by Chris Peterson » Fri May 21, 2010 1:54 pm
biddie67 wrote:From my untrained eye, their color substitution choices don't make any sense - why not assign a 4th color for IR and keep RGB as RGB?
There is no fourth color. Ultimately, the multispectral data has to be assigned to the three available primaries, which are red, green, and blue for most display devices (and approximately that for the human eye). If you have three data bands, you can arbitrarily assign them to RGB according to what seems to make the data most clear, or even based on aesthetics. If you have more than three bands (as is often the case), you need to apply some sort of mathematical model, mixing ratios of different bands before assigning them to either red, green, or blue. More complex models may mix input bands and then split them into output mixes of red, green, and blue- something like your idea of adding a fourth color, but not exactly.
It is often desirable in images like those posted above to deliberately force the color scheme away from RGB, since a completely unnatural appearance actually makes it easier for people to see details that might otherwise not be noticed.
[quote="biddie67"]From my untrained eye, their color substitution choices don't make any sense - why not assign a 4th color for IR and keep RGB as RGB?[/quote]
There is no fourth color. Ultimately, the multispectral data has to be assigned to the three available primaries, which are red, green, and blue for most display devices (and approximately that for the human eye). If you have three data bands, you can arbitrarily assign them to RGB according to what seems to make the data most clear, or even based on aesthetics. If you have more than three bands (as is often the case), you need to apply some sort of mathematical model, mixing ratios of different bands before assigning them to either red, green, or blue. More complex models may mix input bands and then split them into output mixes of red, green, and blue- something like your idea of adding a fourth color, but not exactly.
It is often desirable in images like those posted above to deliberately force the color scheme away from RGB, since a completely unnatural appearance actually makes it easier for people to see details that might otherwise not be noticed.