Greenscreen/ Bluescreen Basics
Chroma Key (color mask) is a method for
removing a specific color and replacing
it with another image.
For example, shoot a model or subject in
front of a green screen and replace the
green with a suitable background, such as
a location, interior, or weather map.
What program should I use for editing
my photos?
For professionals doing high volume there
is the Express Digital Pro line of software
- very pricey, but great for quick and painless
high volume printing. The most powerful
program for editing photos is Adobe Photoshop.
Unfortunately, it's also expensive. There
is a less expensive version called Photoshop
Elements which has nearly all of features
of the full version, and can be downloaded
for a free trial. There is a plug-in that
will make the keying process much simpler,
Primatte Chromakey from digitalanarchy.com.
Some other programs: JASC Paint Shop Pro,
Microsoft Picture It!, CorelDraw, Photoimpact
Pro, Corel PhotoPaint
How do I light the green screen
for best results?
Lighting of the green screen is a key part
of background replacement. The secret is
to get a nice even light so that the green
doesn't have too many shadows.
How do you set up the green screen
for best results?
Try to avoid wrinkles and creases, a portable
steamer comes in very handy if you have
to pack your greenscreen away after every
shoot. Also a good way to keep the backdrop
flat is to use gaffers tape on the edges.
In what format should I save my images
once I've transferred them to my computer?
The short answer: If you are editing the
file and plan to reopen it in your image
editing program later, you should save it
in a lossless format such as TIFF, or one
of the other lossless formats supported
by your image editor. (See also the discussion
of JPEG vs. TIFF below.) If you aren't planning
on changing the image at all., you should
just leave it in whatever format the camera
produced. If you've made some changes and
don't expect to do any further edits, you
should save it in whatever format is appropriate
for the final use of the image.
The longer answer: What happens when we
repeatedly load and save an image using
JPEG compression? Each time we recompress
the image, we discard a little information
about subtle variations in the image and,
because of the compression, we can introduce
slight defects in the image. As we manipulate
the image, these defects may become amplified
as we do things such as increasing contrast
or brightness. If we resave the image in
JPEG, we run the risk of introducing a new
set of errors into the image and these errors
will compound with each resave. In fact,
even if we don't change the image, simply
resaving it can compound the errors from
the previous save.
The way out of this quandary is, after
a round of editing, to save your images
in a lossless format such as TIFF, or whatever
native format your editor supports. When
you are storing in a lossless format, you
don't introduce extra errors every time
you save and load. Of course, this format
will take up much more space.
What's the advantage of TIFF over JPEG?
First you need to understand JPEG. JPEG
is a lossy compression method, which means
that some image quality is sacrificed to
make the image file smaller. The amount
of this sacrifice can be varied, though
there is no agreed upon scale. Your camera
probably has different jpeg modes, which
correspond to different tradeoffs between
quality and size.
TIFF is actually a family of compression
methods. The standard is fairly complicated
and not all programs handle all types of
TIFF files. Most programs, however, can
handle a simple TIFF format in which no
compression of any kind is applied. This
requires 8 bits of resolution for each of
the red, green and blue channels, or 3 bytes
per pixel. Thus, the total file size will
be 3xHxV bytes, where H is the horizontal
resolution and V is the vertical resolution
of the image.
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