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Could you actually see photos made from RAW files?



 
 
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  #51  
Old June 3rd 09, 03:36 AM posted to rec.photo.digital,uk.rec.photo.misc
Eric Stevens
external usenet poster
 
Posts: 13,611
Default Could you actually see photos made from RAW files?

On Wed, 03 Jun 2009 11:51:59 +1000, Bob Larter
wrote:

Eric Stevens wrote:
On Tue, 02 Jun 2009 02:09:19 -0800, (Floyd L.
Davidson) wrote:

[...]
The definition of "analog" is that the signal (in this
case it would be the output signal from the sensor) is
continuously variable (it has an infinite number of
possible values). If it is "digital" then it must have
a finite set of discrete values. (Note that the two
definitions are together all inclusive and are mutually
exclusive. Everything is either one or the other and
nothing can be both.)


Haw. You are now claiming that it is possible to have a continuously
variable number of electrons. I maintain the number of electrons can
only be represented by integers.


By that exact same logic, resistors capacitors & transistors should be
called "digital" devices, but they aren't. The industry definition of
"digital" is something that only works with binary levels. Everything
else is called "analog".
References:
http://en.wikipedia.org/wiki/Digital_electronics


"In a digital circuit, a signal is represented in discrete states or
logic levels." - but they don't have to be binary.

http://en.wikipedia.org/wiki/Analog_electronics


"Any change in the signal is meaningful, and each level of the signal
represents a different level of the phenomenon that it represents."
This isn't the case with the output from a charge amplifier. 0.050,000
volts represents 50,000 electrons. 0.050,000,4 volts still represents
50,000 electrons. But 0.050,001 volts represents 50,001 electrons as
does 0.050,000,6 volts.

In summary:
---
Analogue electronics (or analog in American English) are those
electronic systems with a continuously variable signal. In contrast, in
digital electronics signals usually take only two different levels. The
term "analogue" describes the proportional relationship between a signal
and a voltage or current that represented the signal.

" ... _usually_ take only two different levels." But what about Rambus
XDR memory which uses three different levels? Two levels are used
because they are the simplest.

In the case of an image sensor, the output voltage is an analog to the
light level that impinges upon it.


It still has to be capable of accurate digitisation and to that extent
it is digital.



Eric Stevens
  #52  
Old June 3rd 09, 06:48 AM posted to rec.photo.digital,uk.rec.photo.misc
Floyd L. Davidson
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Posts: 5,138
Default Could you actually see photos made from RAW files?

Eric Stevens wrote:
On Wed, 03 Jun 2009 11:37:23 +1000, Bob Larter
wrote:

Eric Stevens wrote:
Are you really saying that a given RAW data file can be created by
more than one image?


Yes. If you think carefully about how an image sensor works, it's obvious.


I may be missing something but its not obvious to me.

A lens directs light from a scene so as to form an image on the
camera's sensor.

Different parts of the image fall on individual sensels which, in the
time allowed to them, capture photons which generate electrons. The
accumulated electrons form an electrical charge in each sensel.


Is there any reason to believe that the same scene would
necessarily produce the same effect on the sensor every
time? In fact, the light is not represented by a
steady, consistent flow of photons. The photons arrive
at irregular intervals. It's called "photon noise".
The effect is that if the same image is projected onto a
sensor, each time the sensor is read the image will be
recorded with unique data that is not identical to the
other times that image is recorded.

According to the type of sensel, the charge is 'read' in one way or
another, and the quantity of charge converted to digital data.


Whoops, you just skipped over an awful lot of very fancy technology.
The data from the sensor is analog data. The process by which it
is converted to digital data is a one way process that cannot be
reversed with accuracy. I've gone into detail on that in another
article previously and will not repeat it at length here.

The digital value of the charge is saved in an array which enables the
value of the charge for each individual sensel to be mapped to the
position of the sensel.


So it is true that the position is relevant.

Leaving out the question of whether or not the data is further
massaged by the camera before-hand, the data array is saved as the RAW
data file for the image.


Okay.

That original image on the sensor is characterised by by the raw data
array. Any change in the image gives rise to a different data array.


Not necessarily. How significant the change is is what
determines whether it changes the raw data. Some
changes simply are not great enough to cause any
difference in the data set.

As far as I can see only the one image can give rise to a particular
data array.


Clearly that is not true.

I would be grateful for an explanation of how a different image can
give rise to the same data array.


You've been given several.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)
  #53  
Old June 3rd 09, 07:00 AM posted to rec.photo.digital,uk.rec.photo.misc
Floyd L. Davidson
external usenet poster
 
Posts: 5,138
Default Could you actually see photos made from RAW files?

Chris H wrote:
In message , Floyd L. Davidson
writes
Everything is either one or the other and
nothing can be both.)


