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Pan Merge Side Effects
Panchromatic Merging: HSV and Brovey
HSV and Brovey merge are two methods of combining the low-resolution (30m) color information with the higher-resolution (15m) monochrome information from the panchromatic band. This increases the detail in the resulting color image, but typically alters the colors either brighter or darker. This has the result of skewing some colors to odd shades. For example, dark evergreen forests often show up much brighter in the Panchromatic band, because the Pan band captures some infrared wavelengths, where vegetation reflects strongly. As a result, a dark evergreen forest may end up a bright pistachio green after either Pan Merge technique.
Compare these images:
30m RGB Bands
15m Pan Band
As you can see, when you replace the monochrome portion of the 30m data (upper right) with the considerably-lighter but more detailed representation from the 15m Panchromatic band (lower left), you get more detail (lower right) but the colors are skewed with respect to the original 30m color data (upper left).
This is most evident in areas of green vegetation, which tend to appear darker green in the visible RGB bands of the 30m data, but reflect very brightly in the infrared band that is also captured in the 15m band, inevitably skewing the 15m band to be much brighter in these areas.