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Double CA correction?
  
 
Fred Miranda
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p.1 #1 · p.1 #1 · Double CA correction?


When checking some of my older images for Lateral CA correction, I noticed that the Lightroom's correction (Remove Chromatic aberration checkbox) does not take into account whether or not the image was already CA compensated in-camera.

So, If you have your camera's "Chro. Aber. Comp." set to Auto, you MUST unchecked the Lightroom's "Remove Chromatic aberration" checkbox or your image won't be corrected properly.

In short: It looks like we need to set CA correction in-camera OR in Lightroom. (or perhaps Capture One)

I may run some tests and see which one does a better job but perhaps someone already tried this.

Let me know your thoughts.
Fred



Sep 14, 2017 at 03:44 AM
bluloo
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p.1 #2 · p.1 #2 · Double CA correction?


I think I've had mine set to "auto", for some time now.

Never much thought about that, but now I wonder how detrimental the double correction has been...



Sep 14, 2017 at 03:56 AM
Fred Miranda
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p.1 #3 · p.1 #3 · Double CA correction?


bluloo wrote:
I think I've had mine set to "auto", for some time now.

Never much thought about that, but now I wonder how detrimental the double correction has been...


Same here. The only in-camera correction I always had was CA set to "Auto".

We need to run some controlled tests to make sure but the images I've checked for CA so far (from my CV 15/4.5III and 35/1.4ZA lenses) look much better with Lightroom's CA correction "unchecked" and I was also surprised by this.



Sep 14, 2017 at 04:01 AM
DavidBM
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p.1 #4 · p.1 #4 · Double CA correction?


Fred Miranda wrote:
When checking some of my older images for Lateral CA correction, I noticed that the Lightroom's correction (Remove Chromatic aberration checkbox) does not take into account whether or not the image was already CA compensated in-camera.

So, If you have your camera's "Chro. Aber. Comp." set to Auto, you MUST unchecked the Lightroom's "Remove Chromatic aberration" checkbox or your image won't be corrected properly.

In short: It looks like we need to set CA correction in-camera OR in Lightroom. (or perhaps Capture One)

I may run some tests and see which one does a better job but perhaps someone already tried this.
...Show more

Fred I thought that for RAW files in Lightroom, it makes no difference what you set the in camera CA correction to: the auto profile which Lightroom applies corrects CA (though oddly it does make a difference with vignetting) and you get the attached message when you click on the info button for the automatic profile:

Chromatic abberation correction is set to OFF on my body, and this affects JPEGS, but the RAW files, at least in LR get compensated. So best maybe to turn the checkbox off which may cause a second attempt?

Maybe whether this is true depends on whether its a lens which has an auto profile registered: which means a native lens that does EXIF etc. These auto profiles are created by the lens maker, and aren't the same thing as LRs profiles which can be applied automatically (as I'm sure you know, but perhaps not everyone)








Sep 14, 2017 at 04:31 AM
Fred Miranda
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p.1 #5 · p.1 #5 · Double CA correction?


DavidBM wrote:
Chromatic abberation correction is set to OFF on my body, and this affects JPEGS, but the RAW files, at least in LR get compensated. So best maybe to turn the checkbox off which may cause a second attempt?


When I check images shot using in-camera CA set to "Auto", disabling Lightroom's CA correction makes CA actually improve.
Not very intuitive, but that's what I see in many of my images. (native lenses)

As you wrote, setting in-camera to "Off" does not seem to affect how LR sees the RAW files either
Perhaps, with native lenses, it's best to leave LR's CA corrected unchecked. (regardless of the camera setting)...That's something I need to test further.



Sep 14, 2017 at 04:55 AM
DavidBM
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p.1 #6 · p.1 #6 · Double CA correction?


Fred Miranda wrote:
When I check images shot using in-camera CA set to "Auto", disabling Lightroom's CA correction makes CA actually improve.
Not very intuitive, but that's what I see in many of my images. (native lenses)

As you wrote, setting in-camera to "Off" does not seem to affect how LR sees the RAW files either
Perhaps, with native lenses, it's best to leave LR's CA corrected unchecked. (regardless of the camera setting)...That's something I need to test further.


Yep Fred that might be right.

