On Thu, 17 Jan 2019 18:54:51 -0500, nospam
wrote:
In article , Eric Stevens
wrote:
I wasn 't going answer this until I realised you had done some crude
editing of the article to which you were replying. In other words a
blatant lie.
their 'tests' claim what is physically not possible. that alone makes
them a scam
Example? - assuming of course that you are able to cite one.
of course i'm able. i do not make false claims. period.
--- Claim by nospam: ----
dxo measured 14.8 stops of dynamic range on the nikon d810 and d850,
which is *higher* than the theoretical maximum of 14 stops (14 bit a/d)
and in the real world, it won't actually get 14 stops.
that's not *my* claim.
it's basic sampling theory, something which you clearly do not
understand at all.
What is the frequency of the signal being sampled?
you're confused.
https://whatis.techtarget.com/defini...yquist-Theorem
"The Nyquist Theorem, also known as the sampling theorem, is a
principle that engineers follow in the digitization of analog
signals. For analog-to-digital conversion (ADC) to result in a
faithful reproduction of the signal, slices, called samples, of the
analog waveform must be taken frequently. The number of samples per
second is called the sampling rate or sampling frequency.
Any analog signal consists of components at various frequencies. The
simplest case is the sine wave, in which all the signal energy is
concentrated at one frequency. In practice, analog signals usually
have complex waveforms, with components at many frequencies. The
highest frequency component in an analog signal determines the
bandwidth of that signal. The higher the frequency, the greater the
bandwidth, if all other factors are held constant.
Suppose the highest frequency component, in hertz, for a given
analog signal is fmax. According to the Nyquist Theorem, the
sampling rate must be at least 2fmax, or twice the highest analog
frequency component. The sampling in an analog-to-digital converter
is actuated by a pulse generator (clock). If the sampling rate is
less than 2fmax, some of the highest frequency components in the
analog input signal will not be correctly represented in the
digitized output. When such a digital signal is converted back to
analog form by a digital-to-analog converter, false frequency
components appear that were not in the original analog signal. This
undesirable condition is a form of distortion called aliasing."
Now, bearing in mind that once the shutter has closed, a sensor site
sits there fat and happy (or thin and misrable) with as many photons
as the lens has thought to direct its way. No change. It's constant.
The frequency of the signal being sampled (i.e the number of photons
in the cell) is zero. According to Nyquist the sampling frequency must
be 2 x zero = zero. In other words it only needs to be sampled once.
Now what were you saying about sampling theory?
I challenged this comment which lead to an enormous thread which
fanned out in all directions. My contention was (and is) that the
number of bits that are used to code an image have nothing to do with
the dynamic range of the sensor. You can code it with as many bits as
you like with factors other than dynamic range determining the choice.
In particular there is no reason why a sensor should not have a
dynamic range wider than implied by the number of bits with which it's
output is encoded.
your contention is wrong, which you even admitted in the middle of the
thread.
I bet you can't cite the article where I did that.
i could if i was motivated to sift through more than 500 posts to find
it.
At one stage Ron C suggested I should explain my views with diagrams.
With some reluctance I have been getting round to doing this.
Preparing the diagrams so as to be able to deal with nospams of tghis
world is no mean task. In the course of my background research I found
the following thread from dpreview dated Mar 25, 2012.
https://www.dpreview.com/forums/thread/3170233
If you read that you will see that the maximum number of bits with
which it is worthwhile coding an image is determined by (a) read noise
and (b) pixel well size. DR vs number of bits is touched upon but no
one has suggested that sensor DR is limited by bit number.
the second post in that thread clearly does, further proof that you
don't understand the topic.
You mean where fvdbergh wrote "The dynamic range of a sensor is
typically limited by the signal to noise ratio (SNR), not the bit
depth of the analogue to digital converter (ADC)."?
nope.
i mean this pretty little pictu
https://3.img-dpreview.com/files/g/TS560x560~1835042.jpg
from this post, which is the second post in the thread:
https://www.dpreview.com/forums/post/41016086
Oh you persistent dummy! That's talking about the DR range coded into
the digital output signal by the ADC. It is not, never was, and never
will be the same as the DR of the analog input signal. (Maybe that's
too sweeping a statement but you get the drift).
it's even marked in evs, although that will no doubt cause you massive
confusion.
I have many times talked about scaling the sensor output to the ADC
and you have repeatedly told me I was wrong.
nope, what i told you is that the sensor output *could* be scaled, but
it isn't, therefore what you've said is not applicable.
OK. I will accept that. But I expect that's why you have snipped:
-------------------------------------------------------------
You mean where fvdbergh wrote "The dynamic range of a sensor is
typically limited by the signal to noise ratio (SNR), not the bit
depth of the analogue to digital converter (ADC)."?
Please note fvdbergh lower down wrote "A single point on the PTC will
give you the required SNR value, and hence the DR".
http://www.forzasilicon.com/2011/06/...-image-sensor/
or
http://tinyurl.com/y8ztqbhk will tell you that 'PTC' is 'Photon
Transfer Curve' and says of this " the sub-ranging technique, where
each segment’s conversion step size is scaled according to the photon
transfer curve (PTC) of a given pixel."
I have many times talked about scaling the sensor output to the ADC
and you have repeatedly told me I was wrong.
I think it it's safe to say you don't know as much of this subject as
you you think you do and you understand even less.
--------------------------------------------------------------
Please note "... each segment’s conversion step size is scaled
according to the photon transfer curve (PTC) of a given pixel."
Independent evidence that scaling can occor in the ADC process.
have you forgotten about your imaginary camera collection?
I think it it's safe to say you don't know as much of this subject as
you you think you do and you understand even less.
that would be a very unsafe comment.
it actually applies to you.
This hopefully is my last post on this subject.
hopefully, but i suspect not. either way, you haven't learned a thing.
--
Regards,
Eric Stevens