This is not correct. There are plenty of mixed devices about. Analog
Devices make a few of them.


You can have a complex device that has, for example, an
input that is one and an output that is another. But
you cannot have a signal that is both. "Everything"
means an atomic device, not a complex device. (My
apologies, I wrote the above expecting common sense
readers who understood the context.)

That is *not* part of the firmware. Firmware, other
than setting the ISO gain, has no part in any of that
other than turning it on and off.

You are referring to 'firmware' as though it was 'hardware'. Yet Nikon
can program the camera to behave differently so some software/firmware
must be involved.


Perfectly correct.


That does not cause hardware to become firmware.

I am referring to that as hardware because in fact it is
hardware. It is not done with software/firmware.


Yes it is. What is more I can supply the tools to write the firmware.


So you think the analog amplifiers and the ADC are
firmware and can be done with software tools??? That's
a bit of abject ignorance.

It's done with hardware.

(I can't tell you which but We have supplied software/firmware tools to
more than one OEM digital camera company (P&S variety)


Not for those functions you haven't.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)
  #54  
Old June 3rd 09, 08:00 AM posted to rec.photo.digital,uk.rec.photo.misc
Floyd L. Davidson
external usenet poster
 
Posts: 5,138
Default Could you actually see photos made from RAW files?

Eric Stevens wrote:
It can be OK for you to do that if you indicate that that is what you
have done. But you don't do that. You just delete blocks of text. This
can result in me appearing to say something other than what I actually
said. It can also result in the deletion of the explanation and
justification of what I did say.


It doesn't. What you said remains in the original post
for all to read. I quote just enough to refresh a
reader's memory on what it was. That has *always* been
the standard practice on Usenet, though in recent years
there have been many many fools who cannot understand
how to write concisely nor accurately. But your lack of
ability to do so is not a cause for me to take on the
same poor style that you use!

You can't claim that you don't know any better than this if only for
the twenty years of experience you have had with Usenet. What you have
been doing would not have been tolerated for one second twenty years
ago (yeah - I was there too).


Can I assume you didn't have a clue then either?

See http://www.softdevlabs.com/personal/Usenet101.html

"Please remember that when you do snip portions of a person's
post, it's extremely important that you not only indicate that
you've done so, but also where you've done so. [5]

The commonly accepted way to indicate snips is to simply insert
the string "snip" (or similar notation) on a line by itself at
the spot where the deleted text used to be. "


You saw it on the Internet, so it must be true. Sheesh.
Cite an authoritative source. (Actually, I'll challenge you
to find anything at all from 20 years ago that says anything
like that.)

Okay, you don't know what an analog device is, so lets go
over that too.

The definition of "analog" is that the signal (in this
case it would be the output signal from the sensor) is
continuously variable (it has an infinite number of
possible values). If it is "digital" then it must have
a finite set of discrete values. (Note that the two
definitions are together all inclusive and are mutually
exclusive. Everything is either one or the other and
nothing can be both.)


Haw. You are now claiming that it is possible to have a continuously
variable number of electrons. I maintain the number of electrons can
only be represented by integers.


So what? That makes the number of electrons digital.

But we aren't actually measuring the number of electrons,
are we? We are measuring the current that flows as a
result of the charge that was stored (which is roughly
proportional to the number of electrons). The current
that flows is affected not only by the number of
electrons, but how fast they move and which direction
they go. Both of those characteristics are continuously
variable.

And hence electric current is analog, and so is voltage.

Now, you may notice that the output of the sensor is a
voltage which is continuously variable over an infinite
number of values between 0 and 1 volts. That makes it
an *analog* device by definition.


The output of the sensor is an electrical charge.


Actually it is a current flowing into the input
impedance of an amplifier, and thus producing a voltage.
The amplifier is affected by the voltage, which is an
analog parameter.

The electrical
charge is dumped into a charge amplifier and it is this which outputs
the voltage. This is the first step in transforming sensor image into
the RAW data file.


And it is clearly an all analog process.

That analog data is fed into a device that converts it
to digital data.


The output of the charge amplifier is then digitised. This is the


Actually it is a voltage amplifier.

second step in transforming sensor image into the RAW data file.


Well, actually it is then run through ISO amplifiers,
but we could ignore those is you like.

The output has a finite set of
discrete values. If, for example, it is a 12-bit
digital signal then there are as many as 4096 values.


In the case of the Nikon D300 the RAW file can be output as either 12
bit or 14 bit. It is likely that before it can be transformed into
either of those formats it is processed in the camera in some other
format.


Why is that likely? That is what the output of the ADC
is, and all that necessarily happens after that is the
data stream is read by the CPU so that it can be written
to the file.

These values are not continuous (i.e., 3 and 4 are
discrete and there are no values between them as there
would be for an analog signal), hence they are discrete,
and the signal is by definition *digital*.


