Purple Fringing on Oly and Pany Bodies: Causes and Remedies

Started Jun 7, 2013 | Discussions
Anders W Forum Pro • Posts: 21,466
Purple Fringing on Oly and Pany Bodies: Causes and Remedies
10

As many forum members are already aware, images produced with MFT equipment sometimes show so-called purple fringing (PF). In some respects, this is not a phenomenon specific to MFT but one that can appear with any camera system. One example, caused by longitudingal chromatic aberration (LoCA), is PF in the out-of-focus area along contrast edges of objects closer to the camera than those in focus. Another example, again caused by LoCA, is PF in the in-focus area when fast lenses are used at wide apertures. This second type of PF, however, is not very common with native MFT lenses since most of them are well corrected optically in this regard.

However, there are also some manifestations of PF that are possibly more MFT-specific. To begin with, Panasonic lenses are designed to be software-corrected for lateral chromatic aberration (LaCA). When such lenses are used on Olympus bodies, the software correction for which the lenses are designed is not carried out, which can result in rather prominent purple or magenta fringes on one side of an object and green fringes on the other. Even some Olympus lenses can show quite a bit of this phenomenon in spite of the fact that they are presumably designed to be optically corrected for LaCA (since no Olympus body autocorrects for the problem, no matter which lens is used).

Now this problem can be solved by using a RAW converter (or other PP tool) that can correct for LaCA, such as Lightroom (LR) 4.x, which contains a checkbox labeled "Remove Chromatic Aberration" intended for that purpose. As at least some of us have observed, however, checking this box does not always remove the fringing completely. The green fringe is gone but some of the purple remains and can only be eliminated by other means, such as the defringe tool of LR 4.x, whose presence is certainly welcome but whose use is not completely free from downsides.

This residual PF is a bit mystical in several respects. First, it appears on one side of an object only, not both sides as would be expected if it were caused by LoCA. Second, it is more prominent at the edges of the frame than in the center, not equally prominent everywhere as would be expected if it were due to LoCA. Finally, it is only marginally reduced by stopping down, not strongly so as would be expectued if LoCA were the culprit. So what's actually going on here?

Below I show five 100 percent crops, all from images shot with the Pansonic 20/1.7 wide open and all processed by means of LR 4.4.

The first is shot with the G1. This means that LR corrects the LaCA regardless of whether its LaCA box is checked or not. As you can see, there are hardly any traces of PF in this case.

The second and third crop are both from the same E-M5 image, just processed differently. The LaCA box was left unchecked for the first of the two but checked for the second. As you can see, the residual PF is in this case quite prominent, not only when the box is left unchecked but also when it is checked.

The two last crops are again from the same E-M5 image, just processed differently in the same way as the previous pair. The image used, however, is not identical to the one used for the previous pair. As you can see, the residual PF is in this case far less prominent. With the LaCA box checked, the result is now nearly as free from PF as the crop from the G1 image.

Before I try to explain what's going on here, a little guessing game: What is the reason why the E-M5 leaves residual PF even when LaCA is corrected while the G1 doesn't, what "secret anti-PF weapon" did I use to pretty much eliminate that residual PF, and what explains its effect?

Everyone is free to guess except "secretworld" who, as his nick suggests, has privileged information on all the secrets of the world.

Crop 1: G1

Crop 2: E-M5, LaCA box unchecked

Crop 3: E-M5, LaCA box checked

Crop 4: E-M5 with "secret anti-PF weapon" and LaCA box unchecked

Crop 5: E-M5 with "secret anti-PF weapon" and LaCA box checked

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Laszlo13
Laszlo13 Contributing Member • Posts: 883
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

Anders - I have no idea, but just wanted to add that I purchased DxO Optics Pro for this very specific reason (I user Aperture otherwise) - and it does a reasonable job automatically.  But it too tends to leave just a bit of PF behind.

