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Star reduction discussion, anyone?


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I had never done much star reduction till recently and used Noel's Actions for a quick zap when I did.

But now that I am doing lots of camera lens stuff there is a real need to reduce, drastically, the entire stellar population of an image. So far I have created a feathered star layer (using Noel for speed) and then given it a huge whack with the Minimum filter and used Edit-Fade Minimum to let the stars back up to an acceptable compromise between smallness and side effects. I resize the image up a lot so I get more control before doing this.

Lastly I take a close look at the starfields and see if Colour Select can identify the artificial side effects newly created around stars. So far it has been good at doing so which means I can get the artefacts to look like the background sky using colour balance and levels. This has to be done as a layer to avoid such areas as are adversely affect by this stage.

I wonder what other tequniques might be out there and work better? What am I missing?

This stars here are mightily reduced from standard working as above. I'd rather not do it at all but with lenses that isn't an option as far as I can see.

Olly

1188334455_yG63d-X2.jpg

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"a huge whack with the Minimum filter", I must try that!

I usually lift the stars out of the picture onto a new layer by Duplicate Layer - Image, Adjust, Threshold (adjust to taste) - Magic Wand to select the background (all black, don't select the stars) - Inverse Selection (clean up in Quick Mask if necessary) then expand the selection by one or two pix and then feather it by one pix.

Delete the threshold layer and Ctrl J for a new star layer and then shrink the stars on the underlying layer using the Minimum filter. At this point there will be no visible change because the new star layer is on top of the layer you have just filtered.

You can then shrink the stars on the star layer using a bit more subtlety. With any luck the star layer will still cover the underlying layer's stars (due to the expansion/feather) and any shrinkage artefacts.

Try it on a simple picture or a crop. A few attempts at it and you will be convinced!

Dennis

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Looks pretty good to me - one thing I've started doing while the stars are selected with Noel's actions, is to tweak the saturation to bring out the star colour a bit more.

One suggestion I have got for imaging through the camera lense (and you're going to hate this) is to close the aperture down slightly. A wide open aperture will give bloated stars whereas stopping down a bit will reduce the bloat - yes I know it means longer exposures but I think the benefits out weigh the disadvantages. Worth a try anyway but I do appreciate we're dealing with low signal targets here.

Regards

John

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Being a newb... I've found it difficult to comment on some images due to the amount of stars, in landscape parlance (my photography genre) they are what I call busy and so your eye wonders around without finding the area of focus because of everything that's going on.... Less is more.

It's probably not the thing to do so hope you don't mind (I'll remove it if it isn't) but I

Select Color Range (Sampled Colours) 60%

Then feathered this (at this size 1 px)

Layer via Copy

Then Blended by difference.

It will be interesting to here thoughts on why a lot of stars are seen as good.

post-23112-13387753312_thumb.jpg

Edited by Penfold
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Being a newb... I've found it difficult to comment on some images due to the amount of stars, in landscape parlance (my photography genre) they are what I call busy and so your eye wonders around without finding the area of focus because of everything that's going on.... Less is more.

It's probably not the thing to do so hope you don't mind (I'll remove it if it isn't) but I

Select Color Range (Sampled Colours) 60%

Then feathered this (at this size 1 px)

Layer via Copy

Then Blended by difference.

It will be interesting to here thoughts on why a lot of stars are seen as good.

BTW, this looks much better vertical, north up, but doesn't fit that way.

Feel free. I think that lots of artefacts have been generated here, though, paricuarly in the fainter nebulosity whch has different boundaries.

I don't think lots of stars are seen as a virtue in an image like this. Rather the opposite, I am trying to get them much smaller (on the original you don't see much else behind them.) I don't want to remove them because, after all, they are there but in a perfect optical system they would be point sources.

I have dreaed up a new method in the night and will give it a go today...

Harry, thanks, I will look up your video.

Olly

Edited by ollypenrice
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I had a quick play in PI and used morphological transformation/amount 0.5/structuring element:21. Seems to have killed a lot of stars!

David

Edit: did it properly with a star mask this time:)

post-21430-133877533341_thumb.jpg

Edited by dlp
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Feel free. I think that lots of artefacts have been generated here, though, paricuarly in the fainter nebulosity whch has different boundaries.

I had to reduce it to 35% when saving to jpg which is the cause of some of it.

However I much prefer David's effort. :)

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The advice given above sounds good but I just wonder why you need to reduce the stars ... I like to see them ... is it just for pictorial effect?

Yes, really that's it. Straight from the camera lens, due to its small aperture, the star sizes are grossly disproportionate. They dominate the real subject, the nebulae, to the point of semi-obliteration. I want to keep them but cut them down to size.

SInce my pictures are just pictures, not scientific, pictorial effect is pretty much all I have to offer!

Olly

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