Monday, 14 December 2009

Playing with the Chroma Key Video Technique

I watched Kevin McLaughlin at the Teach meet /Ed Tech round up do a demonstration of green screen video work on an Apple laptop. To see the clip visit , it is on the 7th video of the set.

Blue screen, chroma-key or green screen is something I have often wondered about and always meant to investigate but just never got round to. It is very easy on the Apple, one has to go into the Advanced settings on iMovie and select Chroma-Key /Green screen or something similar! I promptly tweeted that I wanted an Apple to experiment with when James Ashton tweeted back that I could do it with a PC and he would write a blog giving instruction. Amazingly he then apologised for it taking so long – the instructions were in place that same night :-) Many thanks to James!! I followed the instructions in his blog post instructions and downloaded the plug in needed. I thought I was all set up!

At work the following Monday I set up a blue screen on the Smartboard,  that seemed to be an easy answer for primary schools. Sadly the royal blue was washed out by the projector light, so was I! That was a non-starter. Fail number one!

Next I covered a board with royal blue poster paper, that seemed perfect. I asked a colleague to record me with a Flip cam. My idea was that I would introduce my avatar and stand by her in Second Life. I did my bit of speech and took the camera back, I had instructed my colleague not to go off the blue paper with the recording but those instructions were not enough, he videoed me close up so that there was no room left to superimpose me on anything else, it was all my head and shoulders with a bit of blue around the edges. Failed a second time.

I took the blue poster paper home and stuck it along wardrobes before asking my husband to record me. This felt like a sure winner, was so sure it would work I dug out an old digital camcorder as it is a much better resolution than the Flip Cam. Fail number three – I have no firewire port to download it from DV tape any more :-(

So now I am waiting / working at home waiting for the TV Aerial man to come and fix the aerial before Christmas. Dare I ask him to accompany me to the bedroom to video me once again using the Flip Cam? Not sure even I am that brave! So on hold again.

This must be the only blog post ever that is being written over weeks!
During the time span between all these failures – over a week now – I have been wondering about how I would use it in class.

First thoughts -
• documentaries – children reporting findings from around the world in a geography project being set against film from that country,
• maybe story telling where their story is set in a forest, retelling the story of Jonah and the Whale against a crashing sea, but it would take a lot of work to film the background scenes for the story unless they were stock footage
• making adverts – setting themselves in a dream house of on a desert island but again it would depend on the stock footage available
• children reporting on news items with video in the background – especially good if they could use the real footage from the BBC news and project themselves as newscasters
• in all cases a single picture could be used as the background but I not sure whether that is an advantage or just a difficult way of doing it, I would need to work with children to establish that.

I am definitely lacking imagination this morning, I can’t think of any more.

I am beginning to think that for primary school Chroma Key may be a non-starter taking too much work for too little result but for secondary pupils I guess it would be a very different story, especially for those pupils doing media exam work.

So – back to the Flip cam, my son took footage of real life me, I exported it exported from Flip, tried to import into Windows Movie Maker – oh dear Data Execution Prevention kicked in. The program closed, I read the details, learned that I can switch DEP off, tried - but -  WMM can’t run without it. Eventually I put the clip onto external hard drive, took to another computer with licence for a video convertor…. This is getting silly!

In the meantime I have taken footage of my avatar in Second Life using Fraps. Even that did not go as smoothly as I expected, control Alt-Ctrl & F1 which usually switches off the user interface refused to play… but we all know there is more than one way to skin a cat!

I think finally I have two videos, one of my avatar in Second Life and one of me against a blue screen in real life. Can I merge the two?

I think at that point I should stop listing problems, but the conculusion of another three hours of downloading codecs, updating codecs and trying out various formats left me with a pretty poor video clip where my real self left a faded out avatar, there was nothing like enough light in the room to enable the blending of the images properly.  Still I experienced  a huge sense of achievement. I really don't like techie stuff getting the better of me but not at all convinced this is for the average primary school :-)


Anonymous said...

Hiya Carol!, thought i'd post on here too, ur problem lies witht the colour blue u are using, when using rehanFX did u try all the diff varieties of blue chroma? 0.1 0.2 0.3 etc, i used to have the same problem when the blue didn;t quite match up to the chroma, it made the image show through only just,

remember the additional steps you went through, such as converters, only depend on the camera you use, and the codecs are a once install. they'll lie forever on ur pc.

lol! thats why we teachers prepare for the lessons :P there is also a very video converter i use alot i'll email u the address :)

Carolrb said...

Thanks James. I have remade it using a better transition. Just going to upload it to BlipTV now.

Not sure I would want to take this on with children with a PC though, unless it was one in a classroom and set up ready, then it may work!

I know that one of our schools has a media suite, a room full of Apples, I would try it there though :-)