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Author Topic: Chromatic aberration in ACR  (Read 14341 times)
cocasana
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« on: June 24, 2008, 10:13:22 AM »
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Hi there,
I'm probably doing something wrong (it doesn't look that difficult) but I'm never really satisfied on how the Chromatic Aberration tool works in ACR.
Am I the only one that thinks that it could be easily improved?
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Schewe
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« Reply #1 on: June 24, 2008, 10:17:16 AM »
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If you zoom into 200-400% at the corners, you should be able to remove CA pretty easy. You could make a preset to be used with a given lens but it will change based on subject distance and F stop and in the case of zooms, the zoom setting. If you think CA could be improved, feel free to post a feature request at the Camera Raw forum at the Adobe User to User forums...note however, it would be useful to already know how to use the current tool to its fullest before asking for improvements.
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walter.sk
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« Reply #2 on: June 24, 2008, 10:30:51 AM »
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I think the implementation in ACR is very good, but I also believe that there are inherent limitations to how well the chromatic aberration can be corrected.

Often, even at 400% zoom, you can find that when you correct an image using both sliders (with the help of the Alt-key) you might find that some CA then shows in a different area, often nearby.  For example, if you correct the horizontal and vertical CA on the corner of a building, a nearby diagonal might now show problems.

I'm not sure that the CA is linear, if that is the term to use here, but you are in effect resizing one or two channels relative to the third and to each other.

I'm just thrilled to have a way to improve the CA at the RAW stage.  Years ago it was a case of desaturating and/or cloning to reduce the effect of CA.
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cocasana
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« Reply #3 on: June 24, 2008, 10:41:01 AM »
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If you zoom into 200-400% at the corners, you should be able to remove CA pretty easy. You could make a preset to be used with a given lens but it will change based on subject distance and F stop and in the case of zooms, the zoom setting. If you think CA could be improved, feel free to post a feature request at the Camera Raw forum at the Adobe User to User forums...note however, it would be useful to already know how to use the current tool to its fullest before asking for improvements.
[a href=\"index.php?act=findpost&pid=203363\"][{POST_SNAPBACK}][/a]

Hi Jeff, thank you for your quick reply. You don't know me, but I know you (please consider me a fan of yours). its a long time  I've been following your work on the web.
This morning I've looked again the episode in which you are speaking of CA in the "The Luminous Landscape Guide to Adobe Camera Raw", but in many cases it seems I can't achieve total remove of CA in some of my photos. Something red or blue or cyan remains here and there.
Please be sure I wouldn't/wont ask for improvements without being more then absolutely sure (never happens to me) to know everything on CA!
My kindest regards,
Carlo

Thanks Walter, you wrote while I was writeing his msg!
« Last Edit: June 25, 2008, 02:17:10 AM by cocasana » Logged
Misirlou
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« Reply #4 on: June 24, 2008, 10:44:06 AM »
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I tend to fuss around quite a bit in LR, trying to adjust the CA sliders to completely remove the CA from the most important parts of the image. But to be honest, I'm not sure that I'm actually making much of a difference in prints with that.

The automated CA removal in DXO does a great job, and apparently corrects for non-linear effects, but even DXO's not perfect. Sometimes there are still a few colored fringes in some images when viewed at high magnification (usually associated with specular highlights). Again, I'm not sure that CA remainder would ever show up in a print.
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Schewe
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« Reply #5 on: June 24, 2008, 12:02:48 PM »
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This morning I've looked again the episode in which you are speaking of CA in the "The Luminous Landscape Guide to Adobe Camera Raw", but in many cases it seems I can't achieve total remove of CA in some of my photos.
[a href=\"index.php?act=findpost&pid=203370\"][{POST_SNAPBACK}][/a]


You need to understand the difference between chromatic aberration and fringing caused by the demosiacing process. In the Lens Corrections panel there are drop downs for both Highlight Defringe as well as All Edges...combining CA with either Highlights or all edges should remove any noticable fringing at 200-400% and if it doesn't completely remove it it will mitigate it to the point where it's visually unimportant.
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cocasana
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« Reply #6 on: June 24, 2008, 12:55:36 PM »
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You need to understand the difference between chromatic aberration and fringing caused by the demosiacing process. In the Lens Corrections panel there are drop downs for both Highlight Defringe as well as All Edges...combining CA with either Highlights or all edges should remove any noticable fringing at 200-400% and if it doesn't completely remove it it will mitigate it to the point where it's visually unimportant.
[a href=\"index.php?act=findpost&pid=203388\"][{POST_SNAPBACK}][/a]

Actually that' the way I normally proceed. But sometimes I'm tempted to select CA in a saturation layer and mask it away...
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NikoJorj
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« Reply #7 on: June 25, 2008, 07:42:03 AM »
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I think the implementation in ACR is very good, but I also believe that there are inherent limitations to how well the chromatic aberration can be corrected. [...] For example, if you correct the horizontal and vertical CA on the corner of a building, a nearby diagonal might now show problems.
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If I may throw in my 2c's (more than 3 for actually as they're from Europe  )... I hope I won't state too much of the obvious, sorry if it's the case!

