Re: [Leica] Things that go bump in the night (very long). Up

[Peterson_Art@hq.navsea.navy.mil]

     WOW!  Thank you, Jim!  I have no way of knowing---have no clue---if 
     all this is right or wrong, but damn!, it sure is impressive.  You've 
     obviously put a lot of effort into this explanation, and gratitude is 
     certainly due.  Thanks again,
     
     Art Peterson
     

______________________________ Reply Separator _________________________________
Subject: [Leica] Things that go bump in the night (very long). Update
Author:  leica-users@mejac.palo-alto.ca.us at Internet
Date:    2/5/99 10:32 AM


For those that are interested. This is pretty much generalized so please 
don't pick at me about details. I've kept it general, mainly because 
anything more detailed would detract from the point. I do not claim to be 
an authority on all of this. It came from both the work I am doing at Photo 
Access and from my reference library. And again, it's generalized for 
understandability.
     
These are averages, not specifics.
     
Sizes:
     
1 micron = size of a cell nucleus
.1 micron = strands of DNA
.01 micron = structure of DNA
.001 micron = DNA molecule
.0001 micron = 1 Angstrom
1 Angstrom = Carbon's outer electron shell 
wavelength of visible light = 4000 to 8000 Angstroms
     
Current semiconductor chip geometry = .18 micron
It could possibly go to .1 micron. The size of DNA strands. 
The average wavelength of light is 6 microns.
     
How many of you remember when the Electron Microscope was invented. The 
reason it was invented was because visible light and optics had reached 
their limit. Visible light got in it's own way. So going to the atomic 
level, inventing a Scanning Electron Microscope, eliminated the visible 
light/optics limit.
     
So at less than .1 micron, semiconductors will be stumbling over their 
molecular structure. And the wavelength of light requires certain 
dimensions in order to pass the ray and not cut it off like a filter. A 
polarizer, I believe, works at around 1.5 microns. These phenomena place 
size constraints on semiconductor junctions (such as photo transistors, AKA 
a pixel) and the light gathering "bucket" (a capacitive junction), and of 
course attempting to read-out the minuscule signal representing a pixel.
     
The following discussion about the latent image is a high level overview. 
It by no means is definitive. Libraries are filled with volumes of the 
physics and chemistry of the latent image and development. The point being 
made here is that the silver image is produced at the atomic level. Atoms 
and electrons.
     
To put things in perspective, the volume of an "average" silver halide 
grain is .0000000000001 cubic cm. Within the 10**-13 cubic centimeter grain 
of silver halide, there are 10 billion silver halide molecules. Exposure is 
affected by a photon hitting a silver halide molecule. This causes 
electrons, within the molecule, to change from a stable to an unstable 
energy level, leaving an electron deficiency in the lower level. 
Development is accomplished by allowing an electrolyte with redox potential 
(developer) to contact the silver halide crystal. An electron from the 
developer moves into the vacancy left by the electron that moved because of 
the photon hit. When the new electron moves in, the overall charge of the 
crystal is negative (because of the added negative electrons.) To 
compensate for the increased negative charge at the latent image site, 
positive charged interstitial silver ions move into the sites, neutralizing 
the charge. If enough photons hit the silver halide grain, enough electrons 
will move from the developer into the grain, which allow the formation 
silver atom aggregates. This is your image forming.
     
In digital photography, a semiconductor capacitor stores the electrons 
(supplied by a battery) that a photo transistor allows in. The number of 
electrons stored will depend upon how much light hit the photo transistor, 
and for how long. Think of the photo transistor as an electron gate. The 
stored charge will be a "voltage level." This voltage (at each individual 
pixel site) is then applied to an analog to digital converter (A to D). The 
output of the A to D is a number between 0 and 255, representing the amount 
of light hitting the pixel. And don't forget, these pixels are read out "one 
at a time". All one, two, four, or six million of them.
     
So now, in digital, we have 256 possible density levels, at a site that is 
at least 5 microns by 5 microns square. While in film, we have a grain site 
that has 10 Billion molecules. If it takes 1,000 silver atoms to produce a 
developed "speck" on the film, we have 10,000 possible density/size levels 
producible at a silver grain site. If it takes 10,000 silver atoms to 
produce a developed "speck" on the film, we have 1000 possible density/size 
levels producible at a silver grain site. All done at the atomic level. 
Without batteries, capacitors, transistors, A/D's, wires, megabytes of 
memory, gigabytes of storage, etc...
     
