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12:02 AM
and you might be thinking "hah, its just the street ligths that are yellow, my town is also yellow at night"
daytime is also yellow and blue :)
ah, about QE for nikons, its about comparable. I had jsut seen the D800 wooping 57%, but something like D5000 is also mid30s
I dont have any conception of the nikon line naming so I dont know what "translates" to xxxD,xxD,xD canon series.. its getting harder with canon too, when 60D is not continueing the xxD series but 7D is...
@MichaelNielsen There are other ways to improve S/N as well. Canon uses a bias offset, which allows them some freedoms Nikon does not have, which is probably where the slight increase in S/N at high ISo comes from.
@MichaelNielsen Also, the latest Canon sensors are around 50% as well.
The 1D X is 47%, the 5D III is 49%.
The D3s, D4, and D800 are the only ones that have higher than 50% Q.E., and the highest is 57%.
Nikon's best currently has less than a 10% Q.E. lead on Canon's best.
Which technically SHOULD allow them to achieve at least ISO 51200 natively, but there are some significant differences in how Sony Exmor works that seems to preclude that.
I believe the highest native ISO exmor can achieve is 12800.
It may be due to the way their on-die pipeline is split into analog and digital parts.
Most of Nikon's own sensors (the ones they manufacture(d), not Sony's) have worse Q.E. than Canon sensors.
12:21 AM
and then tehres the read noise numbers on the site. 50D has less than 40D while reviews went crazy over that 40D has less noise than 50D, complaining they put too many pixels per area with the 50D
there is read noise and photon noise
read noise may be less
as an intrinsic property of the sensor
photon noise, in the abscense of a sufficient increase in Q.E., is a property of pixel density
I thoguht read noise was so much higher than photon noise that photon noise was leglitiable in comparison
the 50D has smaller pixels, but only a 5% improvement in Q.E.
igher = more annoying
@MichaelNielsen hell no...photon noise is dominant except in the lowest signal ratios
12:22 AM
Photon noise exists at every brightness level
it is due to the random nature of light
It is why a blue sky tends to be noisy
yes I know the poisson dsitribution
the sky itself may be fairly bright, but it still tends to be noisy, even on the best sensor
read noise, on the other hand...
at it's worst it is 38.2e- (in the 1D X)
the 1D X saturation point is 90367e-
the maximum read noise level is a mere 0.0004% of the maximum signal
It also only matters at the lowest ISO settings.
and then only in the shadows
the noise is higher at higher brigthnes but you notice it less
the benefit of Sony Exmor is it's digital noise reduction in its CP-ADC logic
@MichaelNielsen photon noise, yes, read noise no
12:25 AM
unlike the read noise that you notice in the blacks even if the iamge is well exposed
it is all a matter of S/N
in the shadows, your signal may only be 100e-, maybe even 50e- for deep blacks
at that level, noise is a significant percentage of the signal
so it is more apparent
since exmor effectively has a 3 e- read noise level at all ISO settings, read noise is the same percentage of a low signal regardless
another thing, Canon uses a bias offset
where as Nikon/Sony do not
nikon and sony effectively clip blacks entirely above the noise floor
and it is not possible to register a signal below that clipping level
Canon, on the other hand, since it uses a bias offset, renders shadows or low exposures frequently unusable because signal and noise become mixed
and some of their read noise only exhibits as high as 25-35e- in certain areas (such as FPN and HVBN)
Ive been surpised at what my 40D can do today. I took iamges I thoguht Id need a fullframe to do, and all it took was a good lens and manual focus (well, manual everything).
so there can be usable image pixels in between horizontal and vertical bands
but because that signal is intruded upon by read noise, the whole thing is effectively unusable
Canon needs to rethink their sensor design, and find a way to either eliminate read noise (or at least reduce it to 3e- or less), or clip the black levels above the maximum level of read noise
ah so thats why. sometimes I jsut have to go b/w to make it usable if its underexposed
Ironically, that is how most sensor designs work.
