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Removing Chromatic Aberration using Photoshop

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smf View Drop Down
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Post Options Post Options   Quote smf Quote  Post ReplyReply Direct Link To This Post Topic: Removing Chromatic Aberration using Photoshop
    Posted: 07 March 2012 at 15:11
Awesome tips! The prevalence of CA has actually made my shy away from bird shots, as I've found it worst on dark birds against a bright sky. With this knowledge in hand, I might go back out and try to find some birds and get some good shots!

Thanks!
-Scott
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mark.t View Drop Down
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Post Options Post Options   Quote mark.t Quote  Post ReplyReply Direct Link To This Post Posted: 02 March 2012 at 10:42
Love this method of removing Chromatic Aberration. Thank you Frankman.
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Post Options Post Options   Quote geedorama Quote  Post ReplyReply Direct Link To This Post Posted: 24 June 2011 at 10:05
I use about the same method as Frankman does, but simply use a duplicate layer in Photoshop, select the bottom layer to make the adjustments, then select the top layer and use a soft eraser- brush to bring out the portions treated for CA while leaving everything else intact.
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Post Options Post Options   Quote tigertimb Quote  Post ReplyReply Direct Link To This Post Posted: 24 June 2011 at 09:11
A rather late addition to this thread, but saw the link from the discussion of purple fringing.

This is almost identical to the way that I would remove fringing, but I would normally lasso the effected area before adding the hue/saturation layer which then fills in the mask for you. You can then always paint in other areas that you also want corrected.

And used to use the same method with paint shop pro too, the only real difference being that they have a colour wheel, but you can still adjust the colour ranges by dragging the marked boundaries on the wheel.

Shoving the saturation up to 100% initially can help whilst adjusting the colour range as it then more clearly shows which bits of the image will be affected.

And I do find that sometimes I will decrease the brightness instead of increasing it, it all depends on the background - with a lattice of purple tree branches being an example.

And it gets a little more tricky when the surrounding details aren't black/white; maybe green bokeh fringing on leaves or skin against a bright sky for instance:
Desaturating the purple then gives people a grey edge which is no better, so from within the same tool/dialgoue, by adjusting the hue slider instead you can essentially make the purples into reds.
It's rarely a perfect solution, and a small adjustment often gives the best results, just toning down the purple, but enough to say that it's less prominent particularly when viewed from a sensible distance.


Edited by tigertimb - 24 June 2011 at 09:15
Tim
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Gabriel View Drop Down
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Post Options Post Options   Quote Gabriel Quote  Post ReplyReply Direct Link To This Post Posted: 26 November 2008 at 08:33
Originally posted by outback88 outback88 wrote:

It would be great if other forum members who use different S/W such as bibble, [...] , could also add their CA removal remedies

Go to the Chromatic Aberrations removal tool, move the sliders as you wish, and that's it.
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Post Options Post Options   Quote Frankman Quote  Post ReplyReply Direct Link To This Post Posted: 26 November 2008 at 07:07
Thanks for the feedback and alternative suggestions folks. I have added a postscript to the original article which deals with how to overcome the issue of desaturating areas which you don't want to be desaturated.

It's good to see other suggestions coming through as well. I'm learning new stuff too .

Frank
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Post Options Post Options   Quote wolfy Quote  Post ReplyReply Direct Link To This Post Posted: 26 November 2008 at 05:18
Well I just learnt another photoshop trick I didnt know, if this keeps up I might just learn how to PP properly. Thanks Frank!
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 26 November 2008 at 04:47
Originally posted by madecov madecov wrote:

... used a plug in called PF FREE

Actually, PFree (if that's the plug-in you mean) is designed to deal with purple fringing, which is a separate phenomenon from frankman's axial CA, which is a separate phenomenon from polyglot's lateral CA!

Purple fringing and axial CA are dealt with by subtracting or desaturating particular colors, but the problem with that is that other matching colors that belong in the scene may also be affected. For example, I can see that the purple flowers in madecov's photo have lost their intensity along with the unwanted purple tinge in the grave marker.

Lateral CA is handled mathematically by rescaling the color channels as polyglot described, so it can usually be fixed without undesirable side effects.

Edited by sybersitizen - 26 November 2008 at 04:50
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Post Options Post Options   Quote madecov Quote  Post ReplyReply Direct Link To This Post Posted: 26 November 2008 at 04:01
I'm a real novice at RAW, Have not used layers. I don't have a work flow to speak of.
I downloaded a CA "filter" plug and have played with it. It worked well in the one image I played with that was shot with a Minolta 24-85.

This is the original done in IDC


Then I used tweaked it a bit more and used a plug in called PF FREE
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Post Options Post Options   Quote polyglot Quote  Post ReplyReply Direct Link To This Post Posted: 26 November 2008 at 03:41
By scaling, I mean image-scaling. You know, a resize, but applying a different resize factor to each of the R, G and B channels to account for the different magnifications that the lens produces for each colour.

It's not something I've ever attempted manually (and it would be really difficult manually) and ufraw doesn't seem to support it , but there's a "CA correction" option in some RAW converters, at least PS CS and ACR and probably some others too, that will do it for you.

And this is for lateral CA only, but that's the common sort. Axial CA is typically seen only with large apertures, like f/2 or more, and for some reason is a bit less objectionable, at least to me.

edit: thankyou sybersitizen for posting the canonical tool for this!

Edited by polyglot - 26 November 2008 at 03:43
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 26 November 2008 at 03:41
You don't need to shoot RAW for effective CA correction - you don't even need Photoshop. PTLens handles that task and a lot more; it works as a Photoshop plug-in or standalone program; and costs just $25 for a perpetual license.
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Post Options Post Options   Quote dennismullen Quote  Post ReplyReply Direct Link To This Post Posted: 26 November 2008 at 03:34
I agree the best way to fix CA is to shoot Raw and use the lens corrections tool in ACR. There is a tool in PS too but it messes with the edges of the picture.
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Post Options Post Options   Quote Wētāpunga Quote  Post ReplyReply Direct Link To This Post Posted: 26 November 2008 at 03:19
Originally posted by polyglot polyglot wrote:

...
The best way to fix lateral CA is in the RAW processing stage, where you scale the three colour channels independently so that the image magnifications in each channel come out the same. ...


Hmm, please explain this 'scaling' approach.

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Post Options Post Options   Quote polyglot Quote  Post ReplyReply Direct Link To This Post Posted: 26 November 2008 at 03:17
Hey guys, just a nitpick, but CA has nothing to do with coatings; it's a lens-design issue wherein the image magnification is wavelength-dependent. Modern lenses like the 16-80ZA have huge CA.

The best way to fix lateral CA is in the RAW processing stage, where you scale the three colour channels independently so that the image magnifications in each channel come out the same. Result is no CA and more sharpness without damaging the colours in other parts of the image or needing to futz around with masking.

Axial CA is more difficult (and still present in modern lenses; the Zeiss 85 and 135 both show it a lot) because it's a matter of different wavelengths focusing behind or in front of the sensor plane, so bright/dark things are uniformly surrounded by a colour depending on which side of the DOF they are. Can't be fixed by scaling the colour channels independently, so Frankman's technique is probably good for axial CA.

Chromatic Aberration reference.
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