bow to do a blue screen correctly

[stran]

Hi,
Please help me figure out how to do a blue screen, every time I do one, the color of the image on the blue screen shifts (losses its blue color?)

This is what I did using photoshop set in RGB color mode:
1) created a completely blue background by selecting R=0;G=0; and B=256
2) I past the image, red heart
3) save the image as a jpg, set on the lowest compression, highest quality

I then followed the instruction in the manual and I get the heart superimposed on the video, as it should. But, the heart appears to be pink?

Should I save under a different format?

thanks
sam

[fluggo99]

What are you using? Premiere or MSP?

They could be doing the same thing. Whenever I try to do the "bluescreen" effect in MSP, all my colors shift, too, and there's nothing that explains why this happens.

What I have to do instead is use the "chroma key" effect, which as far as I can tell does mostly the same thing, except you can't get shadows that fall onto the blue background.

[DrMordrid]

There are several ways to do "bluescreening". Actually you can use any color including blue or green. Some work best for video clips, some work better for overlaying still or animated graphics.

My thoughts: use bluescreen for video and use other keying methods for graphics or animations.

Try using a black or white background and a lumance key instead of the bluescreen key. Once this is set up select the keyed color as usual. Other colors can be tried using a color key.

Dr. Mordrid

[fluggo99]

Doc,

How does the "bluescreen" effect under MSP do its trick? What do I need to do to keep it from changing the colors of my subjects?

[robmcl]

stran:
I take it from your description, that you are trying to create a "bluescreen" behind your red heart, so that you can key-out the blue and get the heart to overlay your video correctly. If this is correct then......
I regularly use photoshop to do a lot of titles because a native ps file (.psd) includes an alpha channel if the background of the image is transparent. Here's how I'd do it.
Create a new ps file the size of your vid frame (eg 704x480 etc) with a tranparent background. I use 150dpi/RGB
Create your heart image as you normally would.
Save the file (filename.psd)
In MSP, place filename.psd as an image file on any overlay track (eg. V1, V2 etc - not Va or Vb)
Stretch the image file to the desired duration along the timeline.
Right click the image file - select overlay options.
Within overlay options, choose "alpha channel" - you'll find that the 'transparent' area of the image drops out perfectly.
I use this all the time.

Hope this helps...Rob

[DrMordrid]

On re-reading your first post I think I have some out-and-out guesses as to what's happening. Check 'em out just in case;

1. You're using a full intensity colors, right? By that I mean a with a level of 255? I'm willing to bet MSPro is set up to adjust the colors to match the display limitations of either NTSC or PAL.

To check this open file/preferences/edit and see if the "Apply color filter" box is checked. If it is either NTSC or PAL will also be checked to it's right.

If this control is set then MSPro will reduce the intensity of your colors to keep them in a range acceptable NTSC or PAL. Neither standard can display the full intensity colors found in 24 bit RGB images. Example: instead of using a level 255 red the filter will clip it as low as 181.

If on the other hand you want to use a full intensity colors and are going to display the video only on a computer then uncheck the "Apply color filter" box and go to town.

2. Another problem is that you're using a .JPG file as your bitmap. Since some .JPG files have altered palettes as part of their compression this can also affect your results. To be safe use 24 bit .BMP or .TGA files the same rez as your video project. .TGA files (Targa's) are better because they can be created with an alpha channel if need it.

Of course if both of the above are true then your colors could get *REALLY* screwed up.

Dr. Mordrid



[This message has been edited by DrMordrid (edited 07 December 1999).]

[stran]

Thanks for all your help. I been really busy, as it is the last week of classes. I will try some experiments tonight.

fluggo99: I am using MediaStudio Pro 5.2

robmcl: I see what you are talking about, I will give it a try tonight

DrMordrid: I will check you your first guess out. I think that is very good information for the future.

Thanks all,

Sam

[stran]

robmcl,

Your technique worked like a charm! It even seemed to render faster!!

Thanks

Sam

[robmcl]

Glad to hear it.

Using PS for titles etc, allows me to use all the filters on my text for bevel and button etc etc.
Another thing I use a lot is the gradient tool to create a background for a caption title. Eg. When I show a talking head, I often need to display the speaker's name in the lower third. PS let me create a Foreground-to-transparent gradient box as a backdrop for the text. A nice added-touch effect.

Have fun....
Rob