Purple fringe--what to do about it and why [1/5] - "101 Jim-LeroyWVA-001.jpg" yEnc (0/1)

Some people think they see auras around other people. But digital cameras often think they see purple fringes around the edges of some objects, and it makes pictures look less sharp. To illustrate what can be done about the problem, I've used a picture that was uploaded by Andrew.

Image 101 shows the unmodified image. Image 102 is a magnified portion of the bottom of the fuselage, clearly showing the purple edge (blow up 101, and you'll also see it on the upper wing and the bottom of the wheel). Image 103 shows the problem corrected. How was it done? Paint Shop Pro's one-step purple fringe was ineffective in this case. Instead, I used PSP's Chromatic Aberration Removal tool. With it, you create samples (basically, rectangles containing problem areas so that PSP knows what colors it should treat as aberrations--I'm oversimplifying), and then simply let PSP take care of all instances of the problem. Image 104 shows the whole airplane corrected, done in just one step. Compare it with 101, and it simply looks sharper even though it really isn't!

Unrelated to the purple fringe problem, I was bothered by the fact that the upper wing seemed to be paler than the lower wing or tailplane. I was sure this was an artifact of lighting rather than any real color difference, so I darkened the upper wing a bit and kicked the saturation quite a bit to get much closer to a match, as seen in Image 105.

I prefer Image 105 to 101. How about you?

ck (Just Plane Noise) wrote in
:



I prefer Image 105 to 101. How about you?

Looks to me that the purple fringe was replaced by a yellow one, equally
unsharp.

Perhaps the answer lies in a better lens?
As far as I know, chromatic abberation is caused by the lens, not the
camera, so the best policy is to tackle the problem where it occurs.

But I'm not a professional photographer, so this is just my two cents...

And yes, the yellow in the top wing looks much better in pic 105, but
unfortunately the publicity on that wing now suffers from artefacts.

Not that I could have done any better, but since you asked for an
opinion... ;-)


Cave putoriem,

Steven

"Steven" wrote in message
.. .
ck (Just Plane Noise) wrote in
:



I prefer Image 105 to 101. How about you?

Looks to me that the purple fringe was replaced by a yellow one, equally
unsharp.

Perhaps the answer lies in a better lens?
As far as I know, chromatic abberation is caused by the lens, not the
camera, so the best policy is to tackle the problem where it occurs.

Yes true but the Fuji S1 (my first digital camera) had purple hallows under
low light conditions. It was a known issue with Fuji,
You just had to deal with it.

But I'm not a professional photographer, so this is just my two cents...

And yes, the yellow in the top wing looks much better in pic 105, but
unfortunately the publicity on that wing now suffers from artefacts.

Not that I could have done any better, but since you asked for an
opinion... ;-)


Cave putoriem,

Steven

On Thu, 09 Aug 2007 07:00:08 GMT, Steven wrote:

(Just Plane Noise) wrote in
m:



I prefer Image 105 to 101. How about you?

Looks to me that the purple fringe was replaced by a yellow one, equally
unsharp.


Ah, you're absolutely correct. That's what I get for being lazy and
trying to do the plane in one fell swoop (that's what also caused the
artifacts you mentioned below). So I went back and corrected the
fringe piece by piece using the freehand selection tool. I think
you'll find it looks a lot better.

Perhaps the answer lies in a better lens?

As far as I know, chromatic abberation is caused by the lens, not the
camera, so the best policy is to tackle the problem where it occurs.

That digital photo site whose URL I've been posting gives a very
technical explanation, saying it actually has something to do with
microlenses, which are part of the camera, not the lenses you attach.

But I'm not a professional photographer, so this is just my two cents...

And yes, the yellow in the top wing looks much better in pic 105, but
unfortunately the publicity on that wing now suffers from artefacts.

Not that I could have done any better, but since you asked for an
opinion... ;-)

Seriously, thanks. I was embarrassed after reading your comments,
which impelled me to do better. More could be done to this picture,
but ultimately you're dealing with an image that started out less than
completely sharp, perhaps because the image was too much of a blowup,
the camera's resolution wasn't that great, the plane was just moving
too fast, or some combo of these and other factors. Still, it's a
cool pic, and if you don't try to print it too big, it is quite
satisfactory.

(This is the pilot that died recently, right? If so, I hope I did him
a tiny bit of honor by making his plane look better.)

Forgot to attach this--sorry, Steven!

Sometimes the fringe is not caused by the lens but the imaging chip, be it
CCD or CMOS.

All chips have a "lens" built into them for light gathering. It is micro
etched onto a layer just above the sensor. The problem comes from when the
light path into the sensor is not perpendicular to the lens on the sensor.
As these are essentially simple meniscus lenses, chromatic aberration
happens. It is very noticeable with wide angle lenses, This is why several
manufactures have created "digital" lenses to move the rear element of the
camera lens further away from the sensor, which minimizes the effect.



"Steven" wrote in message
.. .
ck (Just Plane Noise) wrote in
:



I prefer Image 105 to 101. How about you?

Looks to me that the purple fringe was replaced by a yellow one, equally
unsharp.

Perhaps the answer lies in a better lens?
As far as I know, chromatic abberation is caused by the lens, not the
camera, so the best policy is to tackle the problem where it occurs.

But I'm not a professional photographer, so this is just my two cents...

And yes, the yellow in the top wing looks much better in pic 105, but
unfortunately the publicity on that wing now suffers from artefacts.

Not that I could have done any better, but since you asked for an
opinion... ;-)


Cave putoriem,

Steven

Just Plane Noise wrote in
:


begin 644 107 Jim-LeroyWVA-001.jpg

Attachment decoded: 107 Jim-LeroyWVA-001.jpg
`
end


Excellent work!


Cheers,

Steven