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Gradients - help and advice please


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One of my biggest headaches when processing, is gradients. All my images have a gradient like the one in the attached image (dynamic background extraction image in Pixinsight). Always green bottom left to red in the top right. This gradient is typical of all my images regardless of orientation of the camera, and whether or not darks or flats are used. For that reason I'm not really sure why it's always there.

Anyway, presuming I can't find the cause and just have to eliminate it, I'm looking for best solutions - at the moment I use the dynamic background extraction in Pixinsight, but it's very slow, long winded and tedious to do.

Some time ago I was shown how to remove a gradient using Adobe's own gradient tool which I remember worked very well, but I can't for the life of me remember how to do it.

Any help or suggestions would be really appreciated. I know Gradient Exterminator works well but I don't have it and there is no money to buy it at the moment, so solutions have to be free ones, or methods using my existing software (Adobe CS3, Pixinsight and PSP7).

Thanks

John

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That's a strange one. The only time I've had gradients like that in my shots is when I've had my LP filter in the optical path with my DSLR.

It is possible to remove gradients by hand in photoshop as I'm sure you've found out from googling. However I've found that the simplest solution is to use one of the sets of astronomical actions. I know you were looking for free options, but it's a lot cheaper than Gradient Xterminator.

For reasons of cheapness I've bought Peters Actions for Astrophotographers¹: the Yellow and Orange sets - costs a whopping £7.60 and seems to deal with my gradients quite nicely. Though I only have ones that are bright orange at the top and intense orange at the bottom, from streetlights.

[1] Just to be clear, that "Peter" is not me, nor anyone I know

Edited by pete_l
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Thanks for the replies.

Dennis - thanks for that - at least I've rediscovered how to deal with gradients in Adobe - unfortunately with such a severe gradient I'm finding it impossible to eliminate it by this method.

David - yes I'm using DBE in Pixinsight at the moment as I haven't found anything better so far but I do find it a bit hap-hazard at times and it does seem to effect the brightness of the stars (dims them) on the red side of the gradient.

If I could establish what is causing such bad gradients it would help enormously. As i understand it, amp glow is not a major problem for the EOS1000D like it was for the old Canon 350. The darks and flats don't seem to be the problem - I've taken fresh flats to make sure. I've also processed without flats and darks to make sure. I am using an EOS clip filter but I wouldn't have thought it would cause a gradient. LP is horrendous here in Chester but I'm not convinced that's the problem as it doesn't matter what the orientation of the camera is. That would lead me to believe it is the camera itself that's causing the gradient.

Any more thoughts on this would be greatly appreciated

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I use the GradientXTerminator Photoshop plugin from rc-astro.com. A standalone version is also available. It's very easy to use and is extremely effective. It will remove color and luminance gradients, and will also neutralize the background. I would be helpless without it!

-Joe

Edited by RoundStars
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John -

There are many methods in PS to reduce the gradients if you don't want to buy something like GradientXTerminator.

I am attaching a file of two PS actions zipped together for you to give a try. Hope they help you. Lemme know.

Obviously finding out what exactly is causing the gradient to reduce/remove it is best but give these a try in the meanwhile.

Gradient Removal Actions.atn.zip

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