma Keying effect.

Brought together

The basic key procedure to going about the Chroma Keying effect is that you firstly need a suitable video clip that will act as the background that you are wishing to to merge your next clip, which is in regards to the piece of footage that will be filmed in front of the green screen. For this particular blog post write-up and explanation the background source clip that will be used is that of a mountain countryside scene. Once this has been imported into Premiere in the usual fashion is then it can be placed on the timeline however due to the layering involved this should be placed in the Video 2 timeline slot. By doing this, this leaves room of the green screened footage to be placed in the Video 1 timeline slot as to enable there to be the layered effect as to have the background in place and then the green screened footage over the top of this. Next the green screen footage could then be imported into the Premiere project and added to the timeline in the Video 1 timeslot as previously mentioned. Once that was done, by navigating to the Keying folder in Video Effects I was able to find the effect called Ultra Key which would allow me to remove the green background from that of the footage. 

To do this, though, the next stage was to set the key colour for the Ultra Key. By using the eye dropper tool this enabled me to select the green colour of the background and once this was done then this meant that the background turned black. This, however, wasn't really the case as by turning black in colour this meant that the background around the subject was in fact transparent (harking back to the times of using Adobe Photoshop and Adobe Premiere). Once this was done this posed the issue of the two clips being of a different size and resolution and therefore there was some resizing needing to be done which was rather simple - double clicking on the clip in the viewing area this meant that when also holding down the shift key the aspect ratio was kept the same and the video clips dimensions were not skewed. I decided to resize the clip as this was to ensure that the end result was as realistic as possible - for example there end result would not appear very professional if the scaling did not realistic with the subject of green screening appearing either too tall or too short. 

Eight Point Garbage Matte

Another element of Premiere that I also looked into in regards to the green screening element was that of a Garbage Matte, and in particular that of an Eight Point Garbage Matte. These is a really useful element of Premiere that is included specifically with that of the green screening and Chroma Keying in mind. The use of the Garbage Matte is particularly useful when the video clip that you are using for the green screen isn't exactly perfect and some edges might show. With this in mind, the green screen footage that I was using above was nearly perfect, however on the odd occasion it was apparent that some white coloured wall outside of the green screen area was showing through, and obviously had not been picked up by the green colour selected as the Key colour before. By making use of the Garbage Matte this meant that I was about to adjust the size of the edges of the green screen subject footage - the clue in regards to the number of points that you can edit and change is in the name of Eight Point Garbage Matte, however there are three types of Mattes available ranging from 4, to 8 and then to 16 point.

Having made use of the garbage matte to slightly bring the corners of the green screen footage in this meant that I was happy with the end effect of the two clips being brought together. There were further options available to tweak the appearance which include some examples like Smoothing which could be increased to gently smooth the edges of the subject of the green screen. Personally I think that this is a worthwhile option to tweak and increase as by just gently increasing the amount of smoothing this meant that a more realistic end result was produced with the edges appearing more natural and less jagged which they previously appeared. 

Now that I had looked at the technique of green screening at the end of this I felt much more confident in how this works and if needed this could be something that I may use when I am at the stage of compiling my promotional video. At this moment in time I am not too sure whether or not I would use this however it is certainly a technique to bear in mind. In regards to the next stage and now that I have looked into a vast range of difference techniques and elements that are on offer in Premiere I feel that I can now move onto the design phase of the promotional video.