Jump to content

Is this amount of colour fringing/ CA normal? or is there something wrong?


jaay
 Share

Recommended Posts

Advertisement (gone after registration)

When reviewing the vast majority of pictures that are shot in DNG on the lcd on my M8 i can see a lot of colour fringing/ CA around the highlights - is this just the way the M8 decodes the DNG for display on the lcd or is there a problem.

 

When i then put the images on my computer the majority of RAW converters leave a finished image with most (but not all) of this removed. C1, Aperture leave some. CS4 on the other hand removes it all. But should this be happening in the first place?

 

linked here are 2 DNGs shot today that show the issue a lot on my lcd:

the first shows it in the trees, a lot of blue fringing:

http://myweb.tiscali.co.uk/jaays/L1000390.DNG

the second shows blue fringing around the black railings:

http://myweb.tiscali.co.uk/jaays/L1000387.DNG

could someone who's been using the M8 for sometime take a look and put my mind at rest.

This is apparent on all my lenses btw.

 

thanks

Link to post
Share on other sites

I see no CA in you images at all. Uniformly blue fringes could be purple fringing, but you don’t see much of that in M8 images either, and definitely not in your examples. I suppose what you see are just demosaicing artifacts of the preview image.

Link to post
Share on other sites

Hi Jaay,

 

I have encountered this same issue myself on occasion. I find that Aperture seems to show it most, and Photoshop Elements the least. Do you shoot JPG and DNG together? If so, then you can put your mind at ease by looking at the JPG files. If they don't show the problem, then it's down to the RAW converter. I hope that Apple will come out with an improved RAW converter for M8 DNG files someday soon.

Link to post
Share on other sites

Thanks for the responses. And I'm glad that somone else has experienced this too and it's not either my sensor or me going mad! I agree that aperture needs to upgrade it's raw converter as it's just not up to dealing with the M8's DNGs. What's strange is despite owning serveral digital cameras before the M8 and always shooting raw i've never seen it before.

Link to post
Share on other sites

I see a few small colour artefacts in the leaves of the trees using ACR, when I opened in C1 4.8.1 all had disappeared and the image was clean.

The second image was flawless in both ACR and C1.

Edited by jaapv
Link to post
Share on other sites

So the answer is simply in the raw converter?

 

Yes. Nicole recently had a thread with a similar problem. Same answer. :)

I would strongly recommend the newest version of C.4.8.1. which has even better defenses against this kind of thing, especially purple fringing on high contrast edges.

 

See this thread as well:

http://www.l-camera-forum.com/leica-forum/leica-m8-forum/86126-21-1-4-needs-c1-4-a.html

Link to post
Share on other sites

Yes. Nicole recently had a thread with a similar problem. Same answer. :)

I would strongly recommend the newest version of C.4.8.1. which has even better defenses against this kind of thing, especially purple fringing on high contrast edges.

 

See this thread as well:

http://www.l-camera-forum.com/leica-forum/leica-m8-forum/86126-21-1-4-needs-c1-4-a.html

 

Which raw converter you use won't solve this annoyance. It happens on all Leica 1.4 and faster lenses shot wide open. Even on the new 21mm 1.4 in open shade you'll see wide blue edges surrounding black / white contrast areas. Erwin Puts recently wrote about this occurrence when he reviewed the new 095 Noctilux.

 

"...we see also the occurrence of the blue fringes at the edges of black/white transitions. This phenomenon is a chromatic aberration and is almost impossible to avoid in high speed lenses. The correction of the blue part of the spectrum for this type of lenses cannot be accomplished by simply selecting exotic glass types from the glass catalogues: it is a balancing act between all aberrations, focal length, back focus and so on. The previous Noctilux lenses also showed a significant amount of blue fringing. But is was less visible. Many pictures were made on black and white film, color film was less responsive in the blue region, most pictures were taken in artificial light where red is over-represented."

 

When using a M8 at 1.4 (or wider) you have to be VERY careful of what your shooting or be ready to spend some time in Photoshop correcting those blue/purple areas.

Link to post
Share on other sites

I only opened image one, in C1 as I am most familiar with that, and was more concerned with the geometric distortion than than any chromatic effects. The limited processing power available in camera will not correct the lcd view fully it is only a preview for exposure, focus and composition not for final display. If there was a trace of blue fringing I struggled to find it at 100% but I did find a little sensor dust :). If you are unhappy with the blue edge you see in that shot you are going to struggle to find happiness with this set up that is as good as it gets here and you are looking at MFDB on an Alpa with schneider apo-digitars or Rodenstock HR Digaron-S Digital lenses but you might find that is not as portable.:)

Link to post
Share on other sites

Thanks for the further responses. I'm using the latest C1 now and it makes a noticable quality difference in the image and I can use the colour noise reduction to remove the issues I was seeing.

 

It was not wide open shooting as it was f8 on the voigtlander 15mm lens - hence the distortion!

 

It does somewhat render aperture useless as although it allows the non destructive imaging with the original raw, the conversion is insufficient to make it worth using. The 100% crop differences on tiff files from latest C1, aperture and CS4 are quite dramatic.

Link to post
Share on other sites

Which raw converter you use won't solve this annoyance. It happens on all Leica 1.4 and faster lenses shot wide open. Even on the new 21mm 1.4 in open shade you'll see wide blue edges surrounding black / white contrast areas. Erwin Puts recently wrote about this occurrence when he reviewed the new 095 Noctilux.

