Digital BW, The Print

Sorry for some ignorance.... what's ARC?

On Tue, Aug 9, 2011 at 5:31 AM, Ernst Dinkla <edinkla@...>wrote:

> **
>
>
> On 08/07/2011 05:54 PM, Lew Schwartz wrote:
> > If I understand the problem of aliasing correctly, it results from a
> > phenomenon similar to the one encountered in the darkroom with diffuser
> vs
> > condenser light sources on the enlarger and, if this is the case, a
> diffuser
> > may well be the answer. Since the 5000 has an auto frame advance
> mechanism
> > to deal with, however, I don't think this would be very easy.
>
> The enlarger light sources differ on the Callier effect in the film
> emulsion which is a kind of diffraction on the spaces between the film
> grain. There might be something of that Callier effect happening in the
> Nikon scanner too but it is likely more complex. There is little
> oversampling done in the Nikon scanner, the sampling rate comes close to
> the delivered resolution. In flatbed models like the Epson V700 the
> sampling rate is much higher than the actual resolution the scanner can
> deliver (based on the sensor well sizes, well pitch). Several sensors
> are shifted half the pitch width in both directions. More samples made
> with bigger sensor well sizes average the readings and noise is reduced
> that way. Do not expect the resolution to be equal to the sampling
> rate. That oversampling has an analogy to the use of a wider aperture in
> drum scanning for grain reduction.
>
> In practice I can not avoid aliased grain on my Nikon 8000. Nevertheless
> I do not go the route to reduce grain by making the light more diffuse
> or with a small focus shift. Software like Neat Image can do a good job
> in suppressing aliased grain if I can define the aliased grain as good
> as possible over the frame size. Wet mounting of the film is one step,
> tweaking the film holders to get exact focus on all spots the next step.
> I checked using only the green or blue LEDs for the B&W scan. Vuescan's
> analogue gain sliders allow that: the channel used at 2x, the other two
> taken out, RAW histogram to check whether there is enough exposure. DNG
> export. Further processing in ARC and Photoshop + Neat Image.
> The blue light shifts the grain aliasing a bit on the tone range
> compared to green light but is not noisier in my experience. In theory
> the shorter wavelength blue light should show less diffraction between
> the grain particles if the grain aliasing is partly caused by the
> Callier effect. So far I used ARC's noise reduction very modest to
> remove noise from the positive highlights (actually then still the dense
> part of the digital negative) and in Photoshop Neat Image to reduce it
> in the positive shadows. Still not sure about sharpening, I think
> Photoshop's smart lens sharpening does it better and I should not use
> ARC's tools for it. ARC is typically more made for digital imagers while
> Photoshop still is a mix of tools suitable for both. All in all I can
> reduce noise and keep detail better than with the methods before.
>
> In contrast with selecting one channel from a normally full RGB LED
> lighted scan the focusing in the scanner is also done with the single
> LED color so optimal for that light. I also think that it should reduce
> flare in the optical path and more optical artefacts that an RGB
> lightsource could create in the channel that is selected from a normal
> B&W scan. This method has some analogy to the use of single band/UV rich
> enlarger light in large format B&W photography. The neon A4+ cold light
> that I had made for graphic arts films must be on the attic somewhere
> but I did not forget the principles. Of course I checked what kind of 9"
> CCFL tubes are available with a blue light to make a B&W flatbed. There
> are some with a spectral peak around 457 NM, most likely right in the
> middle of the blue sensor sensitivity.
>
>
> --
> Met vriendelijke groeten, Ernst
>
> Try: http://tech.groups.yahoo.com/group/Wide_Inkjet_Printers/
>
> | Dinkla Grafische Techniek |
> | www.pigment-print.com |
> | ( unvollendet ) |
>
>  
>


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