Bluescreen technology

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Tom41
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Bluescreen technology

Post by Tom41 »

Anyone happen to know how the bluescreen chromakey unit was actually set up in KM? On most sets I've seen, whatever is blue above a certain threshold value is replaced with the background. Things that are near the threshold value (e.g. if someone's wearing a blue shirt), seem to flicker and sparkle - occasionally bits are background, other times they're foreground.
A good example in KM is in close-up of the tavern maid (series 5 I think). The background of her hairline is blue.

But in KM, it seems that the shadows from people and objects were able to be put on top of the background layer! Even shadows could be cast from blue objects (that should be overwritten with the background)

Or was the picture processed and the shadows added on digitally?

Finally, take a look at this image (external images not allowed, so it's a link)
Click here
It's a frame from the AVAUNT spellcasting sequence, where they kill a ghost with it. At one point, the screen's almost totally whited out - but look! You can see the blue table, and the blue steps/banister in the room where the dungeoneer was! Plus, the staircase seems to be casting its own shadow.

What you're seeing there is effectively the layout of the blue room, but with the blue replaced with white. Perhaps this is part of the electronic 'mask' they use for chromakey overlaying.

Edit: You can also see this effect (layout of the room) by freeze-framing a tape on a bomb room explosion, or when the blades come near to the camera in a Corridor of Blades scene.
Last edited by Tom41 on 07 Jul 2004, 20:32, edited 1 time in total.
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Forester
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Re:Bluescreen technology

Post by Forester »

Under standard chromakey you generate a greyscale matte. Anything that is white is background, anything that is black is foreground. Anything that is grey is a mix between the two.

But... There are more advanced systems which can detect the amount of luminance of the blue screen thus detecting shadows. It will then hold the luminance of that part and apply the background thus getting a shadow on the background. The methods used for determining what is and isn't blue are variable. Some systems can even combine a show of the blue screen without foreground objects on it to assist in determining what is and isn't meant to be background. These can become so sophisticated as to even pick out people's strands of hair correctly.

At the end of the day it's down to the technology employed as to what the result is with a blue screen. Old school methods say to light the blue screen evenly to ensure there are no shadows. Newer methods allow the use of shadows. What method was used for Knightmare I can not say.
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NeilJones
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Re:Bluescreen technology

Post by NeilJones »

Tom41 wrote: Anyone happen to know how the bluescreen chromakey unit was actually set up in KM? On most sets I've seen, whatever is blue above a certain threshold value is replaced with the background. Things that are near the threshold value (e.g. if someone's wearing a blue shirt), seem to flicker and sparkle - occasionally bits are background, other times they're foreground.
This will depend on how tolerant and how advanced the equipment is, as well as how you set it up. I mean if you specify an exact shade of blue to replace with something else (weather forecasting style) then the whole concept buggers itself up when you cast a shadow because then it will be a different shade of blue. Whereas with a more tolerant setup the system is intelligent enough to know this and make allowances.
But in KM, it seems that the shadows from people and objects were able to be put on top of the background layer! Even shadows could be cast from blue objects (that should be overwritten with the background)
Not necessarily. Think weather forecasts again, the most obvious example of bluescreen technology if ever I saw one. The blue (or whatever colour) is behind the presenter. He will create a shadow naturally when he sticks his arm out to point at his map assuming the light is illuminating him from the front. The advanced nature of this technology means that that shadow can be eliminated. Previous incarnations would just replace everything that was blue or whatever; shadows aren't "seen" so it looks like they're on top when the blue is taken out.

