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4th band in training?

Hi!

Has anyone made use of 4th band? From the baseline blog, it is mentioned that it is an opacity mask channel but they are removing it from images before training. If it is RGBA, shouldn’t 4th channel be multiplied with RGB instead?

I have tried transfer learning without it and learning from scratch with it, but it seems it is really not so useful. According to some basic research I made, opacity or reflectance could be predictive of weathered materials (concrete or metal) on some wavelengths, but I’m not sure if this opacity level is an indicator of that reflectance.

Any thoughts?