 

"...we see also the occurrence of the blue fringes at the edges of black/white transitions. This phenomenon is a chromatic aberration and is almost impossible to avoid in high speed lenses. The correction of the blue part of the spectrum for this type of lenses cannot be accomplished by simply selecting exotic glass types from the glass catalogues: it is a balancing act between all aberrations, focal length, back focus and so on. The previous Noctilux lenses also showed a significant amount of blue fringing. But is was less visible. Many pictures were made on black and white film, color film was less responsive in the blue region, most pictures were taken in artificial light where red is over-represented."

 

 

 

When using a M8 at 1.4 (or wider) you have to be VERY careful of what your shooting or be ready to spend some time in Photoshop correcting those blue/purple areas.

Have a look on the thread I posted - it shows a dramatic reduction by C1 -newest version - on a Summilux 24 wide open. Try C1. ACR and Aperture are simply not up to standard for these highly critical lenses

Link to post
Share on other sites

When reviewing the vast majority of pictures that are shot in DNG on the lcd on my M8 i can see a lot of colour fringing/ CA around the highlights - is this just the way the M8 decodes the DNG for display on the lcd or is there a problem.

 

I have seen many posts about colour fringing, CA etc, but I have never seen anybody clearing out this mess, and people seem very confused and often get it wrong. I'm not the ultimate expert on the subject, but I have done some digging and this is what I found. Perhaps someone knowledgeable like mjh could correct and confirm what I say here.

 

There are actually (at least) three factors to deal with:

 

1. demosaicing of the image for the LCD

2. CA in the lens

3. flare across sensor microlenses

 

I will say a few words about each, but to get to my point, I believe 9 out of ten times we are dealing with (3).

 

On (1), and this is based on my own observation, I think Leia changed the demosaicing algorithms between firmware 1.110 and 1.201 because since then I have seen this in many images on my LCD. Overall the IQ on the LCD is better, but there is often colour artifacts along contrasty borders. E.g. take a photograph of a white flag pole in bright sunlight. Notice that the artifacts change and even disappear as you zoom in. You will typically not see this in your raw converter on your computer. I agree with mjh that this is probably what the OP is seeing.

 

On (2), most modern Leica lenses are very well corrected. Some are even marked "APO" but e.g. the 50 Lux ASPH is APO even though it is not marked as such (see dfarkas blog interview with Peter Karbe). I'm sure even Leica struggle with CA in lenses like the new Noct f0.95 wide open, but even so, I suggest that in most cases the "CA or whatever they call it" that people see is not the classical CA created by the lens.

 

With (3) I think we have, ignoring the LCD problem in (1), the source of almost all the problems that people observe. According to "photographic expert" Geoffrey Crawley, fringing or blooming may be seen on subjects outlined against a bright background such as the sky. This is the result of flare across the sensor microlenses rather than camera lens aberration. The steep angles from large apertures will hardly make it better. I believe he has confirmed this with Leica themselves. I have several photographs were this is apparent, and yet when I use the same lens under other conditions the image is virtually perfect all the way to the outer corners, even at wide open aperture.

 

So, in practice, ignore colour artifacts on the LCD, avoid subjects against a bright background if you can, and as jaapv says use the latest version of C1 for your DNG's.

 

Regards

Per

Link to post
Share on other sites

With (3) I think we have, ignoring the LCD problem in (1), the source of almost all the problems that people observe. According to "photographic expert" Geoffrey Crawley, fringing or blooming may be seen on subjects outlined against a bright background such as the sky. This is the result of flare across the sensor microlenses rather than camera lens aberration. The steep angles from large apertures will hardly make it better. I believe he has confirmed this with Leica themselves. I have several photographs were this is apparent, and yet when I use the same lens under other conditions the image is virtually perfect all the way to the outer corners, even at wide open aperture.

This purple fringing is a rather strange phenomenon with some unusual characteristics; it has been baffling the experts for years. There have been various explanations proposed that turned out to be wrong; arguably the craziest explanation so far has been the suggestion that purple fringing was caused by birefringence in the microlenses. Longitudinal chromatic aberration was another, more popular explanation. Now I have been wrong on this before (for some time I thought the longitudinal CA theory had some plausibility), but I am fairly sure by now that purple fringing is, much like you said, caused by flare within the sensor assembly, occurring at some point behind the RGB filters. After passing the color filters, stray light contaminating adjacent sensor pixels will appear as blue/violet in the eventual image. The red and blue filters have a lower transmission than the green filters, so the raw image data has a greenish tint that needs to be removed in image processing by amplifying red and especially blue. Any stray light spreading to neighboring pixels after having passed the RGB filters will affect all kinds of sensor pixels evenly, so when red, green, and blue sensitive pixels receive the same additional amount of light due to flare, blue and red will eventually dominate because of the extra boost these color channels receive during image processing. (This is also the reason why the smearing artifacts that plague the displays of compact cameras are usually blue or violet rather than white, even when smearing affects red, green, and blue sensitive pixels evenly.)

 

But however this may be, the biggest issue with the M8 was its substandard demosaicing algorithm that used to create artifacts along high contrast edges in JPEG and preview images. As you said, this has improved considerably in recent versions of the firmware.

Link to post
Share on other sites

I had some extreme examples in some shots and I asked for the reason in this German thread:http://www.l-camera-forum.com/leica-forum/forum-zur-leica-m8/88064-ca-luftspiegelung-schl-mpfe.html (m8.2 with Summicron 75 asph and bw-filter @ 1/1000 s shot from the dark shadow outside in a blazing noon scene. No windows there)

 

There is no difference in processing in Aperture or C1. The crop from jaay first shot shows exacly the same (but much weaker) blue areas.

 

Well, I do not understand the technical details of Per and Michael. But it sound at least possible to me. Maybe the absolute regularity of the ghost image gives some hints for verification.

 

(pic 1: crop form jaays first example, pic 2 crop from me)

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

Edited by Fokalfissur
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
×
  • Create New...