Paul Furman wrote: > Alan Browne wrote: >> Paul Furman wrote: >>> DRS wrote:
>>>> Why do Nikons seem to have a base ISO of 200? Is it a trade off of >>>> some kind?
>>> It allows a higher max ISO.
>> No relevance really.
> Is it just coincidence that low-ISO sensors on P&S start at lower ISOs? > I don't understand the details but the general principal seems to apply.
The lowest ISO should have no bearing on the max ISO.
With most sensors, gain (higher ISO numbers) is simply analog gain (pre-conversion) for the first few stops (from say 100 - 800 or 1600) and afterwards it is is digital gain. (Although recent higher ISO cameras from Canon and Nikon may have more analog gain before relying on digital). So there is no limit imposed by the lowest sensitivity.
Peter wrote: > Floyd L. Davidson wrote >> Peter wrote: >>> John Sheehy wrote >>>> DRS wrote
>>>>> Why do Nikons seem to have a base ISO of 200? Is it a trade off of >>>>> some kind?
>>>> The D3 uses a low silicon fill factor, and makes up for it with large >>>> microlenses, which, of course, fill the wells faster. <snip>
>> <big snip>
>> Read noise has, like shot noise, a Gaussian distribution >> so it is essentially random, and will mostly be seen in >> the shadows. To continue the analogy used above, it >> looks very much like a paper covered with mixture of >> black pepper and grey pepper.
>> Below a certain amount of exposure, the SNR of an image >> is very likely to be determined by read noise instead of >> shot noise. (Generally that is not a good thing.) >> Because read noise will be seen in the shadows it is >> generally more annoying to the human eye.
> Thanks for that explanation.
Yes, thanks Floyd. And JPS!
> My interest as a photo artist is simply to > make a nice picture. When Nikon says I can shoot at a higher ISO with > less noise, I am skeptical. I have a friend who claims he shoot a D300 > at ISO 1,600 without little perceptible noise. Yet I have not found that > to be the case on my D300.
This may be the usefulness of understanding this stuff. How do you get the best performance from whatever camera you have? ETTR (Expose To The Right) is one example of how to apply this knowledge, another is helping to decide whether to buy the latest mumbo jumbo technology and what it's worth for your particular needs.
D300 can produce very acceptable photos even at ISO 3200 when and if the light is almost daylight as color temp (over 4000 K) with a even smooth spectrum. For ex the interior of a house illuminated from windows, when the reflective surfaces are mostly neutral. No matter how low is this light. As long as the light is of "full spectrum" even very dim, the picture will have not suffer to much from noise. A second parameter is the dynamic range of the light in the photo. If the darkest area in the photo is not darker than 5-7 EV, then this is a factor to not develop the noise in an inconvenient way. So, even luminance and good spectrum are the factors that can produce pictures with less ugly noise. The remaining noise is more even luminance noise (less or no ugly chrominance), more like a powder, as film grain, that sometimes can add to beautiful bokeh, if exists.
From the other hand a bad light source, as the green or orange mercury street lights with the terrible spectrum, or the dim tungsten lights with yellow or brown lampshade that produce light of very low temp, often less than 2000K can push the cameras WB adjustment out of the limits even at ISO 200.
For ex if the light has a temp of 1800K (not rare), the blue channel is almost absent. In that case if we (or the camera) try to correct the color, not 100%, but even a little just to look more natural and full, we will amplify the blue channel even by more than 5 EV,. That means that even if we shot at 200 ISO, the blue channel will be amplified to even higher than ISO 6400 and then the noise will be terrible.
So under circumstances, we can have almost perfect photos at ISO 3200 and under other very noisy under ISO 800 (or less). Bad light quality and wide luminance range of the subject are the enemies of the low noise photo
Alan Browne wrote: > Paul Furman wrote: >> Alan Browne wrote: >>> Paul Furman wrote: >>>> DRS wrote:
>>>>> Why do Nikons seem to have a base ISO of 200? Is it a trade off of >>>>> some kind?
>>>> It allows a higher max ISO.
>>> No relevance really.
