The Green Screen

Thursday, July 4, 2012
American Independence Day

The Green Screen

    You've undoubtedly heard of the technique called  green screen, but didn't ever use it, or maybe you didn't know how to use it. Basically, the technique started in Hollywood. The technique is used to "extract" people when photographed against the green screen, and then place them in a new scene.  

    What you do is light the people with the same lighting (intensity, angle, height) as the new scene.  You then film them (movie or still camera), extract them, and then place them into the new scene. So, for example, you could photograph them in the studio, then place them in a gladiator arena, such as in the movie "Gladiator". 

    The reason the colour green is used is that it's the opposite of  magenta, which is a colour close to your skin tone. Thus it's then easy to select the green and then remove the people and their clothing and props from the green.

    You usually light the green at least 2 f-stops brighter than the subjects. For today, I did a fast set-up and didn't set the lights for that exposure difference. Also, whatever area is not in the frame (green), you try and use black material or seamless or black cardboard. What this does is to prevent the green from reflecting light into the areas that are going to remove from the green. Later on, I'll explain and give an example of what I mean .

    For today's example, I used a newly-acquired Hoge pressed steel car, circa the 1930's.

Here's the Hoge Car on the Green Material

You can purchase an actual "green screen" material on e-Bay, or you can buy material from any wholesale fabric store. Most stores where women buy fabric to sew their own dresses will have such material. 

Be sure to go on the net to check out the specific colour of green that you want.

In the above example, the green is overexposed as the car paint was dark, thus the overexposure.

In Photoshop, you'll use the Select >> Color Range Tool

Notice that parts of the car were also selected.

You need to adjust the "Fuzziness" slider to reduce any green colour capture from the use of  the Select>>Colour Range.

As you select, you can also use the + or - eyedroppers to add or remove parts of the selection.

Notice in the above screen capture, how I've adjusted the - eyedropper to further remove the dark green shadow under the car side.

IWhen you make the selection, the side panel will show the colour selected.

You'll need to change that to the regular white, otherwise, when you extract the green, it will be replaced with the same green.

To revert to the black and white colours, just press on the green above.

That will bring up a colour window, whereupon you simply select white.

Here is the "extraction".

It's for sure imperfect, but that will happen.

What I'll do now is simply to do another select>>color range

 to further remove more unwanted green.

Here is the second stage of selecting green for removal.

Better, but still not "perfect".

From here, I could do another Select>>color range.

Instead, I'll simply use the eraser tool to remove the remaining.

The Final Result.

Ugh!  Green Tires

At the beginning of this instalment, I mentioned that you had to add black material,

 black cardboard, or black seamless around areas of the car not in the camera frame.

What this does is to prevent the green material from reflecting green into the car.

That's why the tire is green!

So now you know what the green screen technique is all about.

It's a useful skill to know, but if you're good at Photoshop there are 20 other ways to remove the car from the background.

So to all of my American readers, have a wonderful 4th of July. 

 To the rest of my readers, as always, have a fgreat morning, afternoon, or evening, wherever you are.