How do you battle with LP gradients

[RichLD]

On 28/08/2018 at 21:06, ollypenrice said:

I follow Rogelio Bernal Andreo, Harry Page and other PI gurus in thinking that fewer and better background markers work best.

Amen! I fiddled with DBE for a couple of years before realising this - it's so easy to wipe out swathes of nebulosity when adopting an overly surgical approach.

[ollypenrice]

On 29/08/2018 at 23:07, souls33k3r said:

 

Pardon my naivety but how does one differentiate a colour gradient from a LP gradient? Do colour gradients exist in when using mono camera images?

 

A colour gradient, however caused, is just an artifice in the form of a drift in colour balance across the image. You might have a background sky drifting from overly green to overly red, for instance. It's easy to be sure in the case of background sky because the 'empty' sky should really be about equal in R, G and B. You can measure small sample areas (in Ps for instance) to compare the RGB balance in different places. I think more often than not that colour gradients do arise from LP. I also think that the eye is very sensitive to colour, so you might look at the individual channels and think that the sky was even, but once seen combined in colour you see a drift quite easily.

You'll get this using a mono camera with colour filters, certainly. I think I've only done one RGB image in the last ten years which had nothing at all to correct.

If you use DBE or ABE in Pixinsight it will give you a gradient map which can be considered a photograph of your colour gradient. They can be quite alarming - and I'm shooting in skies with an SQM usually between 21.5 and 22.

Olly