Explorations Of Our Digital Future
Blue Screen Chromakey
Written by Jeremy Garrett, Edited by Tom Walker, Copyrighted Feb. 2006 —Jan. 2007
Every time we turn on the television to check our weekly weather forecast, we are
witnessing the technology of image manipulation. In order to create weather forecasts, the
weather channel uses a technique known as
blue screen chromakey
. What this does is transplant
the foreground of one image onto the background of another image. In this lab, you will take two
images, including a “foreground” picture of yourselves (which you will take in front of a blue
screen) and a “background” picture of your choice, and then you will use either “blue screen” in
order to produce the same effects that are used on TV and in the movies.
prohibit using new, unique pictures, samples will be provided.)
Part 1 –
Taking and Preparing Images:
Part 1 – Procedure:
Assuming that digital cameras are available, take turns taking each other’s picture, and
helping each other copy those images into the appropriate notebook computers.
(If this is
not possible, please request a sample image from your instructor.)
Open both your foreground image and your background image into MS Windows Paint.
(Click Start/Programs/Accessories/Paint or right click on the files and then select Open
With, and then choose Paint).
For each file go to Image/Attributes, under Units select Pixels, and then write down the
width and height.
In order to combine the two images, they have to have the same digital
parameters: #of pixels wide, #of pixels tall, and #of bits per pixel.
To guarantee that our files have the same number of bits per pixel (sometimes
called “color depth”) simply save the image as a 24-bit BMP file.
To match the sizes of the images, we can crop, stretch, or skew, etc. either or both
Feel free to play with it and see what might be esthetically appealing.
you are unsure, simply use the Image/Attributes command and set the number of
pixels wide and tall for the big picture to the same size as the small picture.
As an alternative method, you may create a new, blank image in Paint, and then
use the attribute command to change its size to match the background image.
You can then copy and paste your foreground image into this blank image.
has the advantage of letting you reposition the image.