Only Exmor is really significantly different
But Exmor is being used in more and more of Canon's competition, and they need to step up their game.
12:31 AM
even if it is nicely exposed than a person wearing a black jacket can be annoying
I have exmor in my ninja camera
Im not a fan
washed out details
sony wx1 :)
but it records concerts really well
maybe my lumia 920 can replace it
will wsee at next concert
oh, well
that is a BSI small form factor sensor
it is an Exmor, but the pixels are TINY
that is like comparing an elephant to a flamingo
Exmor and Exmor R are not really comparable
but still it seems to me that nikon vs canon, canon has more micro contrast underneath the noise, and nikons wash out some details, have you the same impression?
yeah, I do
regardless, images from a Nikon have far more usable shadows, washed out or not
Canon's deepest black levels (negative bias values) definitely seem to be more contrasty, with a slight red tint sometimes. Nikon's deepest black levels (down to zero, they do not have negative bias) appear to be blueish gray. I think it is the blueish gray tint that makes Nikon shadows appear a bit washed.
12:50 AM
well, in post we can clip teh blacks above the noise floor too, if we choose to. but we get teh choice. why should sony do it it for you , so you can never get the details back?
that is not quite what I mean
they clip all noise
there is always a certain amount of noise in a circuit
in an Exmor, the value that registers as 0 is actually not at purely zero electrons.
there are always some electrons in the circuit
Sony clips whatever the average of the amount of noise in the circuit is
so, if it is say around 30 on average
then they would set the zero level at 31
now, there are some fluctuations, so there will be a low level of read noise, and there are still FPN and HVBN noise sources
the rest is eliminated by their CP-ADC
Canon differs, in that they effectively use zero electrons as the minimum possible signal level, and set the base image signal readout level at some bias offset.
and if I udnerstood you correctly canon substracts divides the 30 by , say, 5 so teh 0-30 is scaled to 6 and clips at 0 so the signal details are intact, but added some noise?
Because of the bias offset, Canon's signal effectively ranges from some negative number (-512, -1024) up through the maximum signal, which is 2^14 minus the bias offset (1024, 2048, etc.)
Now, Canon can choose to clip blacks (set the black point) wherever they want in the bias offset, a range of 1024 or 2048 in most of their current cameras.
they could pick black to be -137
it could be -989
if it is -989, and read noise is 38.2
well, some noise will leak into the image signal
if they pick he full -1024, then there is the potential of 38 to 39 electrons worth of electronic noise in each pixel leaking into the image signal.
if sonys adc has NR , that should be the reason they sacrifice detail
Canon uses an analog CDS, but it is not nearly as effective as Exmor's CP-ADC and digital noise removal
1:01 AM
all filters filter signal details too
even teh advenced wavelets
Sony's CP-ADC uses the reset read to determine read signal, pattern noise, banding noise, and PRNU
it stores the "read noise level" of each pixel in CP-ADC at reset as a negative digital offset
so they both have ofset, one analogue and teh other digital
then, when it reads the actual image signal, which will have roughly the same amount of read noise for each pixel, the negative offset previously recorded effectively eliminates read noise in the image, and once positive digital units are read, they represent nearly pure image signal
well, bias offset is very much an analog and signal power thing
bias offset is not much like the kind of digital offset Exmor uses
Exmor's digital offsets are usually quite small for each pixel
a few units or so
Canon's bias offset can be quite large, and it is effectively dynamic and arbitrary
Canon's offset effectively allows useful signal and electronic circuit signal to mix in a bad way.