There's more. Each pixel in a digital sensor, sees light a little 
differently than its neighboring pixel. If you took a photograph using a 
raw sensor, it would look awful. In a good digital camera, "each" sensor 
has to be calibrated. We have to test and "record" how each pixel differs 
from a normal pixel. This is called PRNU (Photo Response Non Uniformity) 
correction. Cheap digital cameras (under $2000) use only "white balance" 
and approximately adjust each pixel's output with regard to white. Good 
digital systems use PRNU correction. The PRNU correction table for a 2 
megapixel sensor, without PRNU compression, is six megabytes. So your 
professional digital camera has to have six to twenty megabytes of memory 
available just for pixel correction. This correction has to be done, on the 
fly, as pixels are streaming out of the sensor, into memory.
     
Many digital cameras use sensors that have bad pixels. It is very difficult 
to make a large (35mm size) sensor without faults. That's why most consumer 
cameras use very tiny sensors and 10mm to 15mm lenses as the normal lens. 
The process of fabricating a large sensor is extremely complex and full of 
problems. As it is with any large semiconductor "chip". Good large sensors 
are very expensive to make and expensive to purchase. So bad pixels must be 
handled in the camera. Algorithms that give weighted averages to "previous" 
pixels go into forming a density value for the bad pixel. We can only use 
"previous" pixels because this process works as the pixels stream in, and 
the only known values are from "previous" pixels.
     
Since a digital image is simply samplings of the subject, at precise points, 
fine patterns in the subject will be recorded incorrectly. The digitizing of 
anything has a "nyquest" sampling boundary where the frequency of the source 
(subject) interferes with the digitized output. Think of using a digital 
sensor for astronomical photography. Two distant stars, side by side, that 
happen to focus on adjacent digital pixels. The digital system will see them 
as a single elongated spot. Not two distinct spots, or stars, as they would 
appear on film. Going from analog to digital in any discipline, causes 
problems that didn't exist before. The real world is an analog world. 
Anytime you digitize any analog representation, something will be lost. 
That's the physics of A to D. As the sampling rate increases, the 
representation of the analog source is more true. Unfortunately, the 
sampling rate in a digital sensor is simply how closely packed and how small 
the pixel sensors can be made. Well... the physics of semiconductor 
manufacturing, pretty much establishes the rules. And we are up against the 
wall.
     
So... my feeling is that the "technological breakthrough" that will propel 
digital photography into the forefront, will be nothing that we (lay 
people) are familiar with today. It will have to be the ability to 
electronically control molecular bonds or electron orbits, and perhaps have 
a build-up of, or depletion of, tagged electrons that can be read-out, 
perhaps radiometrically, in parallel. But your guess is as good as mine.
     
Going to the level of actually competing with film will require a very very 
major breakthrough in electronic pixel recording. This is going to take a 
long time by anyone's standards. The saying of "every year half the cost 
and twice the performance" works only over a finite time. Just like optical 
microscopes. Just like propeller engines. Just like electronics. You can 
only go so small and so fast for so long. And then you hit the wall. And 
have to "invent" some new grandiose scheme. We are pretty close to that 
wall in digital photography.
     
Digital photography is "different" than film photography. The whole 
process, from front to back, is near the wall. It takes massive files to 
store digital images at full resolution. Lossless compression has been 
worked on, by wizards, for decades. Anything other than a little 
compression, will degrade the image. Moving, storing, and portability of 
digital images is a also a major headache. Requiring lots of CPU 
horsepower. The whole discipline requires lots of money.
     
Digital photography, as we know it now, produces outstanding results for 
the disciplines for which it is matched. Consumer P&S, catalog photography 
& production, and news photography. But for sheer recording superiority, 
information content, ease of use, easy storage, highly portable, easily 
viewable, comparatively inexpensive (unless you are a Leica user!), very 
inexpensive (pinhole photography), comes in a little can with no wires 
attached, and can be digitized after the fact producing superior digitized 
results, it is "film". Can you choose between digital sensor "types"? High 
speed low res, Low speed hi res and all in between? Color? B&W? No. You 
have to use film, or buy a different type of digital camera. One matched to 
each type of photography you want to do.
     
So until the breakthrough (don't hold your breath)... I'm a Leica kinda guy!
     
I Lika Leica
     
Jim