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Laszlo13
Laszlo13 Contributing Member • Posts: 883
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

Anders - could you share the original OM-D file?  I would love to try it in DxO Pro - to see what happens.  I couldn't download it from the link.

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dotborg Veteran Member • Posts: 8,251
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

It's because your raw converter simply doesn't do as good of a job as your G1 does in-camera.

Try RawThreapee and see if it does a better job for you.

Digital Dick Senior Member • Posts: 1,673
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

It's a very easy fix in Lightroom

Dick

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Laszlo13
Laszlo13 Contributing Member • Posts: 883
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

Well - without the original file, DXO struggled a bit.  The exif information is missing the lens information, plus it's a low res image.  As such - it still almost removed all CA - save for a small section.

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Laszlo13
Laszlo13 Contributing Member • Posts: 883
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

Strange - the image isn't coming up, unless you click on it?

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texinwien Veteran Member • Posts: 3,326
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

Any relation to the solution to the Panasonic 7-14mm & OMD EM5 purple flare problem you figured out?

Looking forward to the answer. I fly out on vacation Sunday night, so tomorrow morning is my last chance to buy gear before I leave

Dunno what the camera shops in Sri Lanka are like, but I'm guessing they're not that great.

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Alumna Gorp Senior Member • Posts: 1,531
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

I tried my Pany 14mm on the OMD and tried to capture some CA, there was a whole lot less than I was expecting, and what little was there was easily removed in LR using the sliders.

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OP Anders W Forum Pro • Posts: 21,466
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

texinwien wrote:

Any relation to the solution to the Panasonic 7-14mm & OMD EM5 purple flare problem you figured out?

Not such a bad guess tex. As a matter of fact, the explanation/solution I have now come across is at least in part a by-product of our go-around with "Mr. Fish" in this thread

http://www.dpreview.com/forums/post/51541995

a little while ago although the credit for making the observation that put me on the right track is, as that post reveals, certainly not his.

Ironically, this phenomenon (residual PF that in some important ways behaves like LaCA rather than LoCA) is one that I observed, and was puzzled by, already before the problem with purple flare with the 7-14 on the E-M5 surfaced. And in both cases, I was on the right track early on but incorrectly rejected the hypothesis due to not having/using quite the right equipment, as you can see here:

http://www.dpreview.com/forums/post/50380384

Looking forward to the answer. I fly out on vacation Sunday night, so tomorrow morning is my last chance to buy gear before I leave

So hurry up to that well-supplied camera store I am sure you have around the corner and ask them to replace the UV/IR-cut filter on the sensor on your E-M5 with its counterpart from the GH3 (which I think has quite the right size to fit ). If, against all odds, that would fail, just ask them to pick up one of those Wratten 2A or Wratten 2E gels I am sure they have laying around in a drawer somewhere since the last time someone asked about them 20 or so years ago. Then pick up some thin double-adhesive from the hardware store next door and you are all set to go.  

Dunno what the camera shops in Sri Lanka are like, but I'm guessing they're not that great.

Could conceivably be that they are not quite as well equipped as those in Vienna, but this is easy-peasy stuff so surely no problem.

Personally, I might have better luck. Flying out to LA on Wednesday for a trip to the Sierras together with my wife, our son, and our daughter-in-law. Possibly, I'll have to time to pass by Samy's and pick up one of those Wratten 2Es I see they have in stock. Good price too. Only 24.59 for a 3x3 sheet.

 Anders W's gear list:Anders W's gear list
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OP Anders W Forum Pro • Posts: 21,466
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

dotborg wrote:

It's because your raw converter simply doesn't do as good of a job as your G1 does in-camera.

Not quite. It's because no RAW converter can do as good a job with this as my G1 does in-camera. Have a look here for more info of what this is actually about if you are interested:

http://www.dpreview.com/forums/post/51604390

Try RawThreapee and see if it does a better job for you.

I am sure it wouldn't.