I have often left the checkbox in LR left on, just because it's easy to do as part of input profiling, and it helps most lenses, and I assumed it would be able to tell if the auto-profile had been applied, or maybe even fix some residual issues.

But if you are seeing worse results on native lenses with the LR checkbox turned on, since we can't in LR (or C1) disable the auto profile for CA, I guess we need a different input profile for native and non-native lenses. I'll see if I can replicate the worse results. I'd be interesting if you could show us the 1.4/35 ZA image with CA in the corners you showed us, with checkbox on and off....




Sep 14, 2017 at 05:14 AM
Gunzorro
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p.1 #7 · p.1 #7 · Double CA correction?


Where is the CA correction shown on the menu for a7R and a7R2?

I've probably drifted past it on my two passes on each body!

************
Just went through it two more times on each body -- don't see it in menu. I must be operating on post-hypnotic suggestion!

Edited on Sep 14, 2017 at 05:35 AM · View previous versions



Sep 14, 2017 at 05:20 AM
DavidBM
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p.1 #8 · p.1 #8 · Double CA correction?


Hmm

I'm getting in some respects better results with the checkbox ON with 1.4/35

See these crops (at 2:1)

BUT
In places I'm seeing elsewhere some odd colour effects bleeding past borders with the checkbox on. Which makes no sense for standard LaCA correction where you adjust the magnification of the colour channels. It's a tell-tale sign of some sort of attempt to do something about LoCA......





Checkbox OFF







Checkbox ON




Sep 14, 2017 at 05:25 AM
DavidBM
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p.1 #9 · p.1 #9 · Double CA correction?


I have a ghastly feeling it may be a case-by-case thing whether the checkbox is better. Which is a nuisance, to say the least.


Sep 14, 2017 at 05:27 AM
Fred Miranda
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p.1 #10 · p.1 #10 · Double CA correction?


DavidBM wrote:
Hmm

I'm getting in some respects better results with the checkbox ON with 1.4/35

See these crops (at 2:1)

BUT
In places I'm seeing elsewhere some odd colour effects bleeding past borders with the checkbox on. Which makes no sense for standard LaCA correction where you adjust the magnification of the colour channels. It's a tell-tale sign of some sort of attempt to do something about LoCA......


Is this crop from the corners of the image?



Sep 14, 2017 at 05:35 AM
 

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DavidBM
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p.1 #11 · p.1 #11 · Double CA correction?


Fred Miranda wrote:
Is this crop from the corners of the image?


No, top centre edge, which makes me think the colour might be axial, and thus the check box correction more complicated than we thought...



Sep 14, 2017 at 06:38 AM
timballic
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p.1 #12 · p.1 #12 · Double CA correction?


I did report on this a few weeks back on my thread: http://www.fredmiranda.com/forum/topic/1503029/1
Though there I majored on the corner shading aspect being doubled up pg2 #7. "I am amazed to find that Lr6.12 does indeed double up the corrections!!!"

Surprised me that no one followed up on it.



Sep 14, 2017 at 12:15 PM
bluloo
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p.1 #13 · p.1 #13 · Double CA correction?


Gunzorro wrote:
Where is the CA correction shown on the menu for a7R and a7R2?

I've probably drifted past it on my two passes on each body!

************
Just went through it two more times on each body -- don't see it in menu. I must be operating on post-hypnotic suggestion!


Gear -> #7 -> Lens Comp



Sep 14, 2017 at 02:57 PM
Fred Miranda
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p.1 #14 · p.1 #14 · Double CA correction?


DavidBM wrote:
Yep Fred that might be right.

I have often left the checkbox in LR left on, just because it's easy to do as part of input profiling, and it helps most lenses, and I assumed it would be able to tell if the auto-profile had been applied, or maybe even fix some residual issues.

But if you are seeing worse results on native lenses with the LR checkbox turned on, since we can't in LR (or C1) disable the auto profile for CA, I guess we need a different input profile for native and non-native lenses. I'll see if I can replicate
...Show more


Here is are some edge crops (2:1) from a CV 15/4.5III FE mount. (Camera was set to CA correction: Auto)
The LR's Correct CA 'unchecked' box has better correction as I mentioned earlier. Same so my images from 35/1.4 ZA and others.






Lightroom's Remove Chromatic Aberration







Lightroom's Remove Chromatic Aberration




Sep 15, 2017 at 12:18 AM
Fred Miranda
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p.1 #15 · p.1 #15 · Double CA correction?