With regards to blue objects, I dare say one could set up exceptions to the general rule. In the early days of this technology on the weather forecasts the presenters were not to wear the same colour as the back screen as it would look as if there were wearing the map! These days everything's automated and the system can be told to ignore areas (such as eye colour) when doing the replacing of the blue.
Finally, take a look at this image (external images not allowed, so it's a link)
Click here
It's a frame from the AVAUNT spellcasting sequence, where they kill a ghost with it. At one point, the screen's almost totally whited out - but look! You can see the blue table, and the blue steps/banister in the room where the dungeoneer was! Plus, the staircase seems to be casting its own shadow.
Studio lighting. Limitation of the way things have to be done to get something else don't. Will probably be a computer effect tacked on top but you can't cut the studio lights as it would then look indecidably odd of a white flash and a dark area. As I say, later technology adressed this to sort out these overhanging bits like shadows and what not.
What you're seeing there is effectively the layout of the blue room, but with the blue replaced with white. Perhaps this is part of the electronic 'mask' they use for chromakey overlaying.
The the chromakey backdrop (assuming we're using blue as the master) can, in theory, be replaced with any other colour or image as required. With the technology available here, it's a bit rough around the edges but then having said that you're noo supposed to be looking at it in this way anyway through a freeze frame! :D
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spacehog
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Re:Bluescreen technology

Post by spacehog »

The set-up was as follows. There were two identical bluescreen rooms, each with three walls and no ceiling. They were built adjacent to each other in the center of Angila TV's large Studio E on Magdalen Street in Norwich. The area for the helpers was set up in the corner of the same studio.

Mostly, the right-hand blue room was used for superimposing the dungeoneer onto the background, while the left-hand room was used for live close-ups of hand-operated puppets such as the dragon's head, and the flying dragon.

The right-hand room used a luminescence-sensitive chromakey system, so live shadows which were cast affected the brightness of the superimposed dungeon graphics. The room was reasonably consistently lit; any variations in brightness of the walls was transferred to the graphics, but this didn't usually matter as it was quite subtle and the shape of the real/virtual rooms typically matched up anyway.
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Re:Bluescreen technology

Post by Malefact »

Some exhaustive, if not definitive, information here. Thanks to all involved - it's a fascinating read.

Welcome to the forum, btw, spacehog. You're obviously very much in the know about what exactly went on when the series were being made. I'm guessing that you were involved in some way. How so, please? I'm very curious. :)
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Illusion
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Re:Bluescreen technology

Post by Illusion »

Interesting. I think I'll add that bit of inside info to the site :)
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spacehog
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Re:Bluescreen technology

Post by spacehog »

You guess right - I worked for Anglia TV for a bit which involved a few days doing menial tasks on the Knightmare set during pre-production. There was a surreal Sunday when I was alone on that set all day, babysitting a computer doing some rendering. Very strange to wander around when it's all quiet!

Incidentally I also worked for Televirtual for a while, editing motion capture data.
Malefact
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Re:Bluescreen technology

Post by Malefact »

Ah, I see! I'm not surprised that you say that you've worked for Televirtual - beveryafraid said once that he likes to work with tried and trusted talent (hence Tom Karol hosting the TimeGate pilot).
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spacehog
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Re:Bluescreen technology

Post by spacehog »

Illusion - while you're adding stuff to the site, just noticed this (for comprehensiveness's sake!):

The lady in the photo in the smirkenorff section whom you have captioned "stage manager (we think)" is in fact Claire Whittenbury, Assitant Producer of Knightmare.
Illusion
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Re:Bluescreen technology

Post by Illusion »

Thanks. Will note that.
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Tooley
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chromakey

Post by Tooley »

I'm working on a project using chromakey. I was told there is software available for the keying process. I've searched for this, with no luck. Can anyone help me?

This is for a small project. Not much in the way of a budget, however we already have the paint and cameras
Snowcat
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Re:chromakey

Post by Snowcat »

I don't know whether you have access to these but programs such as Adobe Premier, Adobe After Effects and Vegas Video all have features/ Plugins avaliable for doing Chromakey work.
(All of these are avaliable via the 'Long John Silver' method but I'll leave the specifics for yourself to find... ;) )

If all else fails, try having a look around some of the download sites and places like 'PC Format'. They occasionally have utilities that could do these kind of things for you.

Hope that Helps! :)
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NYGuy322
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Re:chromakey

Post by NYGuy322 »

How much would things like this cost to buy?
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