IŽd like to know about the signal to noise ratio of my digital camera.
According to a website I found this value is the ratio of total signal
to total noise expressed in decibels (dB) and can be calculated with
the following formula:
SNR = 20 log (Signal RMS / Noise RMS)
As math was always a horror for me, I have only a slight idea of "root
mean square" but donŽt know how to deduce those values from simple
digital images. Can someone please help me with that?
On May 22, 5:28*am, Marc Wossner <marc.woss...@gmx.net> wrote:
> Hi ng,
>
> IŽd like to know about the signal to noise ratio of my digital camera.
> According to a website I found this value is the ratio of total signal
> to total noise expressed in decibels (dB) and can be calculated with
> the following formula:
>
> SNR = 20 log (Signal RMS / Noise RMS)
>
> As math was always a horror for me, I have only a slight idea of "root
> mean square" but donŽt know how to deduce those values from simple
> digital images. Can someone please help me with that?
>
> Best Regards!
> Marc Wossner
db is sound not what your eve sees, what is "this wedsite" for you id
say tb, trollbell
On 22 Mai, 12:36, ransley <Mark_Rans...@yahoo.com> wrote:
> On May 22, 5:28*am, Marc Wossner <marc.woss...@gmx.net> wrote:
>
> > Hi ng,
>
> > IŽd like to know about the signal to noise ratio of my digital camera.
> > According to a website I found this value is the ratio of total signal
> > to total noise expressed in decibels (dB) and can be calculated with
> > the following formula:
>
> > SNR = 20 log (Signal RMS / Noise RMS)
>
> > As math was always a horror for me, I have only a slight idea of "root
> > mean square" but donŽt know how to deduce those values from simple
> > digital images. Can someone please help me with that?
>
> > Best Regards!
> > Marc Wossner
>
> db is sound not what your eve sees, what is "this wedsite" for you id
> say tb, trollbell
Yes, but "db" is also quite often used in electronic context as well
so I thought id would be correct.
If it isn`t, can you tell me the right way?
On May 22, 6:10*am, Marc Wossner <marc.woss...@gmx.net> wrote:
> On 22 Mai, 12:36, ransley <Mark_Rans...@yahoo.com> wrote:
>
>
>
>
>
> > On May 22, 5:28*am, Marc Wossner <marc.woss...@gmx.net> wrote:
>
> > > Hi ng,
>
> > > IŽd like to know about the signal to noise ratio of my digital camera.
> > > According to a website I found this value is the ratio of total signal
> > > to total noise expressed in decibels (dB) and can be calculated with
> > > the following formula:
>
> > > SNR = 20 log (Signal RMS / Noise RMS)
>
> > > As math was always a horror for me, I have only a slight idea of "root
> > > mean square" but donŽt know how to deduce those values from simple
> > > digital images. Can someone please help me with that?
>
> > > Best Regards!
> > > Marc Wossner
>
> > db is sound not what your eve sees, what is "this wedsite" for you id
> > say tb, trollbell
>
> Yes, but "db" is also quite often used in electronic context as well
> so I thought id would be correct.
> If it isn`t, can you tell me the right way?
>
> Best regards!
> Marc Wossner- Hide quoted text -
>
> - Show quoted text -
I went to www.dpreview.com and typed in a search of Decibel, and it is
one measure used. But db was developed as a rating of sound. I have
no idea how its transfered to a visual rating, or number, if it even
is as sound can be easily rated in S/N and db numbers, which are easy
to understand and industry accepted. I dont see any db ratings at
dpreview, just visual detail charts and descriptions. It would make
buying equipment easy if numbered ratings on a large known scale were
assigned to cameras and lenses as is done in audio equipment. Is it
done with dvds on the video portion? It is done with sound ratings. To
compare your camera find sites that reviewed it, what camera is it.
On May 22, 5:28 am, Marc Wossner <marc.woss...@gmx.net> wrote:
> Hi ng,
>
> IŽd like to know about the signal to noise ratio of my digital camera.
> According to a website I found this value is the ratio of total signal
> to total noise expressed in decibels (dB) and can be calculated with
> the following formula:
>
> SNR = 20 log (Signal RMS / Noise RMS)
>
> As math was always a horror for me, I have only a slight idea of "root
> mean square" but donŽt know how to deduce those values from simple
> digital images. Can someone please help me with that?
