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02-22-2012, 04:50 PM   #16
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QuoteOriginally posted by Sperdynamite Quote
It's pretty bad. I know I could just stop down but is there a way to get rid of this in post? I use it as a portrait lens for weddings and I'm in a lot of back lit situations...
Shoot RAW and use RAW Therapee.
It has very good CA/PF modules(if not the best) and it's free.
There is also a 20 second Photoshop trick you can do to remove CA/PF which is often used for final retouching.

02-22-2012, 04:57 PM   #17
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QuoteOriginally posted by Lowell Goudge Quote
true Purple Fringing is a digital only issue
From what I remember, there were lots of PF confusing when digital was still young. Then a few websites tried to pin it down with sensor blooming. However, IMHO, this view is too narrow because purple colour fringing isn't caused by sensor blooming alone. Lens CA can be purple in colour too, or green, or red.
02-22-2012, 05:04 PM   #18
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QuoteOriginally posted by wlachan Quote
From what I remember, there were lots of PF confusing when digital was still young. Then a few websites tried to pin it down with sensor blooming. However, IMHO, this view is too narrow because purple colour fringing isn't caused by sensor blooming alone. Lens CA can be purple in colour too, or green, or red.
Yes lens CA can be purple, but it presents itself differently. True PF from sensor blooming is quite different than CA and is only present at extreme bright to dark transitions. cA is there all the time.
02-22-2012, 06:57 PM   #19
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Great explanations - but ......

Many thanks to all of you who have provided explanations of what purple fringing is and how it happens and how to avoid it - but --- if you do have an image with this affliction , what do you do in Lightroom or Photoshop to fix it?

02-22-2012, 06:58 PM   #20
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LR is quite effective on removing CA.
02-22-2012, 07:19 PM   #21
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Maybe this belongs to another Forum section - but ---

QuoteOriginally posted by JohnBee Quote
Shoot RAW and use RAW Therapee.
It has very good CA/PF modules(if not the best) and it's free.
There is also a 20 second Photoshop trick you can do to remove CA/PF which is often used for final retouching.
Would you mind pointing me in the direction of the Photoshop trick?
Thanks
02-22-2012, 07:30 PM   #22
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Although not photo shop, I use PSP X4 which has purple fringe removal and also CA removal, but note not all CA removal tools are created equal. I did an evaluation about 6 months ago where I posted a raw image with very bad lateral CA and let forum members use their tools on it. For plane of focus lateral CA you want a tool that rescales the layers as this improves edge sharpness, for out of focus regions you want a fringe removal tool that you can select the colors and the range of fringing, in terms of pixels to remove what you want
02-22-2012, 08:27 PM   #23
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i mostly just use the chromatic aberration sliders in the lens corrections tab of ACR, do you have this? it makes it easy to shift out those colored fringes. alternatively, i pull down the purple saturation slider (also in ACR), sometimes the cyan one. in the past i would slowly decolorize the fringe with the sponge tool - too tedious but good if the other methods are not practical. i have also used the color sample tool to remove the offending color in a duplicate layer and then painted back in the affected with unaffected areas. i have a few more but that should do.

02-22-2012, 09:39 PM   #24
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QuoteOriginally posted by Lowell Goudge Quote
Yes with CA youo see all "fringing" especially in the out of focus zones.

But the fringing you see is not purple fringing there is a better example posted you see CA and this would be present on film as well as digital, true Purple Fringing is a digital only issue
I call the car sample "purple blooming" Others call it sensor blooming. But if you check the wikipedia article on purple fringing you will see that the definition is quite generic and the sample provided is not one where purple surrounds a bright spot - it is closer to what wlachan posted.
02-22-2012, 09:43 PM   #25
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QuoteOriginally posted by mikeSF Quote
i mostly just use the chromatic aberration sliders in the lens corrections tab of ACR, do you have this? it makes it easy to shift out those colored fringes. alternatively, i pull down the purple saturation slider (also in ACR), sometimes the cyan one. in the past i would slowly decolorize the fringe with the sponge tool - too tedious but good if the other methods are not practical. i have also used the color sample tool to remove the offending color in a duplicate layer and then painted back in the affected with unaffected areas. i have a few more but that should do.
Thanks, mikeSF. Lens correction doesn't remove purple fringing for me, but reducing Purple saturation does in both Lightroom and Photoshop, it's a pity about the effect on the purple tones in other parts of the picture . I hope that LR4 will make this a bit easier.
02-22-2012, 09:44 PM   #26
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QuoteOriginally posted by Laurentiu Cristofor Quote
I call the car sample "purple blooming" Others call it sensor blooming. But if you check the wikipedia article on purple fringing you will see that the definition is quite generic and the sample provided is not one where purple surrounds a bright spot - it is closer to what wlachan posted.
Except that there is no need to redefine CA as purple fringing. For me, what people talk about purple fringing on digital , they are discussing sensor bloom, because CA has been called CA for fifty years with lenses (at least) with film lenses, you dont need to call it something new just because it is now digital.
02-22-2012, 09:46 PM   #27
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Very nice artiacle about CA and he also talks about PF
http://toothwalker.org/optics/chromatic.html

What most call PF is actually longitudinal chromatic aberration.

And it isn't a sensor thing, at least not for the most part.
If it was then tell me why it does not show up with all the lenses?

Last edited by Anvh; 02-22-2012 at 09:56 PM.
02-22-2012, 09:55 PM   #28
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QuoteOriginally posted by Anvh Quote
Very nice artiacle about CA and he also talks about PF
Chromatic aberrations

What most call PF is actually longitudinal chromatic aberration
But really all the article does is say that all fringing, except sensor bloom is really CA and that is the end of it.
02-22-2012, 10:04 PM   #29
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QuoteOriginally posted by Laurentiu Cristofor Quote
I call the car sample "purple blooming" Others call it sensor blooming. But if you check the wikipedia article on purple fringing you will see that the definition is quite generic and the sample provided is not one where purple surrounds a bright spot - it is closer to what wlachan posted.
Happy to call it whatever - sensor blooming sounds ok to me. It's the removal that's the hard thing to do

If my first attempt at attaching a picture works , you'll see that "purple blooming" applies in 2 ways, where if I remove the unwanted purple edges around the icing, the agapanthus petals on the left are also affected (not that it bothers me in this happy-snappy) ... fyi, the lighting is indirect daylight coming from the south (Australian orientation), so not really backlit.
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02-22-2012, 10:25 PM   #30
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QuoteOriginally posted by Anvh Quote
Very nice artiacle about CA and he also talks about PF
Chromatic aberrations

If it was then tell me why it does not show up with all the lenses?
When I asked Pentax why the 77 Ltd exhibited purple fringing a Pentax technician explained that it was mainly because the FA lenses are optimised for film therefore do not focus the light at exactly the right focal plane because the sensor is much thinner than 35mm film.

I am sorry I cannot remember exactly how he explained it so this explanation may be a bit thin so I hope someone else may be able to explain it in a more technical way.
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