Help with defringing?

[webb]

I am trying to remove some purple and green fringing from an image using Affinity Photo 1.6.5 on Windows 10, but am having no luck.  I choose a live filter for defringing, and try to find a hue that matches (having slid the radius and tolerance to max and the threshold to min), but at best I get a subtle effect on the purple, and no effect on the green, no matter how many live filters I stack.

It would help if there were an eyedropper to select the color--as it is,  I have to count on the filter having a visible effect in the image to see whether it's the correct color. Maybe I haven't found the color, but there are limits to how slowly I can drag the slider (and wouldn't having tolerance at max mean that the range of colors affected is large?) So, since I can't see an effect, I wind up not knowing how close to the fringe color the slider actually is. For both purple and green, I tried a number of colors that looked about right (though they didn't have a visible effect), but with little or no success.

And "Also remove complementary color" seems to have no effect. 

It doesn't matter whether I try to do this in the Develop persona or the Photo persona - I get the same (lack of) effect.

The enclosed photo illustrates the problem. There is purple fringing in lots of places, including the right-hand side of the book, between the top cover and the cover jacket, and there is (out of focus, but more visible) green fringing on the left-hand side of the book, mostly on the top cover jacket itself.

I've tried various things like white balancing the photo (improves the color but the fringing remains) and using 'Select Sampled Color...' and then using it as a mask for an HSL adjustment layer to desaturate the color (some improvement, but some fringing still remains after a stack of 4 such adjustment layers.) 

Using the defringing eyedroppers in an old copy of Lightroom, I can successfully defringe--but of course I don't want to use Lightroom, I want to use Affinity Photo.

Am I doing something wrong?  Am I missing something? 

P.S. A stack of 4 live defringing filters seems to bring Affinity to a slow crawl on my machine (a 6-core Xeon E5-1650 v3 with 32 GB of memory and an SSD running Windows 10.) This doesn't seem to happen with the other live filters I've used.

[HVDB Photography]

Using Channel Mixer adjustment
Select CMYK >Magenta 
set the value to 60%

 

sample_fringe.afphoto

[Old Bruce]

I use the Lens > Defringe in the develop persona of Photo and get good results from raw files and non compressed files, I could do nothing to improve the little jpeg so I figure HVDB Photography's suggestion is the way to go.

 

[webb]

Thank you, @HVDB Photography, that definitely helps with this photo.

I'm concerned for other (and future) photos that also need defringing, as well. If there is no other (non-fringing) magenta in the photo, the Channel Mixer technique will work, but I thought that the defringing filter was supposed to look for the color in question near high-contrast edges and not affect other magenta in the photo that is not near high-contrast edges.  I guess I could use the Channel Mixer adjustment with suitable masking if there is "innocent" magenta in the photo, but I was hoping there was some trick to using the defringe filter that I am missing.

The reason this matters to me is that I have an old Nikon 50mm f/1.4 AI lens on a Metabones Speed Booster adapter for my Olympus E-M1 camera, and when wide open this lens creates an enormous amount of purple/magenta (and a little green) fringing where there is any degree of edge contrast. Obviously I'd like to be able to remove it conveniently. It may be that this lens and camera combination simply isn't workable for me wide open, but I was hoping there was a consistent and predictable way to remove fringing around edges.  The Affinity Photo defringe filter (live or non-live, in the Develop or the Photo persona) doesn't seem to work for this, at least not in the way I've been trying to use it.

@Old Bruce, I don't normally use Affinity Photo for raw development, but nevertheless I tried it with this photo, and Lens > Defringe didn't work any better for me in the Develop persona than in the Photo persona. I got the same (which is to say minimal) results.

So, my question is, is there something wrong with the way I'm using the defringe filter, or does it just not work for this kind of fringing?

[Old Bruce]

1 hour ago, webb said:

So, my question is, is there something wrong with the way I'm using the defringe filter, or does it just not work for this kind of fringing?

I would say  if you have narrowed it down to a particular lens used wide open then the program isn't going to be able to get you any better results. Too bad because that was a lovely piece of work.

[Gnobelix]

Hello @webb

take a look at this video.maybe that will help.

 

Cheers