Before it hits the RAW file, the data is further massaged.


For several paragraphs now your comments have had
absolutely nothing to do with the text you are quoting.

What's your point?

The reason I've been stating that there are many
possible images which can produce the same digital data
set is because the analog signal to produce any single
one of those 4096 values has an infinite number of
possible values.


Not so.


Claim that all you like, but it is true.

The digital value of say 1612 corresponds with only one state
of the particular sensor element.


False. It corresponds to a range of values. Because
the range is analog, there are an infinite number of
possible values in that range.

After the data is digitized, it has one value (1612) and
you cannot determine which of the infinite number of
analog values that could be 1612 it actually was to
start with.

If you know the chain of
transformations between the sensels and the corresponding data of the
RAW file you can work it backwards to derive from the RAW file the
state of the individual sensels which gave rise to the data in the
first place.


False.

The reason I've said you cannot precisely restore the
original image on the sensor is because you do not know
exactly which of the infinite number of possible values
for each digital value should actually be used for the
analog image.


But you do if you understand the nature of the transformation.


No, if you understand the nature of the transform then
you realize that exactly the opposite is true. The
digital value of 1612 might, for example, represent a
range of voltages between .25 and .30 volts. When you
look at the digital value of 1612, you cannot determine
if it was .26675382, or .28778391. All you know that is
was between .25 and .30 volts.


Basic information theory. (Ever heard of Claude E. Shannon??)


Of course I have. What exactly does he have to do with it?


Everything.

He more or less defined all of it with mathematics, and
analyzed what it meant. Because of his work it was
decided that the telecommunications industry would
benefit from moving to a digital network and abandon
the analog network. It was also clear that digital
imaging would be much much preferred to analog imaging.
That is why inventions which appeared to be useful for
digital photography were developed instead of ignored,
even though there was no market at all for them at the
time.

I am referring to that as hardware because in fact it is
hardware. It is not done with software/firmware. This
is much like the way you insisted for article after
article that the RAW data had been interpolated...


You had led me onto the garden path for that one.


You are the one who takes these hikes into fantasy land
Eric, not me. We are discussing a topic that I've been
working with for literally decades, and one that I'm
familiar with down to the bit diddling level. I may not
always be able to describe things in a way that every
given individual can understand clearly, but with help
from the individual I can eventually find it. The
problem here is that while I clearly do understand all
of this extremely well and you don't, you won't help
with learning it.

Nevertheless there
is software between the formation of the image on the sensor and the
writing of the data to the RAW file.


But that software is *not* image manipulation software.
All it necessarily does is encode the data so that it can
be written to a standard file format.

That is why/how various problems
(e.g. vertical stripes) can be cured by a firmware upgrade.


That sounds more like the image manipulation that is done
to the JPEG conversion, not to raw data. Regardless, it
would also be possible to introduce banding by dropping
data bits or whatever as the data is encoded for writing
to a file. That is *not* image manipulation software, and
correcting it with a firmware upgrade does not support
your arguments.

The original argument was over whether or not it was possible to work
back from the RAW data and arrive at more than one sensor image. I

A nonsense idea, but...


Its not at all nonsense, even if you think it is so.


Except for one little problem: you can't do it. (That, as I
and everyone except you seems to realize, makes it nonsense.)

See
http://www.clarkvision.com/imagedeta...mance.summary/
for a better indication of the number of electrons you can expect to
deal with: 50,000 or more.


The little guy standing there looking into the well and
counting those electrons might be digital, eh?

But since what cameras do is discharge the device
through an impedance and amplify the voltage, we don't
have a digital count of electrons, we have an analog
signal indicating how much charge there was. Of course
it includes noise, so even if we did know the exact
analog voltage (which as has been show, we cannot), we
still wouldn't be able to determine how many electrons
were actually captured.

Unless you happen to know that digital guy there
counting them, and he doesn't run away because of your
tin foil hat. Or some other nonsense...

article. It isn't rocket science. But it *is*
something I've been dealing with for 40 years now...
and hence it is not at all surprising that I might
understand it rather well and can explain it in 15
different ways. But it does make all of your petty
insults a bit of a joke, Eric.


Congratulations! 40 years ago you were working in Bell Labs along with
Boyle and Smith! And I thought you were only a psychologist.


Well, I didn't ever work at Bell Labs, but in fact I did
work for AT&T. The telecommunications industry of
course has been vitally interested in exactly this
business of digital vs analog data roughly since the
1930's in this context.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)
  #55  
Old June 3rd 09, 08:17 AM posted to rec.photo.digital,uk.rec.photo.misc
Floyd L. Davidson
external usenet poster
 
Posts: 5,138
Default Could you actually see photos made from RAW files?

