Homemade substitute for a "blue screen" when chromakeying?

Jan 6, 2007 at 3:43pm

Homemade substitute for a "blue screen" when chromakeying?

Hi all,

Has anyone any suggestions on how to get a good background for chromakeying at home?

My patch works fine, it’s essentially Jitter tutorial 10 with a few tweaks, but i just can’t get the backdrop right.

I’ve almost got there with a uniformly painted wall, but it’s not quite enough…i have to mess with the tolerance to the point where i’m getting some artifacts on the subject, as opposed to just the background.

I don’t have much money to spend on it and ideally i’d like it to be as portable as possible, so maybe a sheet of fabric to hang on a wall or something similar?

Maybe a halogen light placed behind the subject, illuminating the area to be chromakeyed onto?

What about a white sheet, washed using a washing powder with that “brillant white” affect, (that makes it glow under UV light), and a UV light to illuminate it?

The simpler and cheaper the better, but all suggestions and experiences are more than welcome.

Thanks in advance,
John

#29523
Jan 6, 2007 at 4:11pm

http://snipurl.com/nk4f
and many more like that in “the google”
after you build something like this (you said portable) the other key is to
use separate lighting for your talent and your green screen. this is
important for treating those “blue spills”
if your outside you can get nice blue screen using mother nature bluesky,
see “so watcha want” or that old RHCP vid (i cant remmebr the name)

On 1/6/07, john inder wrote:
>
>
> Hi all,
>
> Has anyone any suggestions on how to get a good background for
> chromakeying at home?
>
> My patch works fine, it’s essentially Jitter tutorial 10 with a few
> tweaks, but i just can’t get the backdrop right.
>
> I’ve almost got there with a uniformly painted wall, but it’s not quite
> enough…i have to mess with the tolerance to the point where i’m getting
> some artifacts on the subject, as opposed to just the background.
>
> I don’t have much money to spend on it and ideally i’d like it to be as
> portable as possible, so maybe a sheet of fabric to hang on a wall or
> something similar?
>
> Maybe a halogen light placed behind the subject, illuminating the area to
> be chromakeyed onto?
>
> What about a white sheet, washed using a washing powder with that
> “brillant white” affect, (that makes it glow under UV light), and a UV light
> to illuminate it?
>
> The simpler and cheaper the better, but all suggestions and experiences
> are more than welcome.
>
> Thanks in advance,
> John
> –
> Imagination is more important than knowledge – A. Einstein
>

#92470
Jan 6, 2007 at 4:14pm

at my school we had a green screen that used a super bright neonish color painted right on the wall and lights that pointed down from above at a 45 degree angle that evenly illuminated the wall. I think your only issue is that you need to make sure its all even color and illumination, also you will get color spill onto the back of the person or thing in front of it, so you will need to make some sort of post key green/blue reduction part into your patch. Im sure theres tons of websites that talk about this on the net, just google or wiki it.

NCRIII

#92471
Jan 6, 2007 at 4:59pm

Keep in mind that the video digitizer you are using also has a large
effect on how successful your KEY will be. For example, DV being in
4:2:0 color space, which has a limited (ie compressed) chroma
information, this makes it difficult to get accurate keys. Another
factor is 8bit vs 10bit color processing on the chips themselves.
Pro level keying happens with 4:4:4 uncompressed sampling and 10bit
(or higher) resolution. It is likely that your background is only a
piece of your problem, and you might have to live with some artifacts
if your doing it on the cheap with the video hardware.

– deKam

> at my school we had a green screen that used a super bright neonish
> color painted right on the wall and lights that pointed down from
> above at a 45 degree angle that evenly illuminated the wall. I
> think your only issue is that you need to make sure its all even
> color and illumination, also you will get color spill onto the back
> of the person or thing in front of it, so you will need to make
> some sort of post key green/blue reduction part into your patch.
> Im sure theres tons of websites that talk about this on the net,
> just google or wiki it.
>
> NCRIII

#92472
Jan 6, 2007 at 6:05pm

In my limited keying experience, it seems to be all about good lighting.
You can usually find big rolls of brightly colored paper at art
stores. Stay away from stuff that is too shiny.

Best of luck.

Andrew B.

#92473
Jan 8, 2007 at 8:22pm

Thanks for all your replys, in hindsight i can’t believe i didn’t just Google it first!

deKam, you make a good point about DV Cameras using compression. It’s something that didn’t occur to me which really should have.

I did actually get very close just using my bog-standard JVC camcorder, in an averagely lit room, but i was trying to use a yellow(ish) white(ish) painted wall. The problem was that the tint was just a little too close to the skin colour of the subject, i could actually see that it could be a problem from looking at them against the wall (without Chroma Keying).

As i say, it was close…maybe 5-10%(ish) of the subject’s face blended into the background when i got the tolerances about right, (although their clothes worked fine). There was an element of aliasing around the edges of the subject, presumably that’s the affect of my DV Cam, (as opposed to pro gear), but that was more than tollerable for my purposes…i guess i’m just being a bit picky really (but for the sake of information it’s worth mentioning).

Yair, thanks for the link which shows how easy it’ll be to do on a tight budget. I think i’ll be able to pull it off with a vivid blue, (or green), piece of fabric hanging on the wall. There was actually an advert on the page you directed me to selling something which would do the trick for $14.99, so i’ve emailed them to see how much the postage to England would be.

Living in England we don’t get many gorgeous blue skies provided by mother nature, although no doubt that’d be pretty good…shame about our miserable grey weather here.

I’ve been out looking for fabric, (or paper as Andrew suggests), but i’ve not found anything which is neon bright enough yet, (and that will fold without leaving any obvious creases), but i’m sure i’ll find something suitable soon.

Thanks for all your advice and suggestions, it’s much appreciated!

All the best,
John

#92474
Jan 8, 2007 at 9:06pm

Hi there,

I’ve made a standalone on Tiger (pwbook 1.67, OSX.4.8, QT 7.1.3, Max/
MSP 4.6.2, Jitter 1.6.2).
It runs perfectly on Tiger but not on my other powerbook (Titanium
800, OSX.3.5).
Is it normal ?
Many thanks
Patrick

The crash log said :

**********

Host Name: Ordinateur-de-taprik.local
Date/Time: 2007-01-08 22:00:38 +0100
OS Version: 10.3.5 (Build 7M34)
Report Version: 2

Command: Lax 2.0b1
Path: /Users/taprik/Desktop/Lax 2.0b1.app/Contents/MacOS/Lax 2.0b1
Version: ??? (???)
PID: 619
Thread: Unknown

Link (dyld) error:

dyld: /Users/taprik/Desktop/Lax 2.0b1.app/Contents/MacOS/Lax 2.0b1
can’t open library: /usr/lib/libstdc++.6.dylib (No such file or
directory, errno = 2)

#92475
Jan 8, 2007 at 9:30pm

On 8 janv. 07, at 22:10, patrick suchet wrote:

> Hi there,
>
> I’ve made a standalone on Tiger (pwbook 1.67, OSX.4.8, QT 7.1.3,
> Max/MSP 4.6.2, Jitter 1.6.2).
> It runs perfectly on Tiger but not on my other powerbook (Titanium
> 800, OSX.3.5).

Hi,

I think 10.3.9 is required for 4.6.2. So You may need to upgrade your
titanium to 10.3.9.

Best,
ej

#92476
Jan 8, 2007 at 10:23pm

#92477

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