Exmor's offset is explicitly designed to identify and eliminate electronic circuit signal as precisely as possible, leaving behind the purest image signal they can.
so tehy a assuming that the read noise level is hte same teh usec later after the reset
which its not
as its not a smooth sine curve
that can be predicted
as far I remmber the read noise is uniform random generator
eh, photon noise is gaussian
read noise tends to have certain patterns
1:09 AM
so it can be (at eth range -100 to +100) -99 at teh reset when teh measure and +100 the next
there is some random element to it
the exact charge in the pixel at reset time can vary a little
and photon noise is poisson
but it is generally not significant
and the elctronic noise of guassian
poisson, gaussian, same basic thing
1:09 AM
gaussian is fixed std dev
possion has higher std dev at higher brightness
it is a probability curve
both are probability curves
the nasty kinds of read noise tend to be fixed
uniform noise is a p cruve too, its jsut constant :)
read noise comes in many varieties
there is no simple gaussian probability curve for "read noise"
has the "window box" shape
for reset current there might be
but reset current is only one type of noise
there is fixed pattern noise, which is a permanent attribute of a given sensor
1:11 AM
the box pdf is a pdf no less than the guassian pdf
there is banding noise, which tends to be a mix of fixed and semi-random noise
there is also a slight differential between the response of each transistor
are you taliogn about the fixed cmos pattern?
which might follow a gaussian distribution
there are thermal noise effects, which tend to occur in localized areas
and which also enhance the impact of FPN
where each pixel has its own unique gain slifhtly differnt form its next?
well, no
There are a couple patents for variable per-pixel gain
1:13 AM
not talking abotu that
but I don't believe any commercial sensor in a DSLR uses that yet
I mean response
not every pixel will respond the same way to stimulous
Im takning about that evern since cmos was invented, they had the trouble veruss ccd that the brightness of each pixel varied
nor will every transistor at each pixel behave exactly the same way
so they have to subtract a refrence frame
@MichaelNielsen CDS, Correlated Double Sampling
Canon uses an analog form, Exmor uses the digital approach I described
analog CDS tries to read out the reset current when the signal is read, similar to CP-ADC digital CDS
but it is not ideal...the reset charge can differ from the same charge when the exposure is read out
Canon has to deal with signal levels right down to zero electrons
Exmor, as I gather, has the benefit of most read noise simply being clipped, so the amount of reset signal to deal with in the first place is fairly low
and this has smaller variation
1:17 AM
but the raw converter can choose its own black level, above the noise (ie you as user) ie yo ucan clip it like xmor does
but you get the choice
no, heh
in Canon, useful image signal and read noise are mixed
useful image signal may only go to -350, where as teh bias offset allows as much as -1024. Read noise may reach right up to signal level 0 or higher.
In an Exmor
image signal starts where read noise is clipped
I don't know how they do it
maybe it is all done through their CP-ADC
but the patents and documents I've read only describe the digital CDS and the ability of each ADC to compensate for per-column banding
if we agre that they have lost details that explanation doesnt make sense,. if tehy can magically clip teh noise wihtout signal they wouldnt lose any.
but in all of the papers, the digital CDS reset signal tends to be only a few units
not thousands
maybe in actuality the reset signal is much greater
if so, then all noise removal is handled as digital units
but I'd expect them to have the same problems Canon does with a bias offset
and they do not
you are most certainly not losing anything with an Exmor
the simple fact of the matter is that Exmor retains two stops of increased shadow detail that, in a canon, is mixed with read noise
Canon uses analog CDS, has no FPN or HBVN removal
and they have problems with all three...dark current, FPN, and HVBN
Exmor has very slight problems with dark current noise, however it definitely seems to follow a more random distribution pattern and the maximum noise signal is rarely higher than 4e-
That means that you can recover useful image detail right down to nearly ZERO signal level.
I hope canon refrains from adding a filter you cant turn off
I dont believe in a filter that "knows" waht is noise and what isnt
It may be a bit washed out once you get down that far, but the simple fact of the matter is no canon sensor on earth allows you to make effective use of signal levels that low.
Canon blacks may be more contrasty, but they tend to be unusable because they have bright red banding noise and dark current noise all over the place...half the time you can't tell if it is noise or image detail your looking at when you get into the blacks.