>> Is it just coincidence that low-ISO sensors on P&S start at lower >> ISOs? I don't understand the details but the general principal seems >> to apply.
> The lowest ISO should have no bearing on the max ISO.
Sure it should.
> With most sensors, gain (higher ISO numbers) is simply analog gain
Analog gain is lossy. When you amp up the signal from the image sensor, you also amp up the noise.
-- W . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^---------------------------------------------------------------
>>> Why do Nikons seem to have a base ISO of 200? Is it a trade off of some >>> kind?
>> The D3 uses a low silicon fill factor, and makes up for it with large >> microlenses, which, of course, fill the wells faster. In order to >> meter at >> ISO 100, the camera would have very little RAW highlight headroom, so >> ISOs >> under 200 are only offered as special modes. Apparently, they use the >> low >> fill factor to get more noiseless electronics at the photosites. This >> keeps read noise down a bit, but increases shot noise a little, too.
> Would you please explain this concept in English? I know about SNR and > why I get more noise at a higher ISO, but I don't understand the > difference between read noise and shot noise.
Read noise is related to the gain in the sensor amp, while shot noise is relatively constant in relation to the original signal.
-- W . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^---------------------------------------------------------------
>>>> Why do Nikons seem to have a base ISO of 200? Is it a trade off of some >>>> kind? >>> The D3 uses a low silicon fill factor, and makes up for it with large >>> microlenses, which, of course, fill the wells faster. >>> In order to meter at >>> ISO 100, the camera would have very little RAW highlight headroom, so ISOs >>> under 200 are only offered as special modes. Apparently, they use the low >>> fill factor to get more noiseless electronics at the photosites. This >>> keeps read noise down a bit, but increases shot noise a little, too.
>> Would you please explain this concept in English? I know about SNR and why I >> get more noise at a higher ISO, but I don't understand the difference >> between read noise and shot noise.
> "Photon shot noise", or "photon noise", or "Poisson > noise" or "shot noise" are all references to the fact > that light doesn't hit the sensor at a constant steady > rate. The rate variation results in noise because the > actual exposure is for some specified interval. Two > adjacent pixel locations may be illuminated exactly the > same, but in the particular interval that light was > allowed to fall on them it is very likely that one pixel > will get more light (light for that pixel was arriving > at a faster rate than for the other). The difference > between the signal from those two pixels is shot noise.
> Shot noise looks like a paper covered with a mix of salt > and pepper! It is also greater for more exposure (the > variation in rate increases as the amount of light > increases). Hence the place it is usually seen in > images is in the sky, or clouds, or other featureless > highlights. (So maybe we should say it looks like a > paper covered with a mixture of white salt and light > grey pepper.)
> Above a certain amount of exposure, the SNR of an image > is very likely to be determined by photon noise, in > which case it is called "photon noise limited".
> Read noise is all noise that is in the image as a result > of reading the data from the sensor (even if the lens > cap is on and absolutely no light has hit the sensor and > therefore the signal is 0). The base level of analog > voltage fluctuation on the sensor adds to it. Things > such as clock frequency variations in the ADC add to it. > In most discussions quantization distortion is included > in the "read noise".
> Read noise has, like shot noise, a Gaussian distribution > so it is essentially random, and will mostly be seen in > the shadows. To continue the analogy used above, it > looks very much like a paper covered with mixture of > black pepper and grey pepper.
> Below a certain amount of exposure, the SNR of an image > is very likely to be determined by read noise instead of > shot noise. (Generally that is not a good thing.) > Because read noise will be seen in the shadows it is > generally more annoying to the human eye.
Nicely put, Floyd.