>
> Best Regards!
> Marc Wossner
Unfortunately, the handling of logrithmic values is not the hardest
part of the job. In order to really look at signal to noise, you need
to make a very carefully controlled exposure, and look at lots of
pixels in order to get a statistical value of each part (signal and
noise). Also, there are a couple of types of snr definitions (large
signal vs small signal snr).
You should also be looking at a RAW file, since the jpeg compression
affects snr of an image.
the root mean square part is easy.
Look at a large range of noise pixels, say at least 10. Compute the
average. Then go back to the individual readings, and subtract the
average from each. Then square the differences. Add together all
these "squares". Now take the square root of the sum of the squares.
Many calculators can do this part. In fact, some scientific and most
statistical calculators can compute the RMS by entering a series of
readings.
ransley wrote:
><snip>
>
> I went to www.dpreview.com and typed in a search of Decibel, and it is
> one measure used. But db was developed as a rating of sound. I have
> no idea how its transfered to a visual rating, or number, if it even
> is as sound can be easily rated in S/N and db numbers, which are easy
> to understand and industry accepted. I dont see any db ratings at
> dpreview, just visual detail charts and descriptions. It would make
> buying equipment easy if numbered ratings on a large known scale were
> assigned to cameras and lenses as is done in audio equipment. Is it
> done with dvds on the video portion? It is done with sound ratings. To
> compare your camera find sites that reviewed it, what camera is it.
From Wikipedia:
The decibel (dB) is a logarithmic unit of measurement that expresses the
magnitude of a physical quantity (usually power or intensity) relative
to a specified or implied reference level. Since it expresses a ratio of
two (same unit) quantities, it is a dimensionless unit. A decibel is one
tenth of a bel (B).
The decibel is useful for a wide variety of measurements in science and
engineering (e.g., acoustics and electronics) and other disciplines. It
confers a number of advantages, such as the ability to conveniently
represent very large or small numbers, a logarithmic scaling that
roughly corresponds to the human perception of, for example, sound and
light, and the ability to carry out multiplication of ratios by simple
addition and subtraction.
And why did you go to a digital camera review site to look up a
scientific term?
On Thu, 22 May 2008 07:21:17 -0700 (PDT), Don Stauffer in Minnesota
<stauffer@usfamily.net> wrote:
>On May 22, 5:28 am, Marc Wossner <marc.woss...@gmx.net> wrote:
>> Hi ng,
>>
>> IŽd like to know about the signal to noise ratio of my digital camera.
>> According to a website I found this value is the ratio of total signal
>> to total noise expressed in decibels (dB) and can be calculated with
>> the following formula:
>>
>> SNR = 20 log (Signal RMS / Noise RMS)
>>
>> As math was always a horror for me, I have only a slight idea of "root
>> mean square" but donŽt know how to deduce those values from simple
>> digital images. Can someone please help me with that?
>>
>> Best Regards!
>> Marc Wossner
>
>Unfortunately, the handling of logrithmic values is not the hardest
>part of the job. In order to really look at signal to noise, you need
>to make a very carefully controlled exposure, and look at lots of
>pixels in order to get a statistical value of each part (signal and
>noise). Also, there are a couple of types of snr definitions (large
>signal vs small signal snr).
>
>You should also be looking at a RAW file, since the jpeg compression
>affects snr of an image.
>
>the root mean square part is easy.
>
>Look at a large range of noise pixels, say at least 10. Compute the
>average. Then go back to the individual readings, and subtract the
>average from each. Then square the differences. Add together all
>these "squares". Now take the square root of the sum of the squares.
>Many calculators can do this part. In fact, some scientific and most
>statistical calculators can compute the RMS by entering a series of
>readings.
>
>Now you can convert your ratio into dbs.
Rawnalyzer, a freeware program, will calculate the min, max, mean, and
standard deviation of a mouse-selected square of pixels in a raw file.