So it doesn't matter that you can't "turn off the filter", which it isn't really a filter.
Exmor simply retains far more shadow detail than Canon's do, and the detail they retain is usable, without interference from banding or FPN until you get down to the bottom few levels of black (i.e. a pixel with RGB values 0,0,0; 1,1,1; and maybe 2,2,2)
If you want more contrast with an Exmor, tweak the tone curve, and your set.
1:27 AM
and yet, you still use canon?
Ergonomics, glass, yes.
But, I also tend to shoot at ISO above 800 95% of the time anyway.
So the benefit of Exmor is not applicable.
Exmor can only retain shadow detail that it can capture in the first placew.
You lose roughly a stop of dynamic range per stop of ISO.
At ISO 100 a 14-bit ADC will allow a bit less than 14 stops of DR.
ooh another strange thing about the graphs. canon has a expetected DR curve
nikon data goes upa nd down
At ISO 200, you get a bit less than 13 stops of DR. At ISO 400, you get a bit less than 12 stops, which is right in line with most Canon sensors...which sit between 11.5 and 12 stops of DR for ISO's 100-400. At ISO 800, you are limited to just less than 11 stops of DR, etc. etc.
I thoguht iso 200 was gain=1.0
Gain = 1.0 is called Unity Gain
it is very rare that you achieve unity gain at a selectable ISO setting
gain at ISO 100 is usually greater than 1
1:29 AM
ok.. I mean iso 200 = std gain
and iso 100 = attenuation
400 = boosting
so ideal DR = 200 iso
ISO 100 is base these days, for everyone
no, hell no
ISO 100 tends to give you the best DR, regardless of brand
I read many laces that 200 iso is hte best DR
ISO 100 is the highest gain
in the 1D X, gain is 6.7 e-/DU
at ISO 200, gain is half that
so 3.35e-/du
ISO 400 half again, so 1.675e-/du
ISO 800 is 0.8375e-/du
1:32 AM
higher iso = higher gain
eh, no
higher gain = less needed e / du
um, no
lets say we have a full well capacity of 100,000 electrons
your cd player has a certain fixed output and when you turn up teh amp (= higher gain) you trandfer that same signal to higher output, ie. less db per output db
and a maximum digital signal level of 2^14, or 16384
your maximum digital signal as numeric units at low ISO is LESS than your maximum analog signal as electrons
so, you MUST use multiple electrons per DU at low ISO
in our case, 100000/16384
1:34 AM
nt a signal that gives output 256 to give output 16000 so you need more gain
you want....
that would be 6.1e-/DU at ISO 100 for a 100,000 electron FWC
Now, ISO does not actually change the amount of light at the sensor...it can't. Changing ISO does only one thing: reduce the number of electrons that represent maximum analog signal.
So, at ISO 200, our maximum analog signal level is 50,000 electrons.
50000/16384 = 3.05e-/DU
in an image sensor, gain drops as ISO increases
thats my ppoint, the light on teh sensro is fixed like the output of the cd player
ergo you need more gain
because you are allocating fewer and fewer electrons per pixel, and effetively "wasting" more and more of the pixels full capacity
in indeustrial cameras gain is actually called gain
and is not in 1 stop increments
well, all I know, from reading a gazillion patents and technical papers and blogs
1:37 AM
and if you increase the gain you get the same effect as increasing teh iso on the photo camera
is that "gain" as it is used in a CIS device is the ratio of electrons to digital units
and on those cams teh default gain is higher than teh minimum gain
here, Roger Clark's (Ph.D. in this stuff) analysis of the 1D X: clarkvision.com/articles/evaluation-canon-1dx/index.html
and the data sheets have the formula from teh "parameter" values to actual DB
in the little table near the beginning, he has a column: Gain e/DN
1:38 AM
and guess what: minimum gain = -3db
= -1 stop
well, that doesn't seem to apply to commercial grade DSLR sensors
ISO 100 -> 100000/16384
ISO 200 -> 50000/16384
ISO 400 -> 25000/16384
ISO 800 -> 12500/16384
well, here on this site I read the reply about iso from one of the gurus near quote out of memory "actually iso 100 attanuate the singal by a stop effectively reducing DR, so you should be using 200 by default"
ISO 1600 -> 6250/16384
@MichaelNielsen That was Nikon manufactured sensors, and that was only the case over four years ago.
