3025EMC Master Control Switching & Channel Branding
Page 142 Revision 3.0.3
7.1.2.1. Introduction
The user will require two items in order to insert an image into the video. One is the image or artwork
to be displayed, called the “fill”. The second is a black and white image, called a “key”, that is used to
tell the hardware where to display the image and where to display the background or video signal.
Where the key is black, the video signal will be visible. Where it is white, the fill will be visible. Grey
areas will display a "mixed" value that is partially the background video and partially the logo image
depending on the brightness of the key's gray value.
7.1.2.2. Types of Keys
Overture™ software can take an image and extract a key signal out of the image based on a colour
that is selected as the background colour. This is called "chroma keying" because the colour selected
will be the used to create the key. The software takes an image and a selected colour and then creates
a key that is either black (in areas where the image matches the selected colour) or white (otherwise).
The resulting key is a black and white image with hard edges between the background/foreground.
This is called a "hard key" because of the resulting hard edge between fill and background. The
Overture™ software will "soften" the edges so as to not violate any video bandwidth restrictions.
This "self key" technique may work fine for simple, few colour images, but if the background has subtle
changes or it bleeds into the foreground image, the edge between the background and fill will be
jagged and will not always follow the contour of the fill.
For better results the user can supply a key image that is created at the same time as the source
image with the keying effect in mind. Copying the fill image and converting the foreground area to a
gray level that is proportional to the desired mix value creates a key. Softening (sloping) the edges of
the key will in turn control the "hardness" of the background/fill transition.
The key file must have the following characteristics:
1. It must be the same Horizontal and Vertical size as the fill.
2. The image in the key file must have the same Horizontal and Vertical location as the image in
the fill file.
3. The file formats must be the same.
4. The key file must be black and white only. This means that Red, Green and Blue must have the
same numbers everywhere in the file.
7.1.2.3. Translucency and Drop Shadows
Many times it is desirable to have the whole logo or an area of the logo translucent. This means that
both the fill and background are visible in a mixed proportion (i.e. 60% fill and 40% background). For
instance, a drop shadow around an object consists of a background mixed with a colour (usually dark
gray). It is not imperative that the overall transparency is correct when the artwork is being designed.
The overall transparency of the logo can be adjusted in three places: in the original key image, in the
Overture™ software and in the EMC hardware. For best results, ensure the original key has the proper
scaling, particularly when there are various regions of differing translucency.
If the user is drawing a separate key and fill, translucent regions can be created by placing gray over
the desired areas. Bright gray will include more fill than background and dark gray will include more
background.
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