Eric Stevens wrote:
On Wed, 03 Jun 2009 11:51:59 +1000, Bob Larter
wrote:

Eric Stevens wrote:
On Tue, 02 Jun 2009 02:09:19 -0800, (Floyd L.
Davidson) wrote:

[...]
The definition of "analog" is that the signal (in this
case it would be the output signal from the sensor) is
continuously variable (it has an infinite number of
possible values). If it is "digital" then it must have
a finite set of discrete values. (Note that the two
definitions are together all inclusive and are mutually
exclusive. Everything is either one or the other and
nothing can be both.)

Haw. You are now claiming that it is possible to have a continuously
variable number of electrons. I maintain the number of electrons can
only be represented by integers.


By that exact same logic, resistors capacitors & transistors should be
called "digital" devices, but they aren't. The industry definition of
"digital" is something that only works with binary levels. Everything
else is called "analog".
References:
http://en.wikipedia.org/wiki/Digital_electronics


"In a digital circuit, a signal is represented in discrete states or
logic levels." - but they don't have to be binary.


What's your point? Binary is necessarily digital, but
digital is not necessarily binary (though any value that
is digital can necessarily be encoded in a binary form).
Got that?

The point is still that while the number electrons on
the head of a pin might be discrete, the current
produces by the flow of those electrons is *not*
discrete, and therefore is analog.

Of course the output of an electronic sensor in a camera
is the analog current, not the discrete number of
electons capture.

http://en.wikipedia.org/wiki/Analog_electronics


"Any change in the signal is meaningful, and each level of the signal
represents a different level of the phenomenon that it represents."


That is correct. Any change is meaningful on the
*input* to whereever the signal goes. It does *not*
necessarily mean it somehow is meaningful to anything
else (such as the number of electrons that cause the
signal to exist).

This isn't the case with the output from a charge amplifier. 0.050,000
volts represents 50,000 electrons. 0.050,000,4 volts still represents
50,000 electrons. But 0.050,001 volts represents 50,001 electrons as
does 0.050,000,6 volts.


Is that supposed to make sense?

The output from the amplifier is an analog signal.
Anything you thing means otherwise is nonsense. If you
doubt that, explain how and why it is fed to an analog
amplifier and then to a device called an
Analog-to-Digital-Converter.

In summary:
---
Analogue electronics (or analog in American English) are those
electronic systems with a continuously variable signal. In contrast, in
digital electronics signals usually take only two different levels. The


That isn't really true, about "signals usually take only
two ...". In fact the entire digital Public Switched
Telephone Network (PSTN), as well as virtually all of
the music and video that is digitally recorded, uses
what is called an m-ary level encoding. In most cases
that is a 255 level PCM digital signal.

term "analogue" describes the proportional relationship between a signal
and a voltage or current that represented the signal.

" ... _usually_ take only two different levels." But what about Rambus
XDR memory which uses three different levels? Two levels are used
because they are the simplest.

In the case of an image sensor, the output voltage is an analog to the
light level that impinges upon it.


It still has to be capable of accurate digitisation and to that extent
it is digital.


That statement is pure nonsense. It doesn't "have to be
capable of accurate digitisation", whatever it is that
you think that means. It is not digital in any way
until it *is* digitized.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

  #56  
Old June 3rd 09, 10:40 AM posted to rec.photo.digital,uk.rec.photo.misc
Eric Stevens
external usenet poster
 
Posts: 13,611
Default Could you actually see photos made from RAW files?

On Tue, 02 Jun 2009 21:48:52 -0800, (Floyd L.
Davidson) wrote:

Eric Stevens wrote:
On Wed, 03 Jun 2009 11:37:23 +1000, Bob Larter
wrote:

Eric Stevens wrote:
Are you really saying that a given RAW data file can be created by
more than one image?

Yes. If you think carefully about how an image sensor works, it's obvious.


I may be missing something but its not obvious to me.

A lens directs light from a scene so as to form an image on the
camera's sensor.

Different parts of the image fall on individual sensels which, in the
time allowed to them, capture photons which generate electrons. The
accumulated electrons form an electrical charge in each sensel.


Is there any reason to believe that the same scene would
necessarily produce the same effect on the sensor every
time? In fact, the light is not represented by a
steady, consistent flow of photons. The photons arrive
at irregular intervals. It's called "photon noise".
The effect is that if the same image is projected onto a
sensor, each time the sensor is read the image will be
recorded with unique data that is not identical to the
other times that image is recorded.


This is certainly a problem at low light levels but, by and large,
this is what I meant by "statistical error limitations". When you get
to this level you are in danger of introducing quantum theory.

According to the type of sensel, the charge is 'read' in one way or
another, and the quantity of charge converted to digital data.


Whoops, you just skipped over an awful lot of very fancy technology.
The data from the sensor is analog data.


