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"Brightening" of processed Ektachromes


robert_a._zeichner

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Well, it's not often that I expose color film, but once in a great while I do and over the years I've collected a handful of slightly underexposed EPN's. A friend showed me a kit he bought from Edwal that was designed to brighten underexposed Kodachrome. He said they also made a kit for Ektachrome, but I have not been able to find info about that on Edwal's web site. I don't need more that about a half a stop of "brightening" in most instances. Any of you chrome experts out there have any ideas? Is there some secret supplier who sells this stuff? Is this one more environmental "worst nightmare" that has been banned? Your input will be appreciated.
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Another vote here for scanning and, possibly, re-outputting to

film.<br>The 'reducers' for colour slide are a bit hit-or-miss. They

consist of bleaches for the three CMY dye layers individually, so the

mix of chemicals is pretty critical. I know that one of the chemicals

used is common household bleach; sodium perchlorate; for the magenta

layer if memory serves. The other two aren't particularly exotic as I

recall, but getting the mix right needs a lot of trial and error

experimentation.

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Ed Degginger invented the Kodachrome formula that lightens

underexposed chromes. He spent his career as a chemist and was

always an avid 35mm photographer (lots of wildlife, though much

general stock too). It is/was a two-bath system that 1)bleaches and

2)stops the bleaching. He sold it to Edwal and now sells stock out of

Morristown, NJ. I found that it always made chromes magenta. It hit

successive layers of dyes in the film, the magenta being the last.

You had to stop the bleaching fast to save it, but that left a

preponderance of magenta and increased contrast. Some of my attempts

were quite good, others not so good. I heard that Edwal came out with

a similar chemical for E-6 but I don't know this to be true. Digital

manipulation would seem to be the way to go these days. But Edwal is

part of Falcon Safety Products in NJ, and they probably have a Web

site and do have an 800 number. They are helpful and responsive.

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Modifying electronically an underexposed slide means that you have to use a very high performance scanner with a

D-Max of 4.2 or more. Otherwise the image you will get is likely to be lacking depth in the shadows. I also have a

bunch of nice but underexposed slides (mostly Velvia). My scanner is not capable of reaching into the darkest areas

to restitute enough details. I wondered if the best way to salvage them would not be making duplicates on low

contrast film? A friend of mine showed me how he pulled color from a nearly black Kodachrome duplicating it with a

sandwiched contrast mask. I was amazed! I used to make the masks for lowering the contrast of Ilfochrome prints,

with Kodak Pan Masking, but I am not familiar with duplicating slides.

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Deviating a bit into scanner-land...

 

<p>

 

Pete Andrews' point (that Dmax for EPN is fairly low) is technically

correct, but from a practical standpoint I think that Paul

Schillinger's advice is still good: If you want to lighten, you would

do well to find a scanner with the widest dynamic range possible.

 

<p>

 

Although many scanners have rated Dmax well in excess of 3.3, very few

can actually extractl noise-free detail from something that dark. My

experience is that scanner Dmax ratings tend to be inflated by 0.5-1.0

units of density relative to what they can actually handle witho0ut

perceptible noise. If you really want to fetch all of the shadow

detail possible out of a piece of film with a Dmax of 3.3 or 3.76,

then a scanner with a rated Dmax of 4.2 would probably be the

appropriate tool for the job.

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Pete, thanks for correcting me, although I think you are right and you are wrong. I'm not a specialist but I have

soon discovered the limitations of the electronic tools I'm using. Often scanner constructors have a

questionable way of putting up the specifications for their products. For one it would be that the scanner is

capable of producing sharp details and differentiated colors into the D-Max and for others that they will be

able to catch some light and produce a muddy gray in the same density. Both would boast a D-Max of let's say,

4.0 but when you compare the resulting scans from a scanner costing 3 K and from one costing 30 K, you will

soon discover what makes the difference. I am personally convinced that it is not necessary to spend a

fortune to get a good scanner, but then there are some limitations one has to put up with. Another precision is

about density range, which is not to be mixed up with D-Max. A correctly exposed slide has a density range of

3.3 or 3.7, which is the density range most good scanners can analyze. But when a slide is underexposed, the

density range can be the same, but the overall and Maximum Density are considerably augmented and this is

where you have to use a "beast" to get the colored pixels out of the film. Otherwise, the dark areas will just

be "dull black".