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cmpatti Regular Member • Posts: 254
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

If, against all odds, that would fail, just ask them to pick up one of those Wratten 2A or Wratten 2E gels I am sure they have laying around in a drawer somewhere since the last time

someone asked about them 20 or so years ago.

Exactly what I did.  Charged me $5 for the 3x3 inch gel.  Probably the price tag that got stuck on there in the 90's.  7-14 works fine now.

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walkaround Senior Member • Posts: 2,551
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

Anders W wrote:

texinwien wrote:

Any relation to the solution to the Panasonic 7-14mm & OMD EM5 purple flare problem you figured out?

Not such a bad guess tex. As a matter of fact, the explanation/solution I have now come across is at least in part a by-product of our go-around with "Mr. Fish" in this thread

http://www.dpreview.com/forums/post/51541995

a little while ago although the credit for making the observation that put me on the right track is, as that post reveals, certainly not his.

Ironically, this phenomenon (residual PF that in some important ways behaves like LaCA rather than LoCA) is one that I observed, and was puzzled by, already before the problem with purple flare with the 7-14 on the E-M5 surfaced. And in both cases, I was on the right track early on but incorrectly rejected the hypothesis due to not having/using quite the right equipment, as you can see here:

http://www.dpreview.com/forums/post/50380384

Looking forward to the answer. I fly out on vacation Sunday night, so tomorrow morning is my last chance to buy gear before I leave

So hurry up to that well-supplied camera store I am sure you have around the corner and ask them to replace the UV/IR-cut filter on the sensor on your E-M5 with its counterpart from the GH3 (which I think has quite the right size to fit ). If, against all odds, that would fail, just ask them to pick up one of those Wratten 2A or Wratten 2E gels I am sure they have laying around in a drawer somewhere since the last time someone asked about them 20 or so years ago. Then pick up some thin double-adhesive from the hardware store next door and you are all set to go.  

Dunno what the camera shops in Sri Lanka are like, but I'm guessing they're not that great.

Could conceivably be that they are not quite as well equipped as those in Vienna, but this is easy-peasy stuff so surely no problem.

Personally, I might have better luck. Flying out to LA on Wednesday for a trip to the Sierras together with my wife, our son, and our daughter-in-law. Possibly, I'll have to time to pass by Samy's and pick up one of those Wratten 2Es I see they have in stock. Good price too. Only 24.59 for a 3x3 sheet.

I'm a little slow... are you taping a pale yellow filter gel to the rear lens element?

OP Anders W Forum Pro • Posts: 21,466
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

Laszlo13 wrote:

Well - without the original file, DXO struggled a bit.  The exif information is missing the lens information, plus it's a low res image.

The lens info is in the EXIF all right. However, DxO most likely doesn't have a lens profile for this lens since, based on the info on their site, they haven't tested it.

As such - it still almost removed all CA - save for a small section.

I guess you used the DxO checkbox labeled "purple fringing" (along, possibly with manual correction of lateral CA). Is this correct?

And yes, it almost removed the residual PF but not quite. Unfortunately, it simultaneously took away all the color of the flowers and miscolored the upper part of the red fence just below the flowers. As I pointed out in my OP, you can use various tools that relies on desaturation (such as the defringe tool in LR) to do the same. But as your example illustrates, these tools have their drawbacks. Further, as shown in this post, it seems that LR can do a better job in this particular case.

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OP Anders W Forum Pro • Posts: 21,466
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

Digital Dick wrote:

It's a very easy fix in Lightroom

Sure. As I mentioned already in my OP, you can rid of the remaining PF by means of the LR defringe tool. But as I additionally pointed out, that tool has its drawbacks, as do all tools based on the idea of simply desaturating the offending hues. You have to be careful to set the sliders so as desaturate exactly what you want to desaturate and nothing else (and you did a good job with that in this case). As pointed out in another post here  you might easily desaturate in places where you wouldn't want to.