The sensel counts photons which it converts to photons. The data is
integer. This is converted to binary digital data. You might say it is
encoded. I would say it is transformed. It doesn't matter which either
way.

The process by which it
is converted to digital data is a one way process that cannot be
reversed with accuracy. I've gone into detail on that in another
article previously and will not repeat it at length here.


You should, if you want me to know what you are talking about. But of
course the 'transformation' can be run backwards, even if you don't
use the same hardware. Its the algorithm you have to reverse.

The digital value of the charge is saved in an array which enables the
value of the charge for each individual sensel to be mapped to the
position of the sensel.


So it is true that the position is relevant.


Whoever argued otherwise?

Leaving out the question of whether or not the data is further
massaged by the camera before-hand, the data array is saved as the RAW
data file for the image.


Okay.

That original image on the sensor is characterised by by the raw data
array. Any change in the image gives rise to a different data array.


Not necessarily. How significant the change is is what
determines whether it changes the raw data. Some
changes simply are not great enough to cause any
difference in the data set.


Changes are quantized. A different image on the sensor gives a
different number of electrons which are transformed into different
digital data.

As far as I can see only the one image can give rise to a particular
data array.


Clearly that is not true.

I would be grateful for an explanation of how a different image can
give rise to the same data array.


You've been given several.


All you have done is reiterate the claim. Can you give a step by step
explanation along the lines of the one I have just given?



Eric Stevens
  #57  
Old June 3rd 09, 10:43 AM posted to rec.photo.digital,uk.rec.photo.misc
Eric Stevens
external usenet poster
 
Posts: 13,611
Default Could you actually see photos made from RAW files?

On Tue, 02 Jun 2009 22:00:08 -0800, (Floyd L.
Davidson) wrote:

Chris H wrote:
In message , Floyd L. Davidson
writes
Everything is either one or the other and
nothing can be both.)


This is not correct. There are plenty of mixed devices about. Analog
Devices make a few of them.


You can have a complex device that has, for example, an
input that is one and an output that is another. But
you cannot have a signal that is both. "Everything"
means an atomic device, not a complex device. (My
apologies, I wrote the above expecting common sense
readers who understood the context.)

That is *not* part of the firmware. Firmware, other
than setting the ISO gain, has no part in any of that
other than turning it on and off.

You are referring to 'firmware' as though it was 'hardware'. Yet Nikon
can program the camera to behave differently so some software/firmware
must be involved.


Perfectly correct.


That does not cause hardware to become firmware.


Then what do you think firmware is? Its a mixture of hardware and
software.

I am referring to that as hardware because in fact it is
hardware. It is not done with software/firmware.


Yes it is. What is more I can supply the tools to write the firmware.


So you think the analog amplifiers and the ADC are
firmware and can be done with software tools??? That's
a bit of abject ignorance.


And that's a bit of dishonest argument, unless you insist on believing
that that the digitisation of the sensel charges is the entirety of
the process.

It's done with hardware.

(I can't tell you which but We have supplied software/firmware tools to
more than one OEM digital camera company (P&S variety)


Not for those functions you haven't.


But he never claimed it was just for those functions.



Eric Stevens
  #58  
Old June 3rd 09, 10:52 AM posted to rec.photo.digital,uk.rec.photo.misc
Eric Stevens
external usenet poster
 
Posts: 13,611
Default Could you actually see photos made from RAW files?

On Tue, 02 Jun 2009 23:17:16 -0800, (Floyd L.
Davidson) wrote:

Eric Stevens wrote:
On Wed, 03 Jun 2009 11:51:59 +1000, Bob Larter
wrote:

Eric Stevens wrote:
On Tue, 02 Jun 2009 02:09:19 -0800,
(Floyd L.
Davidson) wrote:
[...]
The definition of "analog" is that the signal (in this
case it would be the output signal from the sensor) is
continuously variable (it has an infinite number of
possible values). If it is "digital" then it must have
a finite set of discrete values. (Note that the two
definitions are together all inclusive and are mutually
exclusive. Everything is either one or the other and
nothing can be both.)

Haw. You are now claiming that it is possible to have a continuously
variable number of electrons. I maintain the number of electrons can
only be represented by integers.

By that exact same logic, resistors capacitors & transistors should be
called "digital" devices, but they aren't. The industry definition of
"digital" is something that only works with binary levels. Everything
else is called "analog".
References:
http://en.wikipedia.org/wiki/Digital_electronics


"In a digital circuit, a signal is represented in discrete states or
logic levels." - but they don't have to be binary.


What's your point? Binary is necessarily digital, but
digital is not necessarily binary (though any value that
is digital can necessarily be encoded in a binary form).
Got that?

