home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Light ROM 3
/
Light ROM 3 - Disc 2.iso
/
programs
/
amiga
/
rgb2ire
/
readme
next >
Wrap
Text File
|
1995-01-31
|
1KB
|
31 lines
Notes for "rgb2ire"
Ernie Wright
ernie@gaspra.pd.com
31 Jan 95
rgb2ire displays NTSC composite signal amplitude in IRE units, given
RGB triples.
Digital images like those produced by LightWave are stored as an array
of rectangular pixels. The color of each pixel is defined by levels
of red, green and blue ranging from 0 to 255. When these images are
recorded or displayed on television equipment, the pixel RGB levels
are read off a line at a time and converted into several sine waves
that are added together to form a signal.
The IRE (Institute of Radio Engineers) units used to measure video
signal level are scaled so that maximum white (255, 255, 255) is 100
IRE. Because of the way black-and-white and color information are
mixed to form a color signal, some RGB triples translate to video
levels that exceed 100 IRE. Fully saturated yellow (255, 255, 0) and
cyan (0, 255, 255), at 131 IRE, are the most extreme examples.
The hardware limit for video level is 120 IRE, and in general, colors
that encode to levels above 110 IRE are said to be too "hot." The
intensity or saturation of such colors must be reduced. Although you
can often rely on the encoder hardware to make this adjustment on its
own, it's better to know what part of RGB space is affected by video
limitations and avoid creating those colors in your art.