-- W . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^---------------------------------------------------------------
On Wed, 14 Oct 2009 21:42:50 -0700, John McWilliams <jp...@comcast.net> wrote: : Paul Furman wrote:
: > John McWilliams wrote: : >> D. Peter Maus wrote: : >>> On 10/14/09 16:37 , Savageduck wrote: : >>>> On 2009-10-14 14:07:08 -0700, "D. Peter Maus" : >>>> <DPeterM...@worldnet.att.net> said: : >> : >>>>> LOL! Yeah, I still shoot my D70 daily. If you like D300 see if you can : >>>>> get your hands on a D700 for a weekend. : >>>> : >>>> The D700 thing is something I have been thinking of for a while now. : >>>>> : >>>>> You'll never need another woman. : >>>> : >>>> Well I have been on my own for almost two years now, and even though I : >>>> have the social life of a stump, a little feminine companionship : >>>> wouldn't be too bad from time to time. : >>>> : >>>> There is nothing more disturbing than a 60 year old in hormonal : >>>> distress. :-) : >>>> : >>> I'm right behind you at 58. : >> : >> I'm 'ahead' of you both at 65, but fortunately on weekends I enjoy the : >> company of a woman who likes what I do with : >> my equipment, and enjoys post processing almost as much as I do. We : >> both try to get it right in camera, and ususally do on the first shot. : >> Post processing is usually not strictly needed, but always seems to : >> make an image better with a bit of tweaking. : > : > I thought ladies liked 'pre-processing'. : > But wtf do I know at 45 & single again for the last 5 years :-( : : It's true that before the shot actually happens, good preparation leads : to superior results over a hastily composed frame or frantic release of : the shutter. : : And it's a poor workman who blames his tools, but a number of P+S'ers : claim they get satisfying results from their small units.
On Fri, 16 Oct 2009 10:21:42 -0400, "Peter" <peter...@nospamoptonline.net> wrote: : "D. Peter Maus" <DPeterM...@worldnet.att.net> wrote in message : news:hb5gjs$f9s$1@news.eternal-september.org... : > On 10/14/09 16:37 , Savageduck wrote: : >> On 2009-10-14 14:07:08 -0700, "D. Peter Maus" : >> <DPeterM...@worldnet.att.net> said: : >> : >>> On 10/14/09 15:53 , Savageduck wrote: : >>>> On 2009-10-14 11:04:56 -0700, "D. Peter Maus" : >>>> <DPeterM...@worldnet.att.net> said: : >>>> : >>>>> On 10/14/09 12:56 , Savageduck wrote: : >>>>>> On 2009-10-14 10:45:43 -0700, Alan Browne : >>>>>> <alan.bro...@FreelunchVideotron.ca> said: : >>>>>> : >>>>>>> Read all the gory details of this new body: : >>>>>>> : >>>>>>> http://www.dpreview.com/news/0910/09101402nikonD3s.asp : >>>>>> : >>>>>> Interesting. : >>>>>> It seems to me the real benefit is going to be in high ISO : >>>>>> performance : >>>>>> and the addition of sensor cleaning. I am not drawn to the video in : >>>>>> DSLR : >>>>>> trend. : >>>>>> Not being a pro or independantly wealthy I guess I am going to stick : >>>>>> with my D300 for now. : >>>>>> : >>>>> : >>>>> : >>>>> That D300 is no slouch, either. : >>>> : >>>> I'm happy with it, and I still have my D70 lifeboat. : >>> : >>> : >>> LOL! Yeah, I still shoot my D70 daily. If you like D300 see if you can : >>> get your hands on a D700 for a weekend. : >> : >> The D700 thing is something I have been thinking of for a while now. : >>> : >>> You'll never need another woman. : >> : >> Well I have been on my own for almost two years now, and even though I : >> have the social life of a stump, a little feminine companionship : >> wouldn't be too bad from time to time. : >> : >> There is nothing more disturbing than a 60 year old in hormonal : >> distress. :-) : >> : >> : > : > I'm right behind you at 58. : : : At 72 I'm ahead of both. Lots of fun years left, hopefully for all of us.
I've always assumed I was one of the oldest in the group, but I won't be 72 until next week!
: Differences: : Although I have a D300, with my 200 as a backup, I am seriously thinking of : a D5000 because the articulated LCD should give my back more mileage.
>>>> Why do Nikons seem to have a base ISO of 200? Is it a trade off of some >>>> kind?