The point is still that while the number electrons on
the head of a pin might be discrete, the current
produces by the flow of those electrons is *not*
discrete, and therefore is analog.


Its not a question of current. Its a question of the number of
electrons.

Of course the output of an electronic sensor in a camera
is the analog current, not the discrete number of
electons capture.


The output of a sensor is electron charges, which is quantized.

http://en.wikipedia.org/wiki/Analog_electronics


"Any change in the signal is meaningful, and each level of the signal
represents a different level of the phenomenon that it represents."


That is correct. Any change is meaningful on the
*input* to whereever the signal goes. It does *not*
necessarily mean it somehow is meaningful to anything
else (such as the number of electrons that cause the
signal to exist).


Who is trying to say it is meaningful to anything else?

This isn't the case with the output from a charge amplifier. 0.050,000
volts represents 50,000 electrons. 0.050,000,4 volts still represents
50,000 electrons. But 0.050,001 volts represents 50,001 electrons as
does 0.050,000,6 volts.


Is that supposed to make sense?


Yes, and it does.

The output from the amplifier is an analog signal.


So you keep saying. But if you can measure it with sufficient accuracy
and discard rounding errors (as can easily be done) you can read the
output as integer - which is digital.

Anything you thing means otherwise is nonsense. If you
doubt that, explain how and why it is fed to an analog
amplifier and then to a device called an
Analog-to-Digital-Converter.


It is the A to D converter which precisely measures the voltage to it
to be able to read as integer numbers. That's what I was trying to
explain to you above when you asked "Is that supposed to make sense?"


In summary:
---
Analogue electronics (or analog in American English) are those
electronic systems with a continuously variable signal. In contrast, in
digital electronics signals usually take only two different levels. The


That isn't really true, about "signals usually take only
two ...". In fact the entire digital Public Switched
Telephone Network (PSTN), as well as virtually all of
the music and video that is digitally recorded, uses
what is called an m-ary level encoding. In most cases
that is a 255 level PCM digital signal.


At least that's got you away from insisting that they always have to
be binary.

term "analogue" describes the proportional relationship between a signal
and a voltage or current that represented the signal.

" ... _usually_ take only two different levels." But what about Rambus
XDR memory which uses three different levels? Two levels are used
because they are the simplest.

In the case of an image sensor, the output voltage is an analog to the
light level that impinges upon it.


It still has to be capable of accurate digitisation and to that extent
it is digital.


That statement is pure nonsense. It doesn't "have to be
capable of accurate digitisation", whatever it is that
you think that means. It is not digital in any way
until it *is* digitized.


Electrons. Integer number of electrons. Nothing analog about integer
numbers.



Eric Stevens
  #59  
Old June 3rd 09, 11:16 AM posted to rec.photo.digital,uk.rec.photo.misc
Eric Stevens
external usenet poster
 
Posts: 13,611
Default Could you actually see photos made from RAW files?

On Tue, 02 Jun 2009 23:00:27 -0800, (Floyd L.
Davidson) wrote:

Eric Stevens wrote:
It can be OK for you to do that if you indicate that that is what you
have done. But you don't do that. You just delete blocks of text. This
can result in me appearing to say something other than what I actually
said. It can also result in the deletion of the explanation and
justification of what I did say.


It doesn't. What you said remains in the original post
for all to read. I quote just enough to refresh a
reader's memory on what it was. That has *always* been
the standard practice on Usenet, though in recent years
there have been many many fools who cannot understand
how to write concisely nor accurately. But your lack of
ability to do so is not a cause for me to take on the
same poor style that you use!

You can't claim that you don't know any better than this if only for
the twenty years of experience you have had with Usenet. What you have
been doing would not have been tolerated for one second twenty years
ago (yeah - I was there too).


Can I assume you didn't have a clue then either?

See
http://www.softdevlabs.com/personal/Usenet101.html

"Please remember that when you do snip portions of a person's
post, it's extremely important that you not only indicate that
you've done so, but also where you've done so. [5]

The commonly accepted way to indicate snips is to simply insert
the string "snip" (or similar notation) on a line by itself at
the spot where the deleted text used to be. "


You saw it on the Internet, so it must be true. Sheesh.
Cite an authoritative source. (Actually, I'll challenge you
to find anything at all from 20 years ago that says anything
like that.)


I mightn't find the rules but I can find plenty of examples where that
was what was done.

Okay, you don't know what an analog device is, so lets go
over that too.

The definition of "analog" is that the signal (in this
case it would be the output signal from the sensor) is
continuously variable (it has an infinite number of
possible values). If it is "digital" then it must have
a finite set of discrete values. (Note that the two
definitions are together all inclusive and are mutually
exclusive. Everything is either one or the other and
nothing can be both.)


Haw. You are now claiming that it is possible to have a continuously
variable number of electrons. I maintain the number of electrons can
only be represented by integers.