Furthermore, it is in qute a few cases impossible to completely get rid of all the PF with the defringe tool without harmful side effects somewhere in the image, no matter how you set the sliders. In that case, you'll have to accept half-baked results or work with the LR brush tool to selectively protect certain areas of the frame from the side-effects caused by defringing.

Checking for harmful side-effects and taking action to eliminate them when present is time-consuming. On top of that, the defringe tool can only replace the purple fringe with a gray/white one. It can neither restore the color that should have been there in the first place, nor restore the correct luminance value. For these reasons, a solution that eliminates the problem already at the time of capture is of course preferable.

Dick

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OP Anders W Forum Pro • Posts: 21,466
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

cmpatti wrote:

If, against all odds, that would fail, just ask them to pick up one of those Wratten 2A or Wratten 2E gels I am sure they have laying around in a drawer somewhere since the last time

someone asked about them 20 or so years ago.

Exactly what I did.  Charged me $5 for the 3x3 inch gel.  Probably the price tag that got stuck on there in the 90's.  7-14 works fine now.

Glad to hear you are making use of my solution to get rid of the purple flare (and as it turns out, the PF too) with the 7-14 and that it works as well for you as it does for me.

That was an extremely good price for a 3x3 inch gel. Did you actually come across some left-over supplies somewhere or what?

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OP Anders W Forum Pro • Posts: 21,466
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

walkaround wrote:

Anders W wrote:

texinwien wrote:

Any relation to the solution to the Panasonic 7-14mm & OMD EM5 purple flare problem you figured out?

Not such a bad guess tex. As a matter of fact, the explanation/solution I have now come across is at least in part a by-product of our go-around with "Mr. Fish" in this thread

http://www.dpreview.com/forums/post/51541995

a little while ago although the credit for making the observation that put me on the right track is, as that post reveals, certainly not his.

Ironically, this phenomenon (residual PF that in some important ways behaves like LaCA rather than LoCA) is one that I observed, and was puzzled by, already before the problem with purple flare with the 7-14 on the E-M5 surfaced. And in both cases, I was on the right track early on but incorrectly rejected the hypothesis due to not having/using quite the right equipment, as you can see here:

http://www.dpreview.com/forums/post/50380384

Looking forward to the answer. I fly out on vacation Sunday night, so tomorrow morning is my last chance to buy gear before I leave

So hurry up to that well-supplied camera store I am sure you have around the corner and ask them to replace the UV/IR-cut filter on the sensor on your E-M5 with its counterpart from the GH3 (which I think has quite the right size to fit ). If, against all odds, that would fail, just ask them to pick up one of those Wratten 2A or Wratten 2E gels I am sure they have laying around in a drawer somewhere since the last time someone asked about them 20 or so years ago. Then pick up some thin double-adhesive from the hardware store next door and you are all set to go.  

Dunno what the camera shops in Sri Lanka are like, but I'm guessing they're not that great.

Could conceivably be that they are not quite as well equipped as those in Vienna, but this is easy-peasy stuff so surely no problem.

Personally, I might have better luck. Flying out to LA on Wednesday for a trip to the Sierras together with my wife, our son, and our daughter-in-law. Possibly, I'll have to time to pass by Samy's and pick up one of those Wratten 2Es I see they have in stock. Good price too. Only 24.59 for a 3x3 sheet.

I'm a little slow... are you taping a pale yellow filter gel to the rear lens element?

That's what I originally did with my 7-14 before I implemented the alternative solution shown here . For the purpose of the sample images in this thread, I simply held the same type of filter (Wratten 2A) in front of the lens in order to study its effect on the PF.

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OP Anders W Forum Pro • Posts: 21,466
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

Alumna Gorp wrote:

I tried my Pany 14mm on the OMD and tried to capture some CA, there was a whole lot less than I was expecting,

The 14 has at least as much of the problem I am illustrating as the 20. However, how much of it you see is strongly scene dependent. Here I picked a scene where it is maximally visible: Intensely white bars against a nearly black backgroud.