>>> The D3 uses a low silicon fill factor, and makes up for it with large >>> microlenses, which, of course, fill the wells faster. >>> In order to meter at >>> ISO 100, the camera would have very little RAW >>> highlight headroom, so ISOs >>> under 200 are only offered as special modes. >>> Apparently, they use the low >>> fill factor to get more noiseless electronics at the photosites. This >>> keeps read noise down a bit, but increases shot noise a little, too.
>> Would you please explain this concept in English? I >> know about SNR and why I get more noise at a higher >> ISO, but I don't understand the difference between >> read noise and shot noise.
>Read noise is related to the gain in the sensor amp, while shot noise is >relatively constant in relation to the original signal.
Not true. Shot noise at the input to the sensor amp will be amplified just as much as read noise generated by the sensor.
There is a higher percentage of photon noise (shot noise) in higher brightness signals. There is a higher percentage of read noise at lower brightness levels.
Generally that means lower ISO images will more likely be photon noise limited and higher ISO images are more likely to be read noise limited. The later is generally detrimental because noise in the lower brightness areas is more annoying than noise in the higher brightness areas.
On Sat, 17 Oct 2009 08:21:46 +0300, "Dimitris M" <som...@yahooo.com> wrote:
: D300 can produce very acceptable photos even at ISO 3200 when and if the : light is almost daylight as color temp (over 4000 K) with a even smooth : spectrum. For ex the interior of a house illuminated from windows, when the : reflective surfaces are mostly neutral. No matter how low is this light. As : long as the light is of "full spectrum" even very dim, the picture will have : not suffer to much from noise. A second parameter is the dynamic range of : the light in the photo. If the darkest area in the photo is not darker than : 5-7 EV, then this is a factor to not develop the noise in an inconvenient : way. So, even luminance and good spectrum are the factors that can produce : pictures with less ugly noise. The remaining noise is more even luminance : noise (less or no ugly chrominance), more like a powder, as film grain, that : sometimes can add to beautiful bokeh, if exists. : : From the other hand a bad light source, as the green or orange mercury : street lights with the terrible spectrum, or the dim tungsten lights with : yellow or brown lampshade that produce light of very low temp, often less : than 2000K can push the cameras WB adjustment out of the limits even at ISO : 200. : : For ex if the light has a temp of 1800K (not rare), the blue channel is : almost absent. In that case if we (or the camera) try to correct the color, : not 100%, but even a little just to look more natural and full, we will : amplify the blue channel even by more than 5 EV,. That means that even if we : shot at 200 ISO, the blue channel will be amplified to even higher than ISO : 6400 and then the noise will be terrible. : : So under circumstances, we can have almost perfect photos at ISO 3200 and : under other very noisy under ISO 800 (or less). Bad light quality and wide : luminance range of the subject are the enemies of the low noise photo
My 50D gives excellent results at ISO 1000 in a room illuminated by a mixture of reflected sunlight and incandescent light. I did a shoot in such a room earlier this week, and my existing light shots at ISO 1000 needed less correction than those I did at ISO 800 with fill flash. I guess this is consistent with Dimitris's explanation. The reflected sunlight, which is very blue, must do a good job of filling the deficit in the blue channel left by the incandescent light.