It does it separately for R,G,B, and overall. The standard deviation
of a uniform neutral exposure would be equivalent to RMS noise. The
denominator for SNR would then be the range available in the raw file
- 4096 for 12-bit or 16384 for 14-bit. This program will take the
drudgery out of the calculations, if not out of getting the careful
exposures. http://www.cryptobola.com/PhotoBola/Rawnalyze.htm
On Thu, 22 May 2008 10:15:06 -0500, John O'Flaherty
<quiasmox@yeeha.com> wrote:
>On Thu, 22 May 2008 07:21:17 -0700 (PDT), Don Stauffer in Minnesota
><stauffer@usfamily.net> wrote:
>
>>On May 22, 5:28 am, Marc Wossner <marc.woss...@gmx.net> wrote:
>>> Hi ng,
>>>
>>> IŽd like to know about the signal to noise ratio of my digital camera.
>>> According to a website I found this value is the ratio of total signal
>>> to total noise expressed in decibels (dB) and can be calculated with
>>> the following formula:
>>>
>>> SNR = 20 log (Signal RMS / Noise RMS)
>>>
>>> As math was always a horror for me, I have only a slight idea of "root
>>> mean square" but donŽt know how to deduce those values from simple
>>> digital images. Can someone please help me with that?
>>>
>>> Best Regards!
>>> Marc Wossner
>>
>>Unfortunately, the handling of logrithmic values is not the hardest
>>part of the job. In order to really look at signal to noise, you need
>>to make a very carefully controlled exposure, and look at lots of
>>pixels in order to get a statistical value of each part (signal and
>>noise). Also, there are a couple of types of snr definitions (large
>>signal vs small signal snr).
>>
>>You should also be looking at a RAW file, since the jpeg compression
>>affects snr of an image.
>>
>>the root mean square part is easy.
>>
>>Look at a large range of noise pixels, say at least 10. Compute the
>>average. Then go back to the individual readings, and subtract the
>>average from each. Then square the differences. Add together all
>>these "squares". Now take the square root of the sum of the squares.
>>Many calculators can do this part. In fact, some scientific and most
>>statistical calculators can compute the RMS by entering a series of
>>readings.
>>
>>Now you can convert your ratio into dbs.
>
>Rawnalyzer, a freeware program, will calculate the min, max, mean, and
>standard deviation of a mouse-selected square of pixels in a raw file.
>It does it separately for R,G,B, and overall. The standard deviation
>of a uniform neutral exposure would be equivalent to RMS noise. The
>denominator for SNR would then be the range available in the raw file
The numerator, I mean.
>- 4096 for 12-bit or 16384 for 14-bit. This program will take the
>drudgery out of the calculations, if not out of getting the careful
>exposures.
>http://www.cryptobola.com/PhotoBola/Rawnalyze.htm
John O'Flaherty wrote:
[]
>> - 4096 for 12-bit or 16384 for 14-bit. This program will take the
>> drudgery out of the calculations, if not out of getting the careful
>> exposures.
However, do be aware that a simple SNR calculation will tell you very
little about the performance of the camera, unless you take the MTF into
account. You could make a camera with a low high-frequency MTF which you
have a very high SNR, but produce very blurry images. You really need to
measure the SNR for a known input at a known spatial frequency, and then
weight that measurement according to the perception characteristics of the
viewer.....
On Thu, 22 May 2008 17:01:38 GMT, "David J Taylor"
<david-taylor@blueyonder.neither-this-bit.nor-this-bit.co.uk> wrote:
>John O'Flaherty wrote:
>[]
>>> - 4096 for 12-bit or 16384 for 14-bit. This program will take the
>>> drudgery out of the calculations, if not out of getting the careful
>>> exposures.
>
>However, do be aware that a simple SNR calculation will tell you very
>little about the performance of the camera, unless you take the MTF into
>account. You could make a camera with a low high-frequency MTF which you
>have a very high SNR, but produce very blurry images. You really need to
>measure the SNR for a known input at a known spatial frequency, and then
>weight that measurement according to the perception characteristics of the
>viewer.....
Good points. Simply taking the maximum channel value as reference
would give you a best possible SNR. With a scene that uses less than
the full dynamic range of the sensor or a lens that has MTF
limitations or flare that limit achievable contrast, the photo's SNR
would be worse too. As you point out, performance is more complicated
than just noise.
Calculation of snr 
Linear Mode
