images are those taken through narrowband filters with specific colors assigned to each filtered image, thus producing a colorful image. The arrangement of these colors is known as a Palette
. Sometimes, because the presence of SII is very low, only two wavelengths are used, typically Ha and OIII in what is known as a Bicolor Image
. The colors are also scientifically significant, allowing visualization of the location of specific elements in the object.
The most well known is the Hubble Palette, that used by the Hubble Space Telescope
when it takes narrowband images. Also known as SHO, the SII is assigned to red, the Ha assigned to green, and the OIII assigned to blue.