So, I don't think it makes a difference if the in-camera setting is "auto" or "off" and I believe we should leave LR's CA correction 'unchecked' when dealing with native lenses.


Sep 15, 2017 at 12:20 AM
DavidBM
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p.1 #16 · p.1 #16 · Double CA correction?


Fred Miranda wrote:
So, I don't think it makes a difference if the in-camera setting is "auto" or "off" and I believe we should leave LR's CA correction 'unchecked' when dealing with native lenses.


This is puzzling.
The crop I posted above is far from unusual.
In which case it's not at all clear what we will get best results from.
Agreed yours are slightly better with unchecked, but the ones I'm seeing are slightly better checked.

Here is a possibility.
The checkbox does two things: does a LaCA correction by resizing channels, but also tries to correct LoCA with auto defringening.

The second LaCA correction makes things worse, while the LoCA correction makes things better (at the cost of some artefacts)

Maybe we could be better off leaving the check box off, and doing our defringeing manually to minimise artefacts.

But if this is true there's another problem: with NON native lenses, we have no way to correct only the LaCA (which is lossless) without having an auto attempt at LoCA.



Sep 15, 2017 at 12:42 AM
DavidBM
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p.1 #17 · p.1 #17 · Double CA correction?


Here are a couple of 2:1 crops from a slightly OOF top right midfield area.

As you can see the checkbox significantly reduces the green-cyan fringe; but it also does some weird stuff like spread a green-cyan blob of colour into the bushed above some of the fence...

This is not the behaviour of LaCa correction: something else is going on.
However, on balance, correction ON is better (maybe manual defringing could do better)





LR Correction OFF







LR Correction ON




Sep 15, 2017 at 12:48 AM
DavidBM
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p.1 #18 · p.1 #18 · Double CA correction?


Indeed manual defringeing can do better.

So this confirms a problem for non native lenses: no way to engage the LaCa correction without suboptimal auto attempts at other defringeing.





Check box off, fringing colour set by dropper, amount by eye.




Sep 15, 2017 at 12:53 AM
Fred Miranda
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p.1 #19 · p.1 #19 · Double CA correction?


DavidBM wrote:
This is puzzling.
The crop I posted above is far from unusual.
In which case it's not at all clear what we will get best results from.
Agreed yours are slightly better with unchecked, but the ones I'm seeing are slightly better checked.

Here is a possibility.
The checkbox does two things: does a LaCA correction by resizing channels, but also tries to correct LoCA with auto defringening.

The second LaCA correction makes things worse, while the LoCA correction makes things better (at the cost of some artefacts)

Maybe we could be better off leaving the check box off, and doing our defringeing manually to minimise artefacts.

But
...Show more

I always thought that LR's "reduce chromatic aberration" was only targeting 'lateral' CA and not 'axial'. From you sample (since it's not towards the edge), it does seem it's targeting both automatically. If it is, it's doing a very poor job reducing axial CA while making Lateral CA actually worse (since the RAW images seem to be already corrected in camera)

I still don't know for sure what's happening but my images have lower "lateral" CA with the checkbox 'unchecked'. (native lenses)



Sep 15, 2017 at 03:48 AM
DavidBM
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p.1 #20 · p.1 #20 · Double CA correction?


Fred Miranda wrote:
I always thought that LR's "reduce chromatic aberration" was only targeting 'lateral' CA and not 'axial'. From you sample (since it's not towards the edge), it does seem it's targeting both automatically. If it is, it's doing a very poor job reducing axial CA while making Lateral CA actually worse (since the RAW images seem to be already corrected in camera)

I still don't know for sure what's happening but my images have lower "lateral" CA with the checkbox 'unchecked'. (native lenses)


Yep that's my take.

Which is fairly OK with native lenses; we can turn the checkbox off, and get the better lateral CA correction with the built in profile. Then we can use the dropper and sliders to do our own axial CA correction.

But we have a dilemma with non-native lenses. If we use the checkbox to reduce lateral CA, as often we will, it seems we have to put up with the dodgy auto axial CA correction.

I suppose I should check whether it looks like axial CA is being targeted with non-native lenses, but it's hard to see why it would be different..



Sep 15, 2017 at 04:02 AM
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