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03/05/2006 08:32:56 AM · #1 |
I've readed that it is possible to minor or correct CA, also callerd purple fringing, in post processing.
I was cataloguing some images and prepare them for stock and I've encountered some problens in what concerns CA.
Here's an example:
 
When you look at the image all toguether it looks ok, but when viewing it at the detal (2º image is a 100% crop) it looks bad.
Any ideas how to correct it in Photoshop or other way, in this image or in others? Any tips are wellcome.
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03/05/2006 08:47:30 AM · #2 |
I took your image into photoshop and the easiest method I could find was:
Using magic wand, select some of the purple.
Use replace color, eyedropper some of the purple part (this limits the color shifted) and shift the hue, add a little saturation, and darken it slightly.
I did this once for the tail, once for the head, and once for the wing using 32 tolerance, contiguous.
You could also clone out the CA.
I tried just desaturating it, which works pretty often, but your purple is in the blue family so it interferred with the background.
Good luck! |
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03/05/2006 08:52:05 AM · #3 |
OH GOSH, I SO understand your plight. I have had this happen to me even on manual settings where I could get the best picture. Still CA shows in some instances. I was told once that if your Fstop is on a 6.0, for example, bringing it to something like an F8 or F9 may help. But for me, this only seems to now render a darker image then wanted. I haven't figured out how to rid of it in PSP, but was also told that giving the entire photo a more magenta hue would help, but then the photo IS overall more magenta, which I don't like either. LOL....I haven't toyed with magic wands much this year and have lost my ability to figure that out now. LOL..I would have to do some searching, but it is quite a problem for me as well, and a HUGE bummer when it happens to great images.
Rose
Message edited by author 2006-03-05 08:53:03. |
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03/05/2006 09:03:53 AM · #4 |
Originally posted by Nuno:
I've readed that it is possible to minor or correct CA, also callerd purple fringing, in post processing. |
If you're googling this problem, just to let you know that CA stands for 'Chromatic Aberration', and not 'Colorcast Aberration'
It's caused by the type of glass in the lens. The different wavelengths of light aren't all focussed on the same spot, so you get blue or red/purple appearing slightly offset. Giving the fringing effect.
More expensive lenses use apochromatic glass (usually made of something like flourite) in specific combinations to correct for this problem.
As for correcting for it in PS? - I generally use the sponge in desaturation mode where possible.
Message edited by author 2006-03-05 09:04:29. |
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03/05/2006 09:05:20 AM · #5 |
Without having to make a selection, you can also open hue/saturation and from the pull-down select "Magentas." Now slide the saturation slider all the way to the left or right temporarily to see what areas will be affected. Now move the color sliders a little and try to get the effect limited to just the fringing; since this color is not commonly found in shots otherwise, it's usually possible; if there's a separate (not connected) object that gets affected, don't worry about it for now. Adjust the saturation to zero, or near there (fully left), then tweak lightness if required. The magenta has now been replaced by neutral gray, which is usually much less noticeable.
Now, if there are any other small areas that got affected, yoiu can reverse the above effect with the history brush if using Photoshop; for PSP, I don't know if there is an equivalent. If not, you'd need to mask off these areas before applying the hue/sat adjustment.
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03/05/2006 09:10:32 AM · #6 |
Good and simple way. Than's kirbic. I'll try it. And thank's jhonan for the correction. My english is not to notch. :)
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03/05/2006 09:23:12 AM · #7 |
Nuno... if you have Photoshop CS2 I have a suggestion you might try I think will work for you.
Here it is:
1-Select Filter->Noise->Noise Reduction
2-Use settings: Strength-6, Preserve Details-100%, Reduce Color Noise 80%, Sharpen Details-0%
I found when comparing CS2's noise reduction to that of Neat Image that CS2 is better at removing color noise but not as good at removing artifacts. ;) It can help your problem.
The settings above apply no noise reduction to the image but a good amount of color noise reduction which handles your color aberration problem nicely.
Message edited by author 2006-03-05 09:33:00.
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03/05/2006 09:27:36 AM · #8 |
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03/05/2006 09:34:00 AM · #9 |
Originally posted by Nuno:
Nope! PS CS only |
Big bummer! Had a solution for you, but good in CS2 only.
What I do now is apply Neat Image for noise reduction and then use CS2 for additional color noise reduction if needed. I prepare images for larger prints and these type of problems become more apparent for larger print sizes.
Message edited by author 2006-03-05 09:37:29.
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