> On Fri, 16 Oct 2009 10:21:42 -0400, "Peter"<peter...@nospamoptonline.net> > wrote: > : "D. Peter Maus"<DPeterM...@worldnet.att.net> wrote in message > : news:hb5gjs$f9s$1@news.eternal-september.org... > :> On 10/14/09 16:37 , Savageduck wrote: > :>> On 2009-10-14 14:07:08 -0700, "D. Peter Maus" > :>> <DPeterM...@worldnet.att.net> said: > :>> > :>>> On 10/14/09 15:53 , Savageduck wrote: > :>>>> On 2009-10-14 11:04:56 -0700, "D. Peter Maus" > :>>>> <DPeterM...@worldnet.att.net> said: > :>>>> > :>>>>> On 10/14/09 12:56 , Savageduck wrote: > :>>>>>> On 2009-10-14 10:45:43 -0700, Alan Browne > :>>>>>> <alan.bro...@FreelunchVideotron.ca> said: > :>>>>>> > :>>>>>>> Read all the gory details of this new body: > :>>>>>>> > :>>>>>>> http://www.dpreview.com/news/0910/09101402nikonD3s.asp > :>>>>>> > :>>>>>> Interesting. > :>>>>>> It seems to me the real benefit is going to be in high ISO > :>>>>>> performance > :>>>>>> and the addition of sensor cleaning. I am not drawn to the video in > :>>>>>> DSLR > :>>>>>> trend. > :>>>>>> Not being a pro or independantly wealthy I guess I am going to stick > :>>>>>> with my D300 for now. > :>>>>>> > :>>>>> > :>>>>> > :>>>>> That D300 is no slouch, either. > :>>>> > :>>>> I'm happy with it, and I still have my D70 lifeboat. > :>>> > :>>> > :>>> LOL! Yeah, I still shoot my D70 daily. If you like D300 see if you can > :>>> get your hands on a D700 for a weekend. > :>> > :>> The D700 thing is something I have been thinking of for a while now. > :>>> > :>>> You'll never need another woman. > :>> > :>> Well I have been on my own for almost two years now, and even though I > :>> have the social life of a stump, a little feminine companionship > :>> wouldn't be too bad from time to time. > :>> > :>> There is nothing more disturbing than a 60 year old in hormonal > :>> distress. :-) > :>> > :>> > :> > :> I'm right behind you at 58. > : > : > : At 72 I'm ahead of both. Lots of fun years left, hopefully for all of us.
> I've always assumed I was one of the oldest in the group, but I won't be 72 > until next week!
> : Differences: > : Although I have a D300, with my 200 as a backup, I am seriously thinking of > : a D5000 because the articulated LCD should give my back more mileage.
> Am I the only Canon user in this elderly crowd?
> Bob
Cease the profanity, before I rise up and smite thee with my cane.
Robert Coe wrote: > On Fri, 16 Oct 2009 10:21:42 -0400, "Peter" <peter...@nospamoptonline.net> > wrote: > : "D. Peter Maus" <DPeterM...@worldnet.att.net> wrote in message > : news:hb5gjs$f9s$1@news.eternal-september.org... > : > On 10/14/09 16:37 , Savageduck wrote: > : >> On 2009-10-14 14:07:08 -0700, "D. Peter Maus" > : >> <DPeterM...@worldnet.att.net> said: > : >> > : >>> On 10/14/09 15:53 , Savageduck wrote: > : >>>> On 2009-10-14 11:04:56 -0700, "D. Peter Maus" > : >>>> <DPeterM...@worldnet.att.net> said: > : >>>> > : >>>>> On 10/14/09 12:56 , Savageduck wrote: > : >>>>>> On 2009-10-14 10:45:43 -0700, Alan Browne > : >>>>>> <alan.bro...@FreelunchVideotron.ca> said: > : >>>>>> > : >>>>>>> Read all the gory details of this new body: > : >>>>>>> > : >>>>>>> http://www.dpreview.com/news/0910/09101402nikonD3s.asp > : >>>>>> > : >>>>>> Interesting. > : >>>>>> It seems to me the real benefit is going to be in high ISO > : >>>>>> performance > : >>>>>> and the addition of sensor cleaning. I am not drawn to the video in > : >>>>>> DSLR > : >>>>>> trend. > : >>>>>> Not being a pro or independantly wealthy I guess I am going to stick > : >>>>>> with my D300 for now. > : >>>>>> > : >>>>> > : >>>>> > : >>>>> That D300 is no slouch, either. > : >>>> > : >>>> I'm happy with it, and I still have my D70 lifeboat. > : >>> > : >>> > : >>> LOL! Yeah, I still shoot my D70 daily. If you like D300 see if you can > : >>> get your hands on a D700 for a weekend. > : >> > : >> The D700 thing is something I have been thinking of for a while now. > : >>> > : >>> You'll never need another woman. > : >> > : >> Well I have been on my own for almost two years now, and even though I > : >> have the social life of a stump, a little feminine companionship > : >> wouldn't be too bad from time to time. > : >> > : >> There is nothing more disturbing than a 60 year old in hormonal > : >> distress. :-) > : >> > : >> > : > > : > I'm right behind you at 58. > : > : > : At 72 I'm ahead of both. Lots of fun years left, hopefully for all of us.
