Digital BW, The Print

Some of the best 6 and 8 MP digicams suffer significant purple fringe
at high ei. What's the impact on B&W conversions? Obnoxious? Vanished?

Hello Djon,
 
>Some of the best 6 and 8 MP digicams suffer significant purple fringe
>at high ei. What's the impact on B&W conversions? Obnoxious?
Vanished?

I use a Canon Pro-1 8mp, which has only a small amount of PF in
extreme contrast areas like branches over skies.  A recent photo that
had a small amount showed none in the BW version.  I wasn't thinking
about it at the time, so I didn't do anything special for it.  I don't
know if it generally does not transfer to BW, or if my conversion
technique happens to reduce it.  It's not an issue with this camera,
but next time I find some I'll try some different techniques & see
what happens.  


Regards,
Clayton


Info on black and white digital printing at    
http://www.cjcom.net/digiprnarts.htm

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Djon"
<westsidemaurice@y...> wrote:
> 
> Some of the best 6 and 8 MP digicams suffer significant purple
fringe
> at high ei. What's the impact on B&W conversions? Obnoxious?
Vanished?

Funny you should ask. I recently worked on a RAW image of a winter
(snow) scene taken with my 5 mp Canon S50. After converting from RAW
and then doing a B&W conversion, I began to notice some strange
lines-- "ghosts"-- in the image: these pale lines ran alongside
(parallel to) various high-contrast edges throughout the image
(wherever there was snow against dark background. 

I suspected that this was an artifact from the initial RAW conversion,
so I repeated the RAW conversion (with slight changes) and then
started to redo the RGB-to-monochrome conversion. I was using Channel
Mixer for obtaining the grayscale, and I realized that I had been
using a relatively large percentage of the blue channel. That's when I
had a "duh! moment" and started backing off on the blue level. I could
clearly see those "ghost" fringes begin to disappear. A close look at
the RGB image showed that there indeed was a small amount of chromatic
abberations (purple fringing) along those same edges. But in color, it
actually seemed less noticeable than the corresponding pale "ghosts"
in the B&W version.

So--go easy on the blue channel (which is common practice anyway
because of noise issues).

Phil

Phil

Keep in mind that lenses don't focus all colors on the same plane.  It was
great for color film since the film also has separate layers.

True the digital glass is tweaked for digital, but a point and shoot doesn't
get all the technology and quality of high-end glass.   It's all about
price, features and megapixels.

"Yuz pays ur money and yuz takes ur chances"

Seth

==-----Original Message-----
==From: Phil Rose [mailto:pjrose@...] 
==
==Funny you should ask. I recently worked on a RAW image of a winter
==(snow) scene taken with my 5 mp Canon S50. After converting 
==from RAW and then doing a B&W conversion, I began to notice 
==some strange
==lines-- "ghosts"-- in the image: these pale lines ran 
==alongside (parallel to) various high-contrast edges 
==throughout the image (wherever there was snow against dark 
==background. 
==

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Seth"
<seth@m...> wrote:
>  Keep in mind that lenses don't focus all colors on the same plane.

Isn't that exactly what the term "chromatic abberations" (as used in
my post) means?

  It was
> great for color film since the film also has separate layers.
> 
> True the digital glass is tweaked for digital, but a point and shoot
doesn't
> get all the technology and quality of high-end glass.   It's all about
> price, features and megapixels.
> 
> "Yuz pays ur money and yuz takes ur chances"
> 

So what's your point--except the obvious? My point was simply to try
to answer the previous question by describing my experience--that
chromatic abberations can appear much more severe in a converted B&W
than in the original color image; and that judicious use of the
blue-channel info can minimize the problem in B&W. Naturally by using
better optics that avoid chromatic abberations you can, well, avoid
chromatic abberations/purple fringing.

Phil.

> 
> ==-----Original Message-----
> ==From: Phil Rose [mailto:pjrose@f...] 
> ==
> ==Funny you should ask. I recently worked on a RAW image of a winter
> ==(snow) scene taken with my 5 mp Canon S50. After converting 
> ==from RAW and then doing a B&W conversion, I began to notice 
> ==some strange
> ==lines-- "ghosts"-- in the image: these pale lines ran 
> ==alongside (parallel to) various high-contrast edges 
> ==throughout the image (wherever there was snow against dark 
> ==background. 
> ==

Yes. My only digicam is a two-yr-old antique Canon 3.2 ...it seems not
to produce purple fringes... I've been thinking about the Olympus
c8080 which reportedly equals Olympus DSLR optics...

Rodinal, an ancient B&W film developer, puts a black line at that
border, where you have white...one of the reasons it's survived so
long (it's also ultra-sharp, doesn't dissolve grain). 

What I'm wondering is actually "which digicam most closely
approximates an old Leica in B&W?"  In other words, discrete /
fast-responding / optically excellent. 

However a white fringe would look too much like oversharpening. Black
fringe might however be attractive, like darkroom diffusion or Rodinal. 


 I began to notice some strange

> lines-- "ghosts"-- in the image: these pale lines ran alongside
> (parallel to) various high-contrast edges throughout the image
> (wherever there was snow against dark background. 
>

I wasn't picking on you. I was explaining to those who didn't understand WHY
it's there and WHY those cameras do that.

Chill!!

Seth 

==-----Original Message-----
==From: Phil Rose [mailto:pjrose@...] 

==> 
==
==So what's your point--except the obvious? My point was simply 
==to try to answer the previous question by describing my 
==experience--that chromatic abberations can appear much more 
==severe in a converted B&W than in the original color image; 
==and that judicious use of the blue-channel info can minimize 
==the problem in B&W. Naturally by using better optics that 
==avoid chromatic abberations you can, well, avoid chromatic 
==abberations/purple fringing.
==
==Phil.
==

An Epson RD-1 with a Summilux.

Guy
--- Djon <westsidemaurice@...> wrote:


> What I'm wondering is actually "which digicam most
> closely
> approximates an old Leica in B&W?"  In other words,
> discrete /
> fast-responding / optically excellent. 
> 


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--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Phil Rose"
<pjrose@f...> wrote:
> So--go easy on the blue channel (which is common practice anyway
> because of noise issues).

I find the blue channel next to useless for many if not most
conversions.

F_P