Anyone taken startrails photo in singapore before?

[jiahao1986]

Hi,

Well for stacking startrail photos, the machanism is the same as the Photoshop layer blending option "lighten", which compares the two layers pixel for pixel and uses the lightest pixel value. Since the stars are much brighter than adjecent background pixels, the stars remain.

That's why I said it's not the normal stacking we usually use for astrophoto. So, I'm not sure whether this method of stacking does improve signal-to-noise ratio, but it'll be better than normal "add" operation.

By the way, IMHO, it's better to do your own noise reduction instead of using the star trails software noise reduction as it's use a colour dark frame which IMHO, is not very effective.

Have a nice day.

Yeah I kinda know what you mean now. With my experiments with the software, the foreground does get smoother after stacking. But for signal to noise ratio for stars with respect to sky background, it might be another story, just as you pointed out.