> I've always assumed I was one of the oldest in the group, but I won't be 72 > until next week!
> : Differences: > : Although I have a D300, with my 200 as a backup, I am seriously thinking of > : a D5000 because the articulated LCD should give my back more mileage.
> Am I the only Canon user in this elderly crowd?
Hardly! Most* Canon users are secure enough in their prowess as photographers that they don't need to talk about their equipment all the time.... it takes only a handful to make it seem like the whole world......
> On Fri, 16 Oct 2009 10:21:42 -0400, "Peter" <peter...@nospamoptonline.net> > wrote: > : "D. Peter Maus" <DPeterM...@worldnet.att.net> wrote in message > : news:hb5gjs$f9s$1@news.eternal-september.org... > : > On 10/14/09 16:37 , Savageduck wrote: > : >> On 2009-10-14 14:07:08 -0700, "D. Peter Maus" > : >> <DPeterM...@worldnet.att.net> said: > : >> > : >>> On 10/14/09 15:53 , Savageduck wrote: > : >>>> On 2009-10-14 11:04:56 -0700, "D. Peter Maus" > : >>>> <DPeterM...@worldnet.att.net> said: > : >>>> > : >>>>> On 10/14/09 12:56 , Savageduck wrote: > : >>>>>> On 2009-10-14 10:45:43 -0700, Alan Browne > : >>>>>> <alan.bro...@FreelunchVideotron.ca> said: > : >>>>>> > : >>>>>>> Read all the gory details of this new body: > : >>>>>>> > : >>>>>>> http://www.dpreview.com/news/0910/09101402nikonD3s.asp > : >>>>>> > : >>>>>> Interesting. > : >>>>>> It seems to me the real benefit is going to be in high ISO > : >>>>>> performance > : >>>>>> and the addition of sensor cleaning. I am not drawn to the video in > : >>>>>> DSLR > : >>>>>> trend. > : >>>>>> Not being a pro or independantly wealthy I guess I am going to stick > : >>>>>> with my D300 for now. > : >>>>>> > : >>>>> > : >>>>> > : >>>>> That D300 is no slouch, either. > : >>>> > : >>>> I'm happy with it, and I still have my D70 lifeboat. > : >>> > : >>> > : >>> LOL! Yeah, I still shoot my D70 daily. If you like D300 see if you can > : >>> get your hands on a D700 for a weekend. > : >> > : >> The D700 thing is something I have been thinking of for a while now. > : >>> > : >>> You'll never need another woman. > : >> > : >> Well I have been on my own for almost two years now, and even though I > : >> have the social life of a stump, a little feminine companionship > : >> wouldn't be too bad from time to time. > : >> > : >> There is nothing more disturbing than a 60 year old in hormonal > : >> distress. :-) > : >> > : >> > : > > : > I'm right behind you at 58. > : > : > : At 72 I'm ahead of both. Lots of fun years left, hopefully for all of us.
> I've always assumed I was one of the oldest in the group, but I won't be 72 > until next week!
> : Differences: > : Although I have a D300, with my 200 as a backup, I am seriously thinking of > : a D5000 because the articulated LCD should give my back more mileage.
> On Fri, 16 Oct 2009 10:21:42 -0400, "Peter" <peter...@nospamoptonline.net> > wrote:
> : Differences: > : Although I have a D300, with my 200 as a backup, I am seriously thinking > of > : a D5000 because the articulated LCD should give my back more mileage.
> Am I the only Canon user in this elderly crowd?
Maybe there's more than one reason not to shoot flies with a Canon <duck>
> Peter wrote: >> Floyd L. Davidson wrote >>> Peter wrote: >>>> John Sheehy wrote >>>>> DRS wrote >>>>>> Why do Nikons seem to have a base ISO of 200? Is it a trade off of >>>>>> some kind?