First - it goes without saying, but I'd better say it - there are 2 more potential culprits than the 'usual suspect' Transverse Chromatic Aberration : Longitudinal Chromatic Aberration, and fringing around specular highlights due to demosaicing as said Jeff.
For the 2 types of CA, evereybody knows [a href=\"http://www.vanwalree.com/optics/chromatic.html]van Walree's site[/url] I assume?
Fringing and LCA are (first order) constant across the frame whereas TCA is radial (ie zero at center, max in the corners), so the remedy for the latter won't cure the formers - which are what the Defringe dropdown is made for, or am i wrong?

Second, and maybe it's where the ACR CA tool could be marginally improved, the TCA is not always linear across the frame but sometimes quite complex - see for an example the graphs of DPR's lens tests.

But I'm essentially talking for others here - my only lens showing significant CA is the EFS 10-22, and dialing something like -17/+17 I don't see much of it anymore (works more or less for the entire focal/diaph range, life's good).
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Nicolas from Grenoble
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« Reply #8 on: June 29, 2008, 12:58:15 AM »
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I am not much an user of ACR (I prefer a different converter) but I must say that ACR and Lightroom are the best of the bunch for CA and fringing,  for ease of use, speed and effective removal.

The worst CA I have is with the Canon 10-22 for the 20D at 10mm, but also the 17-40 L and the 24-105 L for the 5D have CA at widest angle, quite visible annoying if not corrected in prints bigger than A4.

I don't do any pixel peeping at 200% on screen, but I do print up to A2+ with my Epson 3800. For critical CA cases I use ACR and defringing on Tiffs out of the converter of my choice.
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Robin Balas
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« Reply #9 on: July 05, 2008, 10:05:52 AM »
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If you zoom into 200-400% at the corners, you should be able to remove CA pretty easy. You could make a preset to be used with a given lens but it will change based on subject distance and F stop and in the case of zooms, the zoom setting. If you think CA could be improved, feel free to post a feature request at the Camera Raw forum at the Adobe User to User forums...note however, it would be useful to already know how to use the current tool to its fullest before asking for improvements.
[a href=\"index.php?act=findpost&pid=203363\"][{POST_SNAPBACK}][/a]

Personally I find the CA tools in ACR to be terrific for normal use, but I struggle with my TS-E lenses and the strange russian 45mm for my MFDB as they do have quite alot of CA and it is way off center when shifted. I realize it is a bit special, but having the means to set the CA correction center away from the image file's center would make my day and other users of shift lenses.
Today I make to versions for CA removal one left or right (if I shifted left and right) and manually blend the two frames. But this is no good solution as the CA is very non-linear when shifts and tilts is used.
So 3 sliders is needed in addition, offset distanse from center, offset angle and a linear to very non-linear CA from center to corner. And showing 4 small preview boxes simultaneously in 400% of each corner (movable ones) will dramatically speed up the CA removal process as today I have to scroll around in 400% which takes some time in huge files. Also quite a few compacts capable of RAW have non-centered chips and a offset possibility would fix all those.

I'm not familiar with the adobe forums so if anyone could either provide a direct link or refer this thread to them I would be greatfull. CA removal is very important for my work (food and other studio built product environments) as I use shifts and tilts extensivly and waiting with CA to after the de-bayer is way to slow for me, i.e. using the lens distortion filter and adding in a empty space in the files to compensate for the shifts and put the CA ceter in the image file center.
MHO.
Robin Balas
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[span style='font-family:Arial']Robin Balas
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dfphoto
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« Reply #10 on: July 24, 2008, 10:45:24 AM »
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Hi I'm a digital tech in Los Angeles, I've seen at least 500k images from a variety of camera companies, CA usually starts with the camera and lenís combo you're using. You'd be surprised at how many lenses and camera bodies are slightly out of alignment and causing CA. Add the lower end lenses, 3rd party lenses and finally add the critical tolerance digital needs and you have CA. Adobe does a good job but not perfect, I've sent in my rental Canon camera and it was drastically improved once it returned. (send lens and body in) Camera Raw will not solve all issues, but it will solve many issues; you can't expect a 200.00 software to fix a manufacturing issue.

Thanks David
« Last Edit: July 24, 2008, 10:47:54 AM by dfphoto » Logged
Robin Balas
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« Reply #11 on: July 25, 2008, 04:11:18 PM »
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Hi I'm a digital tech in Los Angeles, I've seen at least 500k images from a variety of camera companies, CA usually starts with the camera and lenís combo you're using. You'd be surprised at how many lenses and camera bodies are slightly out of alignment and causing CA. Add the lower end lenses, 3rd party lenses and finally add the critical tolerance digital needs and you have CA. Adobe does a good job but not perfect, I've sent in my rental Canon camera and it was drastically improved once it returned. (send lens and body in) Camera Raw will not solve all issues, but it will solve many issues; you can't expect a 200.00 software to fix a manufacturing issue.