You find some good illustrations (although not quite as intense as the one I use in this thread) of how this works out with the 14 here

http://www.dpreview.com/forums/post/50176940

and here

http://www.dpreview.com/forums/post/50380384

and what little was there was easily removed in LR using the sliders.

As I pointed out in my OP, you can remove it with the LR defringe tool all right but there are downsides to that solution. You find a description of those downsides here

http://www.dpreview.com/forums/post/51604539

and an illustration here

http://www.dpreview.com/forums/post/51604472

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Laszlo13
Laszlo13 Contributing Member • Posts: 883
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

Anders W wrote:

walkaround wrote:

Anders W wrote:

texinwien wrote:

Any relation to the solution to the Panasonic 7-14mm & OMD EM5 purple flare problem you figured out?

Not such a bad guess tex. As a matter of fact, the explanation/solution I have now come across is at least in part a by-product of our go-around with "Mr. Fish" in this thread

http://www.dpreview.com/forums/post/51541995

a little while ago although the credit for making the observation that put me on the right track is, as that post reveals, certainly not his.

Ironically, this phenomenon (residual PF that in some important ways behaves like LaCA rather than LoCA) is one that I observed, and was puzzled by, already before the problem with purple flare with the 7-14 on the E-M5 surfaced. And in both cases, I was on the right track early on but incorrectly rejected the hypothesis due to not having/using quite the right equipment, as you can see here:

http://www.dpreview.com/forums/post/50380384

Looking forward to the answer. I fly out on vacation Sunday night, so tomorrow morning is my last chance to buy gear before I leave

So hurry up to that well-supplied camera store I am sure you have around the corner and ask them to replace the UV/IR-cut filter on the sensor on your E-M5 with its counterpart from the GH3 (which I think has quite the right size to fit ). If, against all odds, that would fail, just ask them to pick up one of those Wratten 2A or Wratten 2E gels I am sure they have laying around in a drawer somewhere since the last time someone asked about them 20 or so years ago. Then pick up some thin double-adhesive from the hardware store next door and you are all set to go.  

Dunno what the camera shops in Sri Lanka are like, but I'm guessing they're not that great.

Could conceivably be that they are not quite as well equipped as those in Vienna, but this is easy-peasy stuff so surely no problem.

Personally, I might have better luck. Flying out to LA on Wednesday for a trip to the Sierras together with my wife, our son, and our daughter-in-law. Possibly, I'll have to time to pass by Samy's and pick up one of those Wratten 2Es I see they have in stock. Good price too. Only 24.59 for a 3x3 sheet.

I'm a little slow... are you taping a pale yellow filter gel to the rear lens element?

That's what I originally did with my 7-14 before I implemented the alternative solution shown here . For the purpose of the sample images in this thread, I simply held the same type of filter (Wratten 2A) in front of the lens in order to study its effect on the PF.

Great thread.  So - what's the downside of using the 2A filters, on color digital images?  I imagine it helps with contrast as well, but any effect on purple colors?

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cmpatti Regular Member • Posts: 254
Re: Purple Fringing on Oly and Pany Bodies: Causes and Remedies

Anders W wrote:

cmpatti wrote:

If, against all odds, that would fail, just ask them to pick up one of those Wratten 2A or Wratten 2E gels I am sure they have laying around in a drawer somewhere since the last time

someone asked about them 20 or so years ago.

Exactly what I did.  Charged me $5 for the 3x3 inch gel.  Probably the price tag that got stuck on there in the 90's.  7-14 works fine now.

Glad to hear you are making use of my solution to get rid of the purple flare (and as it turns out, the PF too) with the 7-14 and that it works as well for you as it does for me.

That was an extremely good price for a 3x3 inch gel. Did you actually come across some left-over supplies somewhere or what?

I guess that was it.  I walked into my local camera store and aksed whether they had a Wratten 2A, expecting they wouldn't.  Someone went to the back room and rooted through a box to find it.  When they said it would cost only $5, I kept my mouth shut.

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