I just know that I get purple or green or red fringing with the Canon
lenses that I never get with any Leica lens. It drives me crazy! I will
try your suggestions.
Thank you,
Tina
On Sat, Feb 22, 2014 at 4:38 PM, Chuck Norcutt <
chucknorcutt@xxxxxxxxxxxxxxxx> wrote:
> I don't think it's chromatic aberration. The "purple defringing" slider
> under lens corrections in ACR significantly reduces the saturation of
> the purple fringe there but does not eliminate it.
>
> There are two types of chromatic aberration, axial and transverse and
> this image doesn't seem to fit either. Axial CA appears throughout the
> image while transverse CA doesn't show in the center but gets gradually
> worse the greater the angle off-axis. The only place we see "chroma" in
> this image is a small area nearly in the center. Therefore this is not
> chroma but "purple fringing". The following is from the Wiki article on
> chromatic aberration, the photography section that discusses purple
> fringing:
> <http://en.wikipedia.org/wiki/Chromatic_aberration#Photography>
> -----------------------------------------------------------------------
>
> The term "purple fringing" is commonly used in photography, although not
> all purple fringing can be attributed to chromatic aberration. Similar
> colored fringing around highlights may also be caused by lens flare.
> Colored fringing around highlights or dark regions may be due to the
> receptors for different colors having differing dynamic range or
> sensitivity – therefore preserving detail in one or two color channels,
> while "blowing out" or failing to register, in the other channel or
> channels. On digital cameras, the particular demosaicing algorithm is
> likely to affect the apparent degree of this problem. Another cause of
> this fringing is chromatic aberration in the very small microlenses used
> to collect more light for each CCD pixel; since these lenses are tuned
> to correctly focus green light, the incorrect focusing of red and blue
> results in purple fringing around highlights. This is a uniform problem
> across the frame, and is more of a problem in CCDs with a very small
> pixel pitch such as those used in compact cameras. Some cameras, such as
> the Panasonic Lumix series and newer Nikon and Sony DSLRs, feature a
> processing step specifically designed to remove it.
>
> On photographs taken using a digital camera, very small highlights may
> frequently appear to have chromatic aberration where in fact the effect
> is because the highlight image is too small to stimulate all three color
> pixels, and so is recorded with an incorrect color. This may not occur
> with all types of digital camera sensor. Again, the de-mosaicing
> algorithm may affect the apparent degree of the problem.
> ------------------------------------------------------------------------
>
> Note especially the discussion about about purple fringing around
> highlights and especially about blown highlights. The area of fringing
> follows much, but not all, of the contour of his light colored cap which
> is also in bright sun. This area does not now measure as blown but may
> have been before you started processing or perhaps was only blown in the
> green channel. Also, looking at his right hand there is a great deal of
> motion blur. I suspect that he also moved his head slightly and the
> purple fringe area is somehow mixed up with motion blur and blown
> highlights. In any case I don't think this is any fault of your lens.
> Fixing this is going to take some PS work. I think I'd try a selection
> on the fairly uniform purple color followed by desaturation or color
> change to match the cap or any of several other possible methods to
> cover it up or eliminate it.
>
> Chuck Norcutt
>
>
>
> On 2/22/2014 1:39 PM, Tina Manley wrote:
> > The Remove Chromatic Aberration button in LR did not work on this one:
> >
> > http://www.pbase.com/tinamanley/image/154578993
> >
> > It has done a remarkable job on most of the awful CA from the Canon
> wides,
> > but it barely touched the purple fringe on his cap. UGH!
> >
> > Tina
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>
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Tina Manley
http:// <http://tina-manley.artistwebsites.com/>www.tinamanley.com
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