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Thread started 15 Jan 2017 (Sunday) 06:46
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Fixing chromatic abberation - best SW?

 
the ­ hulk
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Jan 15, 2017 06:46 |  #1

I always use Lightroom as editing software for my raw files. A couple of year a go I frequently shoot with Canon 85 f/1.8 wide open resulting in heavy CA in high contrast scenes. Probably the worst Canon lens in regard of CA.

Some of the photos I still really like and I would like to get rid of the CA.

With Lightroom 5 or 6 the CA can be removed completley but insted of the color fringing Lightroom creates a gray colored line several pixels thick. Like a halo around high contrast areas. Easy seen in A3 and bigger prints. Some photos I have been using the cloning tool to copy surrounding pixels instead of the grey ones but this is a very very time consuming way to solve this problem.

Are there other softwares out there that can correct CA better than Lightroom?




  
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chauncey
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Jan 15, 2017 07:19 |  #2

I would investigate your shooting techniques before trying to fix it in post.


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Jan 15, 2017 07:51 |  #3

Getting rid of the unwanted colour is the easy bit, it's the what you do with it afterwards that is really hard. Sometimes I think it might be worth leaving the colour in place and taking it to PS. There you could use the select colour range tool to select the colour created by the finding, which is often quite unique in an image. Once you have it selected hide the marching ants (Ctrl/Cmd-H) so that you have an unobscured view and use the HSL tool (Ctrl/Cmd-U) to adjust away the fringing colour not only by desaturating it, but also by shifting the hue and luminance. This is going to be one of those times when you may well need to use multiple individual colour channels as well as the master mix to get the best results. You might even need to do multiple selections of the fringe colours across the image depending on the background colour behind the finge. You will probably still have lines there, but they would be a lot less visible than the simply desaturated ones. Other than that yes it will probably need the use of the clone stamp tool to cover it up. The spot healing tool now that it allows you to paint with it might be enough, since generally you just want to move the correctly coloured pixels over a bit, which if you work at a high magnification, using a smallish brush with 100% feather in smallish areas should work you will just need to remember that with doing it this way the selected area to clone always has to exactly match the area being cloned in shape and orientation. At least I have never noticed a way to rotate the from area compared to the to area. If you switch off the tool overlay you will be able to overlay applications of the tool much easier, something I wish I had known when working in LR 4, since that didn't allow brushing, and with the tool overlay showing if you try to place the center of a new brush application within the diameter to an existing one it changes the function from add new spot to select existing spot.

Alan


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gjl711
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Jan 15, 2017 08:06 |  #4

I have found that in many instances DPP does a better job with CA than Adobe's products.


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the ­ hulk
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Jan 15, 2017 09:16 |  #5

chauncey wrote in post #18244926 (external link)
I would investigate your shooting techniques before trying to fix it in post.

Nothing too do with shooting technic. Its the lens design. The 85mm is replaced with a 85LII. Much better CA correction for same aperture and high contrast scenes.




  
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rrblint
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Jan 15, 2017 09:58 |  #6

DXO OpticsPro (external link) has excellent CA correction.


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tonylong
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Jan 15, 2017 11:58 |  #7

Interesting, I shot with the wonderful EF 85mm f/1.2L, maybe it's been updated, but I did encounter CA on some shots, Oh Well.

My "fix" was to use the LR CA "tool", but then to resort to the LR Brush set to desaturate the specific color, which typically was purple. That left other colors pretty much "OK", at least for my work!


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Bassat
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Jan 15, 2017 12:48 |  #8

I've been using an EF 85 1.8 for years. The only frame I ever had real CA problems with was one that I downloaded from a review; it was shot specifically to show how bad the lens was with CA. In real life, I've never encountered CA that caused me to bin a shot. I don't pixel peep, though. To me, if it looks good at 8"x10", it looks good.




  
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the ­ hulk
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Jan 15, 2017 13:34 |  #9

Bassat wrote in post #18245141 (external link)
I've been using an EF 85 1.8 for years. The only frame I ever had real CA problems with was one that I downloaded from a review; it was shot specifically to show how bad the lens was with CA. In real life, I've never encountered CA that caused me to bin a shot. I don't pixel peep, though. To me, if it looks good at 8"x10", it looks good.

I dont pixel peep either but print a bit bigger, often A3+.

The 85 f/1.8 is a great lens with excellent optical performance and super fast auto focus but the longitudinal chromatic abberation is very strong. I think its also called purple fringing.

85L also have that but is much better controlled at f/1.8. I dont think it is possible to get rid of that in a fast lens. Apochromatic lens design is the only way to keep it at a low level, like some Zeiss lenses.

The photos I want to correct are backlit flowers in silouettes at sunsets. Actually I had the serie of backlits flowers on display at exihibition. Nobody complained about the CA though but it was clearly visible by me and now I want to get rid of it;-)a




  
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Damo77
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Jan 15, 2017 14:38 |  #10

This (external link) is the method I use in Photoshop, if the raw software lets me down.


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mclaren777
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Jan 15, 2017 16:57 |  #11

the hulk wrote in post #18244907 (external link)
With Lightroom 5 or 6 the CA can be removed completley but insted of the color fringing Lightroom creates a gray colored line several pixels thick.

You need to adjust the sliders in Lightroom after applying CA correction. Typically, you'll want to reduce the overall strength and limit the range of color so it only impacts the CA.


