Chromatic Aberration????

[JulieM]

I took this image yesterday at the Canadian War Museum. The subject sculpture was backlit through the window by bright sunshine and beautifully spotlighted from the front. Obviously, I wasn't up to the task of handling this exposure challenge :o and I will try to go back on a day when the backlighting will not be such an issue. But, while I was pondering whether the image could be saved, I noticed the strong purple and green fringing in the highlights. I figured it would be a good chance to play with the chromatic aberration sliders in LR but they didn't seem to solve the problem.

Question 1 - is this chromatic aberration or not?
Question 2 - Has anyone used this tool successfully and if so can you offer me any tips?
Question 3 - Would there be another non-LR method of dealing with this?

Any help with achieving a good exposure would be welcome too! Many thanks!

http://www.pixentral.com/hosted/1GdeinMb2GnmWMdESvuxY81knGFZQ_thumb.jpg (http://www.pixentral.com/show.php?picture=1GdeinMb2GnmWMdESvuxY81knGFZQ)

[Michel B]

For me, it's not chromatic aberration, which is linked to the lens geometry (especially wide angles). This is a phonomenon, whatever its name, which is linked to the behaviour of the sensor when there is a very high contrast, typically light sky showing through branches.
The built-in tools are good for chromatic aberration, not for this.
There are different ways to correct this. They are based on selecting the purple fringe tint and desaturating it. I'm sure there are tutorials on this subject.

[JulieM]

Merci, Michel! This was taken with a 50mm f/1.4 lens and I've not noticed it before, but perhaps I've avoided the strongly contrasted subjects before.

[Michel B]

I am pretty sure your 50mm lens is not subject to chromatic aberration, like many zooms or wide angles. The reason is the very high contrast. There are actions to correct it, but with some patience you can get the best results by painting on blank layer on color mode, after having sampled nearby colours. Of course you need to paint in a selection (magic wand) or use a mask.

[Edmund]

Julie, I took a PSE-4 course a few years ago at eclectic academy and there was a section on how to remove "Chromatic Aberations AKA "the dreaded purple fringe"".
Didital images can be the victim of CHROMATIC ABERRATIONS. They can be difined as those purple, or blue highlights that sometimes will show up around lights or areas like skylines.
Just a quick rundown but in PSE or CS one would go to ENHANCE>ADJUST COLOR> ADJUST HUE/SATURATION
CHOOSE MAGENTA (OR COLOR MATCHING THE FRINGE COLOR)
SLIDE THE SATURATION SLIDER TO THE LEFT UNTIL THE FRINGE TURNS GREY AND IS NO LONGER OBVIOUS.
I have not played around with that slider in Lightroom but according to Martin Evening in his book "The Adobe Photoshop Lightroom Book" the sensors in our latest Digital camera are so more capable of resolving to a much finer level of detail then was possible with film that as a consequence color fringing sometimes becomes more apparent. Any way I hope this helps out.
Eddie:)

[Chuck S.]

I don't even see the fringing in the Pixentral image you posted. Either my display or my eyes - or both - just aren't up to the task...

Where is it most pronounced?

[JulieM]

Julie, I took a PSE-4 course a few years ago at eclectic academy and there was a section on how to remove "Chromatic Aberations AKA "the dreaded purple fringe"".
Didital images can be the victim of CHROMATIC ABERRATIONS. They can be difined as those purple, or blue highlights that sometimes will show up around lights or areas like skylines.
Just a quick rundown but in PSE or CS one would go to ENHANCE>ADJUST COLOR> ADJUST HUE/SATURATION
CHOOSE MAGENTA (OR COLOR MATCHING THE FRINGE COLOR)
SLIDE THE SATURATION SLIDER TO THE LEFT UNTIL THE FRINGE TURNS GREY AND IS NO LONGER OBVIOUS.
I have not played around with that slider in Lightroom but according to Martin Evening in his book "The Adobe Photoshop Lightroom Book" the sensors in our latest Digital camera are so more capable of resolving to a much finer level of detail then was possible with film that as a consequence color fringing sometimes becomes more apparent. Any way I hope this helps out.
Eddie:)

Thank you, Eddie. I appreciate the suggestion. Will try that tomorrrow...