>>>>> The D3 uses a low silicon fill factor, and makes up for it with large >>>>> microlenses, which, of course, fill the wells faster. <snip>
>>> <big snip>
>>> Read noise has, like shot noise, a Gaussian distribution >>> so it is essentially random, and will mostly be seen in >>> the shadows. To continue the analogy used above, it >>> looks very much like a paper covered with mixture of >>> black pepper and grey pepper.
>>> Below a certain amount of exposure, the SNR of an image >>> is very likely to be determined by read noise instead of >>> shot noise. (Generally that is not a good thing.) >>> Because read noise will be seen in the shadows it is >>> generally more annoying to the human eye.
>> Thanks for that explanation.
> Yes, thanks Floyd. And JPS!
>> My interest as a photo artist is simply to make a nice picture. When >> Nikon says I can shoot at a higher ISO with less noise, I am skeptical. I >> have a friend who claims he shoot a D300 at ISO 1,600 without little >> perceptible noise. Yet I have not found that to be the case on my D300.
> This may be the usefulness of understanding this stuff. How do you get the > best performance from whatever camera you have? ETTR (Expose To The Right) > is one example of how to apply this knowledge, another is helping to > decide whether to buy the latest mumbo jumbo technology and what it's > worth for your particular needs.
> Good stuff.
Yes indeed, it is good information. I now understand why many of my night harness racing images shot, at 3,200 and 1,600 were so noisy as to be almost unusable.
> Would you please explain this concept in English? I know about SNR and > why I get more noise at a higher ISO, but I don't understand the > difference between read noise and shot noise.
Sorry, I forget that I post in usenet sometimes.
I don't have time to read the other responses right now, so I don't know what is covered and what I agree or disagree with, but I'll just give a summary.
Shot noise is the only truly *necessary* noise in digital imaging. It is noise that is always in light because light itself is counted in whole particles. So, if you have a theoretically smooth, flat subject, you will never collect the same number of photons in all the pixels.
Read noise is noise generated by the camera, reading the sensor and digitizing the results. It only exists in current technology, and may not exist in future ones, if ways are found to digitally count photon strikes.
There are few main differences between read noise and shot noise:
1) Shot noise in an image is the same, as long as the absolute exposure is the same. IOW, if you take a shot of the same scene and lighting at ISO 1600 with f/8 and 1/100, you have the same shot noise if you had the camera set to ISO 100 and f/8 & 1/100. Read noise, with some cameras, especially CMOS DSLRs, changes when you change the ISO. With such cameras, there is almost no difference in read noise, relative to normal exposure, between the first 3 stops of ISO from base, and then well above that, they tend to have read noise proportional to ISO. Looking at it relative to absolute signal, read noise on such cameras is greatest at the lowest ISOs, and lowest at the higher ISOs.
2) In any given camera, at any given ISO, shot noise, relative to signal, doubles as you quarter the signal (2 stops less exposure), while read noise quadruples. So, the deeper you go into the shadows, the faster read noise increases compared to shot noise. Running out of photons is the least of your problems, when you decrease exposure, as read noise takes a greater toll than shot noise.
3) Shot noise and read noise have completely different relationships to real, detailed signal. Say you had a black-and-white checkerboard as a subject. As you decrease exposure, it gets to the point where the white checks don't look much different than the black checks, because they are faint, compared to the read noise "floor", which blankets over both check colors. They barely show through. If there were no read noise, and only shot noise, the black would be totally black, and the white checks would simply have a more speckled texture.
4) Only read noise has patterns in it. All those streaks and bands you see in images come from read noise - sloppy electronics without correction (most line patterns are correctable; manufacturers that have them are just apathetic about quality). Shot noise is kind of nice looking; like the actual texture of the image, especially at high pixel densities.
John Sheehy wrote: > Read noise is noise generated by the camera, reading the sensor and > digitizing the results. It only exists in current technology, and may > not exist in future ones, if ways are found to digitally count photon > strikes.