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the ­ hulk
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Jan 16, 2017 01:15 |  #12

mclaren777 wrote in post #18245387 (external link)
You need to adjust the sliders in Lightroom after applying CA correction. Typically, you'll want to reduce the overall strength and limit the range of color so it only impacts the CA.

I always do that but its not enough to reduce the halo effect in this case.

I would like some kind of intelligent tool mix of Lightrooms CA/ColorDefring and the cloning tool. All the colored pixel the defring tool gets rid of the cloning tool should replace the defringed pixels with nearby pixel color in a smooth blending.




  
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BigAl007
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Jan 16, 2017 06:02 |  #13

the hulk wrote in post #18245777 (external link)
I always do that but its not enough to reduce the halo effect in this case.

I would like some kind of intelligent tool mix of Lightrooms CA/ColorDefring and the cloning tool. All the colored pixel the defring tool gets rid of the cloning tool should replace the defringed pixels with nearby pixel color in a smooth blending.


That would be good, but from which side should it clone? Both? Light to dark? Dark to light? Should it clone a strip that is the width of the "line"? or should it just take the very last "good" colour and extend that across? The answer is usually all of the above, and often all in the same image. It is computationally very difficult when dealing with complex two dimensional data arrays, as you in the case of a photograph. It's not too difficult to compute the steps required to draw a single pixel wide line and any arbitrary angle on the grid, although you may need a very long line to see very small differences in angle. It is also pretty trivial to do a two dimensional edge finding routine, and of course we will know where we have changed the colour already. For lines that run along the axes of the array grid it is not too bad, since it becomes quite easy to check that there is no other "line" in close proximity to the pixels that need cloning, if you are going for the full width clone option, and then simply copy x number of pixel values across. This would be the same for cloning from a single side, or both sides. The difficulty is when the "line" of the CA is not parallel to the grid axes of the image array. It becomes quite difficult to calculate the angle from the data, especially with only short runs. The problem is that you need to know the correct angle of the line that was corrected, since it is important that you correctly interpolate the data necessary to make it look like you cloned across orthogonally from the line. Thats just for the parts of the CA that are straight lines, of course that is not always the case, often you will get CA around edges that are actually complex curves. At that point you need to be able to compute your interpolated pixels for cloning based on a line that is orthogonal to the tangent of the curve at that point. That's again not too hard where you calculated the curve in the first place, since a calculation that will deliver up a curve will just as easily give us the tangent at any point along it. calculating the curve from the data is quite tricky, and remember that would be just for one edge of it, most cases of CA are not just a single pixel wide, so you would have to calculate this curve as a two dimensional object, and that adds issues, since the chord length of the inside will be shorter than the chord on the outside of the curved line.

The problems is that computers are actually very poor at seeing patterns in data that humans spot instantly, even when programed by humans! humans are so good at seeing "patterns" that we see them even when they don't really exist. So for a human spotting the corrected areas of CA, and knowing where to clone the data in from is a really simple visual task, and one we are actually very adept at, since spotting irregularities in our field of view has been keeping us alive for millennia. Those who didn't have those skills were weeded out of the gene pool by the simple expedient of becoming dinner for a saber toothed tiger, or some other large, or indeed small, predator. So not only can we easily see the problem, but we can also very easily see where we need to pick up the data to fix the problem, something that is very difficult to program a computer to do. Of course the problem is that for us humans it takes such a long time to do the job by hand. I suppose that as Artificial Intelligence programming improves this will become something that a computer becomes able to manage. It is a bit like catching a ball in the hand, something that most humans are capable of at an instinctive level, we see the ball, and are able to pretty much instantly calculate the flight path, which we can then update based on feedback from out eyes as unseen effects such as the wind change that flight path, then we can control our arm to put our hand in just the right place to catch the ball out of the air. Even a supercomputer on the other hand is going to struggle to calculate the flight path in before the ball gets to where it is going, let alone use the feedback from a vision system to make real time updates, in order to be able to predict the path to allow the interception by a hand sized object. This is extraordinarily difficult computationally, since it requires the simultaneous computation of multiple third order differential equations. Although not seeming so on a basic level the requirement here is of a similar level of difficulty for an AI system.

Although now getting on for 25 years ago I have had a little experience in this sort of thing. When I did my Electronics Engineering degree the lecturer who taught us C Programming for Engineers field of study was machine vision, specifically in cell biology, so most of our course work was writing image processing filters. I remember doing edge detection, and a couple of different interpolation algorithms, although nothing as advanced as Bicubic. But this was back in 92/93, and IIRC Photoshop was only on about version 1 or 2 maybe, and I don't think it had Bicubic yet then either. Fractals were the really new big thing then, and the talk was they might even be useful for using in interpolation. So i guess AI, which has been the next big thing for even longer in computing might actually solve this problem, if they ever get the AI systems actually working that is.

Alan


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Jan 16, 2017 09:23 |  #14

https://www.youtube.co​m/watch?v=hqB7rlmrSbo (external link)


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Picture ­ North ­ Carolina
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Jan 17, 2017 05:06 |  #15

Excellent. Thanks for the post. I have Raya Pro but don't use it often. Did not know it corrected CA and, in addition, that it either includes - or will include - frequency separation.

Jimmy McIntyre is an excellent instructor.


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Fixing chromatic abberation - best SW?
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