Chroma key question

wayneout · Post by **wayneout** » Sat Jun 04, 2005 12:13 am

Hello,
Hopefully, I can explain this correctly. There is a sample mpg that
you can use for chroma key. It is a picture of a girl with a camera
walking forward with a camera. The background is a light green.
I have used this for learning purposes and it works good.
When you go to "chroma key", the green color is already picked for you
and then you can just hit the right key and it works perfectly. (This is
the part that was hard to describe about the color already being there)

When I bought Video Studio 9, I bought the blue screen for the background. I shot a small video with the blue screen as the background.
There was no other color of blue in the mpg. When I hit on the chroma
key screen, the color that was picked was black. Using the color picker
is not that easy for me for some reason. And it doesn't work as well.
So, my question is why would the program pick the green color automatically for the sample video and not pick the blue color for the other mpg. Is it something I am doing wrong? Maybe the light source
gave more than one color blue in the video.
As for the color picker, there is very little info on it in my manual.
I send a letter to support to ask them. However, they came back with
just "use the color picker"
I own six Ulead programs and I have never be able to get any support
for them that helps me.
Thanks,
Bill

mell · Post by **mell** » Sat Jun 04, 2005 1:34 am

Hi wayneout,

While I won't attempt to answer why Ulead automatically picked the right colour from the sample video. I'd like to help you on the use of the colour picker.

Can you elaborate a bit more when you said:

Using the color picker
is not that easy for me for some reason. And it doesn't work as well.

1. You're unable to use the ink dropper (colour picker) tool?

2. To what degree of a result have you obtained? Didn't worked in masking out the whole background? Blotchiness or irregular transparency in the background? etc.

I work with blue screens too and best results come consistent with an evenly illuminated screen. So you'd need diffused light sources to at least illuminate from at least 2 sides (usually left & right of screen).

Also make sure that the subject does not cast a shadow on the screen.

Recheck your setup and see how little variations in lighting affects the on-screen effect.

Cheers!
mell
[/quote]

wayneout · Post by **wayneout** » Sat Jun 04, 2005 1:51 am

Thanks for the input.
I think my first mpg had different variations of the blue, but I
don't remember right away. I was so unhappy with the results,
I deleted it. (it was just a test for me)
If you don't mind, a few questions about the lights.
Would shooting outdoors work better?
What kind of lights do you use on the left and right?
ie spotlights, regular lightbulbs, etc.

One of the problems was that the screen that was shipped had
wrinkles all in it. I didn't know if my wife could iron it or what.

The color picker seems to be beyond my workings. Do you move it
to the blue screen in your workplace to pick the color? It seems I
was trying to pick the color from pallette. I really am not sure
exactly how to use the picker.
Thanks for any help. I really like using Video Studio and had
great results from V8. The only reason I upgraded to V9
was the chroma key.
Bill

mell · Post by **mell** » Sat Jun 04, 2005 2:18 am

Hi Bill,

Ok ... enough details for a solution attempt.

Firstly, you've have only gone as far as being able to pick the background screen colour from the palette; that is not good enough as you won't find a near perfect match of the actual colour.

Take a closer look right next to the colour picker area, you'll see an ink-dropper icon. That's what you can use to simply pick the colour off any parts of the preview window. (If you have ever used programs like Adobe Photoshop you'd be familiar with this tool).

Try that first, it shouldn't be that unwieldy.

Next on lighting ...

I've been using standard studio lights (meant for still flash photography) and light up the screen with the incandescent modelling lamp built-in. As it's slightly yellowish, I'd have to adjust the white-balance first.

For simplicity, you may even try to use 4-feet fluorescent tubes on each side. In any case, always adjust the white-balance on your camera using a piece of white paper or cloth under the intended lighting conditions first. (fluorescents give off a greenish tint)

Nothing beats the outdoors ...

That's the best alternative. Where the opportunity allows, shoot outdoors. Any time of day when the sunlight is not harsh with undue shadows would be excellent for shooting. You'd have to supplement with a reflector (improvise with a white styrofoam or paper cardboard to illuminate the subject properly).

Hope the above helps. First go back to your PC and try the ink-dropper selection tool.

Mell

LGO · Post by **LGO** » Sat Jun 04, 2005 4:29 am

mell wrote:Hi wayneout,

I work with blue screens too and best results come consistent with an evenly illuminated screen. So you'd need diffused light sources to at least illuminate from at least 2 sides (usually left & right of screen).

Also make sure that the subject does not cast a shadow on the screen.

Nice tips, but I'll go ahead and be the Village Idiot tonight and ask; If you illuminate the subject from both sides, how can you not have the subject cast shadows on the screen?

Regards,

LGO

mell · Post by **mell** » Sat Jun 04, 2005 5:04 am

Hi LGO,

Sorry if the explanation was not crystal clear. I only had the illumination of the blue/green screen in mind when I prescribed lighting it from both sides. You'd need supplementary light(s) for the main subject.

Note though that you can get pretty balanced shadowless lighting using umbrella diffusers with the still photography setup that I'm using.

It would also help if the subject do not stand too close to screen (I find at least about a metre and a half as appropriate for close shots).

Thanks for pointing it out though.

Village Quack Doctor

mell