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Yes. It's a complicated issue Paul, and I agree that a lot of low-end

scanners have ideas above their station when it comes to dynamic

range.<br>The ability to pull shades of dark grey up to mid tones is

more a function of a scanner's bit depth and the programmability of

its 'gamma' curve, as well as its inherent noise, rather than the

actual Dmax that it can 'see' down to.<br>Most scanners could, in

fact, see a higher density, simply by winding up the intensity of the

lamp; but if it was that easy, then we'd have even more ridiculous

claims from scanner manufacturers than we have already.<p>

The problem's compounded by the fact that the film's RGB curves

flatten out and separate widely after 3.0D or so, and this is another

good reason to go the scanner route, as this can be partially

corrected in sofware, but not by chemical bleaching.<br>Ektachrome

appears to have less separation than Kodachrome or Velvia from its

characteristic curves, but in real-life it always seems to get the

blues in the shadow areas.

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Pete, to illustrate what we are talking about, I have two scanners. One is a 7 years old drum scanner, dynamic range

and D-Max are 3.6, 12 bits color. The other one is a recent flatbed boasting 3.7 dynamic range, 4.2 D-Max and 16 bits

color depth. This is not a very expensive scanner (a little more than 3K) but you would think it is better than the

previous. Not at all! I made comparison scans and the drum has far better picture quality in the dense areas despite

it's modest specs. The flatbed is quite comparable when it stays within well exposed films, with perhaps a little more

USM needed to achieve the same "optical" sharpness. It's 16 bits differenciates millions of colors but as they will be

compressed to the 8 bits of Photoshop, you will hardly see the difference from the 12 bits scanner anyway.

 

<p>

 

But, I agree, scanning a dark slide is certainly the best an easiest way to correct it.

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Pete Andrews wrote:

 

<p>

 

> Most scanners could, in fact, see a higher density, simply by

winding up the intensity of the lamp

 

<p>

 

This is untrue for most scanners, unless you're willing to allow the

CCD's analog output to saturate in mid- and light-tones. If you turn

up the lamp, then you'll simply end up shortening the integration time

(the amount of time between transfer gate signals) to stay under

saturation. Provided that the integration time was reasonably short to

begin with, this puts you right back where you started in terms of

maximum density.

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What I said about 'turning up the wick' is absolutely true Patrick. I

didn't say it would increase the dynamic range, or that it wouldn't

have any other deleterious effect. In fact, I went on to say that it

wasn't that simple.<br>Why do you assume that I was only referring to

CCD scanners? PM based drum scanners don't saturate easily, and some

of them actually use lamp intensity to control exposure.<p>Paul, the

bit-depth of a scanner is more important for maintaining a linear

relationship between density/brightness and the digital output, than

in capturing more colours. Greater bit depth <i>should</i> also allow

more flexibility in mapping the tone curve to an 8 bit output, but if

the scanner is CCD based then the limitation is probably with the

sensors, rather than the rest of the circuitry. Most CCDs have a

dynamic range of 4 or 5 thousand to 1, about 3.6D in terms of density,

or 12 bits in digital terms. Feeding this into a 16 bit A/D won't

improve this basic limitation, and that's why your high-end flatbed

still can't beat your mid-range drum scanner.<br>The real bottleneck

these days is that damned 8 bit per channel output. I think if we can

make 16 bit the norm, then desktop scanner makers will be prodded into

doing some catching up.<br>Anyway this is all way off topic. Sorry!

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"I think if we can make 16 bit the norm, then desktop scanner makers will be prodded into doing some catching up."

Pete, not long ago, this would have seemed a ridiculous expense of megabytes. But now, with the super-computers

being brought to the desktop at a low price, new huge and cheap harddisks (Ultra ATA 66+) and affordable memory,

this norm, already partly supported by Photoshop and some scanners is at hand. Still, output machines and monitors

have to be updated.

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