Help Removing Light Pollution From Bottom of Photo

[vtrjames]

Hello,

I shot the following image back last week on a clear night in not a particularly dark area. However, the light pollution is particularly bad at the bottom of the photo. It is a stacked shot of 90 lights and 10 darks. I've attempted to remove it by adjusting the different colours for low, mid and high tones but now I'm at a dead end. Is there anyway I can remove it to an acceptable level?

Photo...

Orion Attempt One by vtrjames88, on Flickr

Any help would be hugely appreciated!

Thanks,

James

[JamesF]

There's a photoshop plugin called gradient exterminator that might do the job for you.  I don't think it's free though.

Alternatively I guess it might be possible to do something like:

copy the image

blur it to remove the stars

subtract the blurred image from the first

take the blurred image and replace the orange/red area by blues of similar tone to the rest of the sky

add this back to the original

I'm no photoshop jockey though.  There may be better ways to do it.

James

[iksose7]

I would go into PS and hit CRTL+U to bring up the hue/saturation panel. On the box where it says master, drop it down and select any colour. That should make the 3 little eye dropper tools below active. Select the one with the + on it then click the bottom of your image where the pollution is. You can then play with the sliders to decrease the glow/colour to your liking. You can also combine the method above with the use of a lasso selection and feather around the area if need be!

James' advice above about gradient exterminator is sound though, i would try that first if you have the plug in.

Callum

[PeteC]

If you've got Photoshop you can download Gradient Exterminator on free trial (full licence USD 49.95). I've just downloaded the trial today and it's already worked wonders on some hard to fix gradients.

[Alien 13]

The method i use (it will remove the blue sky colour however) is as follows.

Copy the image.

Use the noise tool dust and scratches to remove the stars use the minimum settings you can get away with.

Gausian blur (a little) to remove any noise artifacts.

Invert the image so its a colour negative and open levels.

Use blend mode colour burn and adjust the levels above very slightly to brighten the image a little (this prevents the black level ending up at zero).

Adjust the levels and blending percentage (I normally go 95-100%) till you are happy

Hope this helps

Alan

[Steve Ward]

Try this .... 

[vtrjames]

Thanks all, I've got a busy few days ahead but I'll be sure to give your suggestions a go!

Many thanks and merry Christmas!

[neil groves]

When gradient correcting, is it best to gradient correct near the beginning of the processing, or wait till it's fully processed and then gradient correct?

I am currently working on an image with this issue.

Neil.

[MattJenko]

Gradient removal is one of the first things I do in my workflows as it is all pervasive and makes everything else more difficult.

[vtrjames]

I'm currently running the evaluation version of the Gradient Exterminator plug-in, it's very good (thanks for the pointer!). However, it appears to remove all colour from the image and I'm unable to increase / decrease contrast levels or carry out any further processing. I'm guessing I'm doing something wrong but it's really frustrating me; I realise this is probably a pilot error but have you any tips?

Thanks,

James

[lensman57]

I'm currently running the evaluation version of the Gradient Exterminator plug-in, it's very good (thanks for the pointer!). However, it appears to remove all colour from the image and I'm unable to increase / decrease contrast levels or carry out any further processing. I'm guessing I'm doing something wrong but it's really frustrating me; I realise this is probably a pilot error but have you any tips?

Thanks,

James

How are you using the gradient xterminator?

A.G

[lensman57]

Here is a version with a bit of messing about in PS. I don't know what software you are using for processing but you need to crop the edges quite a bit to get rid of the stacking artefacts as these will cause false results for flattening the back ground , the image is a nightmare to process as you have complex gradients, LP, uneven illumination, Sky glow and vignetting. next time do not image so low in the heavy LP zone, no LP filter no matter how expensive is going to remove that much LP and all you end up with is weak signal and noise. Hope that you are not too disappointed with this effort. 

Regards and best wishes.

A.G

[vtrjames]

Apologies for the late reply. I've been loading the file into Photoshop, running the filter and then making adjustments. When using the filter I had been selecting medium aggression (off the top of my head) and then making other adjustments such as curves and levels.

James