Thanks David
[a href=\"index.php?act=findpost&pid=210436\"][{POST_SNAPBACK}][/a]

CA is not my problem - non-centred CA from shift (and also sometimes from tilts) capable lenses is my main problem today. As I wrote I have a workaround, but it is slow and cumbersome. Camera body alignment is not the issue here. Neither is re-collimating the lenses. The issue is that the optical centre is not in the image centre and ACR has no means to accommodate that.
the price of the software has nothing to do with it, is there anything more capable on the market regardless of price without seriously messing up something else?
MHO.
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[span style='font-family:Arial']Robin Balas
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bjanes
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« Reply #12 on: July 25, 2008, 06:25:39 PM »
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You need to understand the difference between chromatic aberration and fringing caused by the demosiacing process. In the Lens Corrections panel there are drop downs for both Highlight Defringe as well as All Edges...combining CA with either Highlights or all edges should remove any noticable fringing at 200-400% and if it doesn't completely remove it it will mitigate it to the point where it's visually unimportant.
[{POST_SNAPBACK}][/a]

It is nice to learn about the use of the defringe function in Photoshop to remove fringing caused by demosaicing.

There are two types of chromatic aberration: [a href=\"http://www.vanwalree.com/optics/chromatic.html]Longitudinal and Transverse[/url]. Transverse chromatic aberration (also called lateral) causes color fringing resulting from a difference in the magnification at different wavelengths of light.  I think that only this type of chromatic aberration can be removed by Camera Raw and other programs.

Longitudinal chromatic aberration causes different wavelengths to focus on different image planes. It causes a degradation of MTF response-- by differing amounts for different colors. (see here).

With some dedicated raw converters such as Nikon Capture, the lens in use can be determined from the metadata and the appropriate correction for chromatic aberration can be done automatically. Of course, this works only with Nikon lenses.

With the D3, there is some algorithm in the camera to read that amount of lateral color and do correction automatically with in camera JPEGs. With raw, the necessary data can be recorded as metadata and the correction done by Nikon Capture. This works for all lenses, not just Nikkors.

If you use Nikon and have a lens with bothersome chromatic aberration, Nikon Capture is useful even though I usually use ACR.

Bill
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madmanchan
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« Reply #13 on: July 25, 2008, 08:26:35 PM »
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Mild cases of axial (longitudinal) CA can be removed or at least reduced by CR's Defringe option.
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ErikKaffehr
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« Reply #14 on: July 25, 2008, 11:15:07 PM »
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Hi,

I see your point with lens shift. Your suggestions are sound and I hope Adobe will listen. While they listen I think they should really add distortion correction and even perspective correction in ACR and Lightroom.

Best regards
Erik

Quote
Personally I find the CA tools in ACR to be terrific for normal use, but I struggle with my TS-E lenses and the strange russian 45mm for my MFDB as they do have quite alot of CA and it is way off center when shifted. I realize it is a bit special, but having the means to set the CA correction center away from the image file's center would make my day and other users of shift lenses.
Today I make to versions for CA removal one left or right (if I shifted left and right) and manually blend the two frames. But this is no good solution as the CA is very non-linear when shifts and tilts is used.
So 3 sliders is needed in addition, offset distanse from center, offset angle and a linear to very non-linear CA from center to corner. And showing 4 small preview boxes simultaneously in 400% of each corner (movable ones) will dramatically speed up the CA removal process as today I have to scroll around in 400% which takes some time in huge files. Also quite a few compacts capable of RAW have non-centered chips and a offset possibility would fix all those.

I'm not familiar with the adobe forums so if anyone could either provide a direct link or refer this thread to them I would be greatfull. CA removal is very important for my work (food and other studio built product environments) as I use shifts and tilts extensivly and waiting with CA to after the de-bayer is way to slow for me, i.e. using the lens distortion filter and adding in a empty space in the files to compensate for the shifts and put the CA ceter in the image file center.
MHO.
Robin Balas
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ErikKaffehr
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« Reply #15 on: July 25, 2008, 11:16:32 PM »
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Thanks for the suggestion, Eric.

Best regards
Erik

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Mild cases of axial (longitudinal) CA can be removed or at least reduced by CR's Defringe option.
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rdonson
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« Reply #16 on: July 28, 2008, 05:39:42 PM »
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Hi,

I see your point with lens shift. Your suggestions are sound and I hope Adobe will listen. While they listen I think they should really add distortion correction and even perspective correction in ACR and Lightroom.

Best regards
Erik
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Why wait?  Check out [a href=\"http://epaperpress.com/ptlens/]PTLens.[/url]  One of the best bargains in digital photography.
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[span style='font-size:14pt;line-height:100%'][span style='font-family:Arial'][span style='font-family:Geneva'][span style='font-size:8pt;line-height:100%']Regards,
Ron[/span][/span][/span][/span]
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