How to prevent or get rid of Blue star halos...advice please...

[StargeezerTim]

Hi all,

I have been experimenting with LAB colour on my M42 image. After going as far as possible stretching in RGBG colour, I then use levels to boost colours. I also added a luminence layer in photoshop CC. The problem is, whilst colours are boosted and the effect is great, it adds blue halos to the stars.

Does anyone know of any effective ways of preventing or dealing with this. I have tried 'replace colour' with varying degrees of success. I also used the 'reduce blue star halo' in Noels actions which really makes things worse.

Thanks in advance... Tim. 

[Davey-T]

If you've got P'Shop you can remove the stars and process the background and stars separately.

Dave

[StargeezerTim]

If you've got P'Shop you can remove the stars and process the background and stars separately.

Dave

I've tried using a star mask clipped to a layer, is that what you mean? How do get two separate layers, stars and background?

[ollypenrice]

I'm not sure you're using Lab colour as effectively as you might.

Once I have the RGB as well stretched as it wants to go (I don't touch Saturation - too noisy) I save that and then go into Lab colour. Here I use the bog standard contrast tool on 'a' and 'b' channel and boost it by about 35 on both. I then take this back into RGB mode.

Now sometimes (I don't know why) the conversion to Lab colour black clips the image. If it does, fear not. Just save the Lab-modified image and paste it on top of the pre lab-modified image and go for blend mode Colour. This will ignore the changes to brightness but preserve those made to colour.

It looks to me as if your main nebula is too bright. This will reduce its apparent colour saturation.

You can bring down large soft haloes using Curves but I think the stars you have here are natural to the imaging rig you have and I'd be inclined to leave them. You'll see similar effects on professional images, after all.

Olly

[astromerlin]

You could use Straton star removal tool if you dont like PS methods.

https://secure.shareit.com/shareit/product.html?sessionid=2723521289&random=ab9f996b8d9cd1eecb762558e6858e0b&productid=300568169