HLVG - Collateral Damage

[Stub Mandrel]

I've done some tests and I'm now convinced of something I only suspected before.

HLVG takes out yellow as well as green. Its not just acid-yellow like lemon coloured stars that go grey (which would be OK) but its everything yellow so you are left with reddy-orange stars that should be  a warm yellow. It can also tip a nearly balanced image with a hint of green into being one dominated by a red and magenta cast in the background (something I see a lot, especially in Startools processed images, but that appears to be accepted where green would not be).

This is a real killer on subjects like M31 where you want that rich 'light bulb glow' in the middle.

I'm finding that simply reducing the saturation of the green channel has a more pleasing effect.

Do other folks see the same effect? Or have I got funny eyes?

[Jonk]

My first reaction - is your screen colour calibrated? Have you looked at the same image on a couple of other devices?

 

[Stub Mandrel]

@Jonk Thanks, yes I have spent a fair while on monitor calibration.

I have just done a test, using pure red, orange, yellow, green etc. and pastel equivalents.

Original image:

As expected the normal setting gets rid of green but it also turns strong yellow completely orange. This is the effect that is spoiling my images making every pale yellow star a dull fawn:

The medium setting is clearly gentler on yellows, and is probably what I will use in future, although it doesn't eliminate green as well as I would like:

The weak setting doesn't affect yellow much, but has only a very gentle effect on green:

Some playing around suggests the best results are to combine the weak or medium setting with reducing the lightness and saturation of the green channel. This means you can tailor the depth of the effect.

 

[michaelmorris]

If you are concerned about a possible effect on star colour, why not create a layer mask for the stars so that they aren't affected by HLVG.

[Stub Mandrel]

Good idea. This image is a recent example where even medium HLVG made the two larger yellow stars turn brown:

 

[ollypenrice]

I use SCNR green in PI, on which Rogelio's plug in is based, but as with most things I do in PI I export it into Ps to use as a layer so I can select where and by how much to accept it.

Olly

[Stub Mandrel]

Now I'm getting the hang of layer masks, I think next time I'll try restricting it to the background