So what? That makes the number of electrons digital.


Can I quote that to the Floyd L. Davidson with whom I've just been
arguing?

But we aren't actually measuring the number of electrons,
are we? We are measuring the current that flows as a
result of the charge that was stored (which is roughly
proportional to the number of electrons). The current
that flows is affected not only by the number of
electrons, but how fast they move and which direction
they go. Both of those characteristics are continuously
variable.


Thats why the actual measurement is of charge 'q'.

And hence electric current is analog, and so is voltage.


And you are the guy who has just explained that 255 levels of current
or voltage can be used to carry tone signals. But no, that's not
digital or digitized. :-(

Now, you may notice that the output of the sensor is a
voltage which is continuously variable over an infinite
number of values between 0 and 1 volts. That makes it
an *analog* device by definition.


The output of the sensor is an electrical charge.


Actually it is a current flowing into the input
impedance of an amplifier, and thus producing a voltage.


That's how the electrical charge is measured.

The amplifier is affected by the voltage, which is an
analog parameter.


If you measure it with sufficient precision you can use it to carry
digital data.

The electrical
charge is dumped into a charge amplifier and it is this which outputs
the voltage. This is the first step in transforming sensor image into
the RAW data file.


And it is clearly an all analog process.

That analog data is fed into a device that converts it
to digital data.


The output of the charge amplifier is then digitised. This is the


Actually it is a voltage amplifier.


Ew've done that bit already.

second step in transforming sensor image into the RAW data file.


Well, actually it is then run through ISO amplifiers,
but we could ignore those is you like.

The output has a finite set of
discrete values. If, for example, it is a 12-bit
digital signal then there are as many as 4096 values.


In the case of the Nikon D300 the RAW file can be output as either 12
bit or 14 bit. It is likely that before it can be transformed into
either of those formats it is processed in the camera in some other
format.


Why is that likely? That is what the output of the ADC
is, and all that necessarily happens after that is the
data stream is read by the CPU so that it can be written
to the file.


But in what form is it whenit is read by the CPU - 12 bit or 14 bit or
something else again?

These values are not continuous (i.e., 3 and 4 are
discrete and there are no values between them as there
would be for an analog signal), hence they are discrete,
and the signal is by definition *digital*.


Before it hits the RAW file, the data is further massaged.


For several paragraphs now your comments have had
absolutely nothing to do with the text you are quoting.

What's your point?


I'm beginning to think you really don't know anything about the logic
of any of these processes.

The reason I've been stating that there are many
possible images which can produce the same digital data
set is because the analog signal to produce any single
one of those 4096 values has an infinite number of
possible values.


Not so.


Claim that all you like, but it is true.

The digital value of say 1612 corresponds with only one state
of the particular sensor element.


False. It corresponds to a range of values. Because
the range is analog, there are an infinite number of
possible values in that range.


Analog electronic charge. Haw!


After the data is digitized, it has one value (1612) and
you cannot determine which of the infinite number of
analog values that could be 1612 it actually was to
start with.


You might be correct if they truly were analog, but they aren't.

If you know the chain of
transformations between the sensels and the corresponding data of the
RAW file you can work it backwards to derive from the RAW file the
state of the individual sensels which gave rise to the data in the
first place.


False.


So you keep saying.

The reason I've said you cannot precisely restore the
original image on the sensor is because you do not know
exactly which of the infinite number of possible values
for each digital value should actually be used for the
analog image.


But you do if you understand the nature of the transformation.


No, if you understand the nature of the transform then
you realize that exactly the opposite is true. The
digital value of 1612 might, for example, represent a
range of voltages between .25 and .30 volts. When you
look at the digital value of 1612, you cannot determine
if it was .26675382, or .28778391. All you know that is
was between .25 and .30 volts.


I think the design of sensels has progressed since you helped invent
them. Their charge can be read with much greater precision than you
seem to think.


Basic information theory. (Ever heard of Claude E. Shannon??)


Of course I have. What exactly does he have to do with it?


Everything.

He more or less defined all of it with mathematics, and
analyzed what it meant. Because of his work it was
decided that the telecommunications industry would
benefit from moving to a digital network and abandon
the analog network. It was also clear that digital
imaging would be much much preferred to analog imaging.
That is why inventions which appeared to be useful for
digital photography were developed instead of ignored,
even though there was no market at all for them at the
time.


I know all that. But what does he have to do with this particular
argument?

I am referring to that as hardware because in fact it is
hardware. It is not done with software/firmware. This
is much like the way you insisted for article after
article that the RAW data had been interpolated...


You had led me onto the garden path for that one.