[JulieM]

I don't even see the fringing in the Pixentral image you posted. Either my display or my eyes - or both - just aren't up to the task...

Where is it most pronounced?

Chuck, the purple fringing is most evident on the straight edge of the sculpture on the left hand, back side (nearest the windows). In my RAW image when viewed in LR, it extends from top to bottom of that edge. I also see green fringing around the edges of the windows. I suppose that could be something different, but the windows are actually a grey metal. Maybe I should have uploaded the RAW image...

[Edmund]

Boy now I'm really confused. On my display I can see pronounced blue edge fringing on the bottoms and some sides of the windows frames. I'll look again to see if I can pick up the others.
Chuck, you can see the fringing on the botom of all the windows even without blowing up the image in pixentral.
Eddie:confused:

[Edmund]

Just a little footnote. I recently took a image of a Grumman A-6E Intruder and the cockpit, wing edges, and any other sharp edge were frindged with a sort of blue color so much so I thought it was about 10 feet out of focus. I deleted that image so can't show you a example.
Eddie:eek:

[JulieM]

Here's a link to the RAW file if you care to see what I see. :)

http://www.sendspace.com/file/7ouqd0

[Daviskw]

Hi Julie

I am not a photographer so I’m talking about a subject with little knowledge…never stopped me before though… I think it is a conflict of white balance because of the combination of yellow and blue light.

I believe this resulted in a blue/cyan caste. You would know if the metal framing should be cyan or silver…I’m guessing silver so I removed the blue/cyan…with the result below.

Butch

http://i85.photobucket.com/albums/k69/Daviskw2004/1GdeinMb2GnmWMdESvuxY81knGFZQ.jpg

[JulieM]

Butch,

I like your results. I think the metal actually had somewhat of a blue cast to it from the reflected sky. But, I might be imagining that at this point. :confused: I'm going to have a look through my images because I recall noticing this once before. (I wish I had keyworded it with something like 'strange fringing effect' so as to make it easy to find now!) Can you tell me how you removed the blue cast?

[TonyW]

I did run the image through PTLens that has chromatic aberration adjustment and it doen't have any that I could see so I think that anything you see is purple fringing. With that lens that's what I'd expect. So the Hue/Saturation adjsutment method is probably the best way to get rid of it.

Tony

[Daviskw]

Hi Tony...I'm really confused now...I thought purple fringing and CA were the same thing...at least the same result in a photo anyway.

At any rate Julie as Tony suggested it I used a hue/saturation adjustment layer zooming in and sampling the offending fringe color then reducing saturation.

Butch

[JulieM]

Again, thanks, Butch. Uh, it makes me feel much better knowing you are also confused over chromatic aberration/purple fringing. :p I did a little googling and found that purple fringing can result from the physics of chromatic aberration but might also be caused by other things. Interesting articles:

Chromatic Aberration (http://en.wikipedia.org/wiki/Chromatic_aberration)

Purple Fringing (http://en.wikipedia.org/wiki/Purple_fringing)

Not sure where that leaves me, but the final section of the second article gives suggestions for preventing purple fringing.

[JulieM]

Thank you all! Fixing it is easy with the method you've all led me to - sampling the fringe color and reducing saturation. And, it can be done in LR, so all is good! :)

[Chuck S.]

Butch, I used the white balance eyedropper in Lightroom to change the windows to gray. Interestingly, the purple fringe on the left edge of the statue at the hand level and a green fringe on the lower edge of the window in that same vicinity remained unaffected. The green disappeared quickly with the green saturation slider.

However, the purple fringe was not so cooperative. I tried to eliminate it by driving the purple saturation slider all the way to -100 and some of it still remained. Only when both the purple and blue sliders are given large negative adjustments does the fringe lose its color - and even then there's a residual magenta cast inward from the edge.

Very pesky! Perhaps a good candidate for black-and-white.....:)

Julie, I see you made it disappear in LR. What settings did you use?

[JulieM]

Chuck,

I moved the green, aqua, blue, and purple all the way to the left and I don't detect any more fringing. I've posted that version in my 366 blog (link in my signature).

It does look good treated with various black and white formulations. But, I really like the color of the light on the statue and didn't want to lose it...

Thanks for pondering this one. If you have any other ideas about it I'd love to hear them...