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05-31-2008, 06:26 AM   #1
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Magenta halo

I wonder how to prevent my shots from the magenta halo around high contrast objects. I attached two different exposures of the same object: one with long shutter and one with fast. Both are 100% crop with no modification - just converted from RAW to jpeg. I will continue working with the longer shutter version as I like it better but it would be nice to know for future images.




05-31-2008, 06:48 AM   #2
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QuoteOriginally posted by KungKrille Quote
I wonder how to prevent my shots from the magenta halo around high contrast objects. I attached two different exposures of the same object: one with long shutter and one with fast. Both are 100% crop with no modification - just converted from RAW to jpeg. I will continue working with the longer shutter version as I like it better but it would be nice to know for future images.
Stop shooting high contrast subjects.....

If you are using Photoshop, you can grab the purple fringe with the magic wand and alter the levels to bring the colour to something acceptable. I don't know the exact mechanics of doing it, but I suspect a web search for the technique should turn something up.

Last edited by Wheatfield; 05-31-2008 at 09:46 AM.
05-31-2008, 07:00 AM   #3
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I should have added that I also wonder why the effect appears on short shutter speeds and not on longer
05-31-2008, 07:05 AM   #4
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I use this technique:
Remove Purple Fringing From Your Photographs

By doing it fairly quick and dirty (and not adjusting contrast afterwards):


05-31-2008, 07:13 AM   #5
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Hi KungKrille

Re your question:

QuoteQuote:
I wonder how to prevent my shots from the magenta halo around high contrast objects.
That infuriating 'magenta halo' is commonly referred to as either CA (Chromatic Aberration) or Purple Fringing, an explanation of which I've included in the link below:

Chromatic aberration - Wikipedia, the free encyclopedia

Here is a brief summation:

QuoteQuote:
Chromatic Aberration is caused by a lens having a different refractive index for different wavelengths of light. Longitudinal and lateral Chromatic Aberration of a lens is seen as "fringes" of colour around the image, because each colour in the optical spectrum cannot be focused at a single common point on the optical axis.
Regrettably CA is present to a lesser or greater degree in the majority of photographic lenses, but it can thankfully be minimised to some extent by careful design & construction, employing the latest multi-coating techniques applied to individual elements of the lens. Purchasing & attaching a UV (Ultra Violet) filter to the front of your lens can help to reduce CA somewhat and thankfully it can be removed from your images at the editing stage using a computer in conjunction with many of today's inexpensive digital photo editing software programs such as Adobe Photoshop Elements v.6.0 or Paint Shop Pro X2 etc. In addition there are numerous entirely free editing programs out there on the internet for download via broadband internet connection which might be able to deal with CA removal. Try the URL below which contains direct links to some of the best examples:

https://www.pentaxforums.com/forums/256470-post11.html

Hope this info helps ?

Best regards
Richard

P.S. Incidentally, in another post by 'Wheatfield', interestingly he says:

QuoteQuote:
Pentax uses a less aggressive anti aliasing filter in the optical path making their cameras somewhat more prone to PF.

Last edited by Confused; 05-31-2008 at 09:35 AM.
05-31-2008, 08:30 AM   #6
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you can take it away in RAW post-processing quite easily.
thats what i do with my photos having that prob
05-31-2008, 09:15 AM   #7
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QuoteOriginally posted by jani Quote
you can take it away in RAW post-processing quite easily.
thats what i do with my photos having that prob
I didn´t find any parameters for that in my Photoshop Elements trial RAW extract version, but I will check inside the editor.

Thanks for all replies guys
05-31-2008, 09:21 AM   #8
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it is appearing on your shorter shutter durations not your longer ones, and that is because the offending high contrast areas are in motion during your longer exposures and therefore it is blurred together (no harsh edges)

05-31-2008, 10:27 AM   #9
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The pictures are as they should be!!!! White objects' shadows are blueish! Our brains know that they should be white/grey, so we see it as white/grey. But actually those shadows are blue. The impressionist painters (19th century, Monet, Manet, Van Gogh etc.) so painted the shadows blue. All colours have their own shadow-colours.
So I would say: your camera is doing fine!!
05-31-2008, 11:52 AM   #10
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QuoteOriginally posted by KungKrille Quote
I didn´t find any parameters for that in my Photoshop Elements trial RAW extract version, but I will check inside the editor.

Thanks for all replies guys
i am using that on photoshop cs3, so i cant tell how it would be on other versions
05-31-2008, 12:35 PM   #11
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Is the f-value the same in both pictures? Most lenses handle CA better stopped down a bit.
05-31-2008, 01:22 PM   #12
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Hi KungKrille

QuoteQuote:
The impressionist painters (19th century, Monet, Manet, Van Gogh etc.) so painted the shadows blue.
Sorry to spin off at a slight tangent for a moment, but an interesting fact emerged recently during a conversation that I was having with my optician, whilst I underwent an annual eye inspection. It seems the main reason why Van Gogh's colours are so vivid in his later paintings is that apparently Vincent suffered from cataracts as he grew older, a side-effect of which is to reduce the transmission of light, particularly in the blue wavelength ! So if digital cameras had been around at the time Van Gogh was painting, the likelihood is that he would never have been able to detect Chromatic Aberration......ain't life wonderful, you learn something useful every day..lol !

Best regards
Richard

Last edited by Confused; 05-31-2008 at 07:43 PM.
05-31-2008, 05:31 PM   #13
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QuoteOriginally posted by snigelben Quote
Is the f-value the same in both pictures? Most lenses handle CA better stopped down a bit.
Hehe, visste inte att sniglar har ben

No, the image with a slower shutter speed has a smaller aperature. After reading Confused´s link I think you are right about the relation between CA and aperature. You don´t see it in the first picture.
06-01-2008, 01:35 AM   #14
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QuoteOriginally posted by Confused Quote
Hi KungKrille



Sorry to spin off at a slight tangent for a moment, but an interesting fact emerged recently during a conversation that I was having with my optician, whilst I underwent an annual eye inspection. It seems the main reason why Van Gogh's colours are so vivid in his later paintings is that apparently Vincent suffered from cataracts as he grew older, a side-effect of which is to reduce the transmission of light, particularly in the blue wavelength ! So if digital cameras had been around at the time Van Gogh was painting, the likelihood is that he would never have been able to detect Chromatic Aberration......ain't life wonderful, you learn something useful every day..lol !

Best regards
Richard
lol only all people had that disease, we would never have to worry about CA
06-01-2008, 06:55 AM   #15
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Keep in mind that other manufacturers such as Olympus and Nikon (in the D300) have automatic CA and PF correction. The problem may exist in a picture but you don't see it as the camera corrects for it.
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