You are the one who takes these hikes into fantasy land
Eric, not me. We are discussing a topic that I've been
working with for literally decades, and one that I'm
familiar with down to the bit diddling level. I may not
always be able to describe things in a way that every
given individual can understand clearly, but with help
from the individual I can eventually find it. The
problem here is that while I clearly do understand all
of this extremely well and you don't, you won't help
with learning it.


It takes two to cooperate. Apart from that, I think we are approaching
this from two different directions. My background includes university
training in physics, electronics and mathematics. My terminology is
different from yours (e.g. transform) and so to is my approach to the
problem.

Nevertheless there
is software between the formation of the image on the sensor and the
writing of the data to the RAW file.


But that software is *not* image manipulation software.
All it necessarily does is encode the data so that it can
be written to a standard file format.


In the case of the D300 I do not think that is the case.

That is why/how various problems
(e.g. vertical stripes) can be cured by a firmware upgrade.


That sounds more like the image manipulation that is done
to the JPEG conversion, not to raw data.


I'm talking of raw data. Then Nikons apply a characterisation curve to
the senso data before it is recorded as RAW file data. There is much
more.

Regardless, it
would also be possible to introduce banding by dropping
data bits or whatever as the data is encoded for writing
to a file. That is *not* image manipulation software, and
correcting it with a firmware upgrade does not support
your arguments.

The original argument was over whether or not it was possible to work
back from the RAW data and arrive at more than one sensor image. I

A nonsense idea, but...


Its not at all nonsense, even if you think it is so.


Except for one little problem: you can't do it. (That, as I
and everyone except you seems to realize, makes it nonsense.)


I don't have the information but I am sure the process is reversible
(Subject to statistical error limitations).

See
http://www.clarkvision.com/imagedeta...mance.summary/
for a better indication of the number of electrons you can expect to
deal with: 50,000 or more.


The little guy standing there looking into the well and
counting those electrons might be digital, eh?


In his own way, he is.

But since what cameras do is discharge the device
through an impedance and amplify the voltage, we don't
have a digital count of electrons, we have an analog
signal indicating how much charge there was. Of course
it includes noise, so even if we did know the exact
analog voltage (which as has been show, we cannot), we
still wouldn't be able to determine how many electrons
were actually captured.


How do you think you get a digital display to X significant figures on
a digital volt meter? Thats the same way that the output of a charge
amplifier is digitised.

Unless you happen to know that digital guy there
counting them, and he doesn't run away because of your
tin foil hat. Or some other nonsense...

article. It isn't rocket science. But it *is*
something I've been dealing with for 40 years now...
and hence it is not at all surprising that I might
understand it rather well and can explain it in 15
different ways. But it does make all of your petty
insults a bit of a joke, Eric.


Congratulations! 40 years ago you were working in Bell Labs along with
Boyle and Smith! And I thought you were only a psychologist.


Well, I didn't ever work at Bell Labs, but in fact I did
work for AT&T. The telecommunications industry of
course has been vitally interested in exactly this
business of digital vs analog data roughly since the
1930's in this context.


Boyle and Smith were the inventors of electronic imaging 40 years ago.
If you were working with electronic imaging 40 years ago you _must_
have been working with Boyle and Smith.



Eric Stevens
  #60  
Old June 3rd 09, 11:29 AM posted to rec.photo.digital,uk.rec.photo.misc
Michael J Davis[_2_]
external usenet poster
 
Posts: 14
Default Could you actually see photos made from RAW files?

Bob Larter was inspired to say
Eric Stevens wrote:
On Mon, 01 Jun 2009 06:12:17 -0400, nospam
wrote:

In article , Eric
Stevens
wrote:

[..]
I've quoted
from the original articls, and you still keep trying to switch to
conversion from RAW to JPG. That's an entirely different question.
Then stop talking about processing the RAW data to make an image.
I haven't been. If anything I've been talking about working backwards
from the RAW data file to reconstruct the original image.
that doesn't make any sense.

I'm talking in the hypothetical sense of being able to derive from
the
RAW data the light pattern which fell on the sensor to create the RAW
data in the first place. In the case of RAW data which has not been
messed around in some way there is only the one sensor image which
will correspond.


That's incorrect. In a Bayer pattern image sensor, for example, fully
half of the sensels can't 'see' red or blue light. As a theoretical
example, imagine if you projected a series of images onto the sensor,
patterned such that the only difference was in the amounts of red/blue
light on the green-sensitive sensels, you would get a series of
identical RAW files. This is obviously a very contrived example, but it
demonstrates the possibility.


ISTM to be relevant to point out that even if no processing of the data
is required (it is, of course if only to label the format and cell
layout) - the distribution of colour sensors are different from a tft
screen and so the RAW 'image' cannot be viewed without interpretation.

I'll go back to sleep now...

Mike
--


"I never have taken a picture I've intended.
They're always better or worse."
Diane Arbus

 




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