Since Nikon started using Exmor and sony tech in their own sensors, that is no longer the case.
Nikon has not used ISO 200 as base ISO for a long time.
Canon has always used ISO 100 as base ISO.
and on sensorgen the data for 40D is equal for iso 100 and 200 showing that something "is up": sensorgen.info/CanonEOS_40D.html
yeah, read noise is "up"
from sensorgen:
ISO 100: Read noise 19.6e-, sat 40311e-, 11.0 stops
ISO 200: Read noise 11.7e-, sat 24668, 11.0 stops
read noise dropped at ISO 200, but so did maximum saturation
the ratio remained the same
thus...11 stops
1:43 AM
ofc teh info could be outdated and at some point they changed the refernce iso to 100 , makign the "expanded ISO 50" be teh -3 db gain
Canon's CDS is over a decade old
Expanded ISO 50 doesn't change the power or gain
it is actually a shift in exposure and digital compensation
bit shift?
industrial cams have that
ISO 50 is basically ISO 100 with some behind the scenes exposure trickery and a digital exposure shift to compensate
you LOSE DR at ISO 50 because of that
but the power levels and gain at the sensor are exactly teh same as ISO 100
every current commercial (consumer, prosumer, or pro) DSLR on the market these days uses ISO 100 as base ISO
some have an Expanded 50, some have Expanded ISO's above their maximum native
from ISO 100 through the maximum native ISO, the number of electrons per digital unit drops by a factor of two for each stop of ISO increase
so, fewer and fewer electrons are used to generate single digital units
at some point you have a crossover, where one electron is converted into one digital unit
that is "unity gain"
unity gain is usually somewhere between ISO 200 and ISO 800
it might be closer to a third stop setting
it is rarely ever an exact selectable ISO setting
I guess technically speaking, the per-pixel amplifiers are still putting out voltage
rather than DU...digital units only come into play at the ADC
so, assuming per pixel amplifiers in a CMOS sensor convert input voltage to output voltage
g = log(Vout/Vin)^2
I figure the formula would be:
if input voltage is 100,000 and output voltage is 50,000, gain would be -0.6dB
at ISO 200
that bells
deci is 10*
and its amplitude not enerry
yeah...that is log base 10, not log base 2
1:52 AM
so its not power2
so its 3db
well, I don't know what the power input and output would be
pixels register charge
I'm sure there is a way to convert the voltage to power, but I don't have all the information to do so.
Im pretty sure I looked it up recently if its 6db per stop or 3db
and found it was 3db
well, wouldn't that depend on what the full well capacity was?
I mean, all sensors are 14-bit these days
I always get shaky about when it is 20-log vs 10*log
but not all have the same full well capacity in terms of charge
oh, I guess my formula above was wrong
it should be:
g = 10 log (Vout/Vin)^2
in 20 log:
g = 20 log (Vout/Vin)
that would mean 6dB
1:57 AM
you can convince me that 100 iso is refernce, but you will never get me to see iso 100 is "higher gain" than 200 :)
no, in terms of dB:
it is the power2 thaqt becomes 2* with log
ISO 100 = 0dB, ISO 200 = 6dB, ISO 400 = 12dB, ISO 800 = 18dB, etc.
if you compare voltages is it amplitudes
ie no power2
hmm, I just looked up gain: en.wikipedia.org/wiki/Gain
1:59 AM
if its P (watts) theres the power2 and it becomes 20*
Gain = 20 log (Vout/Vin) dB
Gain = 10 log (Vout/Vin)^2 dB
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