Such methods exist. I have devices using them. They work well. They have existed and worked well since, in some cases, the late 1940s. Solid state ones have existed for years. The problem is that they generate a bit too much heat: without active cooling am imaging device would overheat and the thermal electrons would ruin the noise performance, not to mention the device.
> Read noise is related to the gain in the sensor amp,
If you break the read noise down into two components, pre-gain and post- gain, the pre-gain part is the same and fixed for any absolute exposure, regardless of gain. For the post-gain part, the lower the gain, the more read noise there can be, relative to absolute signal.
There is no general history of higher gains causing more absolute read noise! I do have one camera that seems to be the exception; my Panasonic FZ50. It has the lowest absolute read noise at ISO 200, and the highest at 800 (but not a huge difference).
> Bob Larter <bobbylar...@gmail.com> wrote: >>Read noise is related to the gain in the sensor amp, while shot noise >>is relatively constant in relation to the original signal.
> Not true. Shot noise at the input to the sensor amp > will be amplified just as much as read noise generated > by the sensor.
"In relation to the original signal"?
> There is a higher percentage of photon noise (shot > noise) in higher brightness signals.
As a percentage of total noise. As a percentage of signal, shot noise is lowest with stronger signals. In *absolute deviation*, shot noise is highest with higher signals.
>> Read noise is related to the gain in the sensor amp,
> If you break the read noise down into two components, pre-gain and post- > gain, the pre-gain part is the same and fixed for any absolute exposure, > regardless of gain.
Yes, that's what I was trying to say.
> For the post-gain part, the lower the gain, the more > read noise there can be, relative to absolute signal.
Um, read noise is multiplied by gain.
-- W . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^---------------------------------------------------------------
Bob Larter <bobbylar...@gmail.com> wrote: >John Sheehy wrote: >> Bob Larter <bobbylar...@gmail.com> wrote in >> news:4ad9c4db$1@dnews.tpgi.com.au: >>> Read noise is related to the gain in the sensor amp, >> If you break the read noise down into two components, >> pre-gain and post- >> gain, the pre-gain part is the same and fixed for any >> absolute exposure, regardless of gain.
>Yes, that's what I was trying to say.
Fixed in terms of SNR. Not fixed in terms of output levels, and hence not fixed in terms of ISO settings.
>> For the post-gain part, the lower the gain, the more >> read noise there can be, relative to absolute signal.
>Um, read noise is multiplied by gain.
Not necessarily. He's talking about making a distinction between noise that is and noise that isn't. Noise generated in the output stage of an amplifier, after the gain control stage, wold not change as the gain is adjusted, for example.
He's saying that particular noise will be a constant level, no matter what the gain is *and* no matter what the input signal is. If the gain/input result in a signal that is a 1/2 the maximum possible output that fixed noise will be a greater percentage of the output than it would if either the gain or the input is increased to the point where the output signal reaches the maximum possible.
Generally amplifiers will be designed to have a very *very* low "post-amplification" noise level for exactly that reason. At minimum signal or gain settings, whatever noise there is in the output is almost certainly going to be objectionable if it is at all significant.
With a camera the post-amplification noise is almost certainly going to be so low as to be vertually insignificant for all normal ISO settings. It might well be one of the limiting factors for pseudo ISO settings obtained by digital multiplication of the ADC output.
>> Would you please explain this concept in English? I know about SNR and >> why I get more noise at a higher ISO, but I don't understand the >> difference between read noise and shot noise.
> Shot noise is [OK and inevitable] > Read noise is [ugly and somewhat avoidable, or could be...]
> 1)...Looking at it relative to absolute signal, > read noise on such cameras is greatest at > the lowest ISOs, and lowest at the higher ISOs...
> 2) ...when you decrease exposure... [absolute input] > read noise takes a greater toll than shot noise.
> 4) Only read noise has patterns in it. All those streaks and bands you > see in images come from read noise - sloppy electronics without > correction (most line patterns are correctable; manufacturers that have > them are just apathetic about quality). Shot noise is kind of nice > looking; like the actual texture of the image, especially at high pixel > densities.
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