Bayou

WJShaheen Loc: Gold Canyon, AZ

uhaas2009

Grain-noise can be created by long exposure (heat of senior), high ISO, surroundings of your subjects. Higher ISO will lighten up your pics. With today’s digital you have more room to play with-in PP high ISO can be corrected with de-noising and re-sharpening.
The sweet spot of your camera ISO you have to try, my one body handle 6400iso pretty good but long exposure I have more noise......

johngault007 Loc: Florida Panhandle

While I am absolutely learning a ton about gain vs. ISO, which is a great discussion, I have to jump in on these two examples.

When it comes to sound, volume increases the decibel level without changing the tone of a sound wave. So basically the output decibels of a system.
gain is modifying the input signal which does change the tone of the sound (think distortion on a guitar). So the two can be used in tandem or independent of each other to get the desired tone/loudness.

Now, back to the regularly scheduled programming, because I can't necessarily apply all of that logic to photographic equipment

CaptainPhoto

So where is your scientific proof of that claim? Explain it or retract it. If you can't prove it then why say it.

SuperflyTNT Loc: Manassas VA

I see a lot if dee technical discussion here. From a functional standpoint just look at it as similar to film speed. The higher the number the less light you need but you lose dynamic range and you increase noise, (kinda like grain). Although with digital cameras the sensors keep getting better and the the ability to shoot at high a ISO with very little noise is way beyond what was capable with film. Also there are post processing tools that are very effective in dealing with noise.

frankraney Loc: Clovis, Ca.

I do not know how ISO is accomplished, but I do know the end results. But I go know you're statement is BS. If you really want to know a little truth, listen to Ysarex and you might learn something.

selmslie Loc: Fernandina Beach, FL, USA

Such a ridiculous statement hardly warrants a serious response but maybe this will clear things up for you and anyone else gullible enough to fall for that claim.

ISO was created for film in 1987 based on the definition of ASA which had been around for about four decades. ASA and ISO are the same thing for film and digital.

A daylight scene containing a neutral gray target (about 18%) exposed at 1/ISO seconds at f/16 (Sunny 16) will produce an image where the target appears to be middle gray. This is true for negative or positive film developed normally as well as digital. In both cases the contrast will also be normal although transparency film will have slightly more contrast because it was originally intended to be projected.

Digital and normally developed film both respond in the same manner to changes in exposure - shutter speed and aperture.

Digital ISO claims are more standard than they ever were for film because the effective ISO for film depends on each individual's interpretation of "normal" development.

Ysarex Loc: St. Louis

The current ISO standard for digital cameras (ISO 12232:2019) was written by the camera manufacturers. They have an organization, Camera & Imaging Products Association, http://www.cipa.jp/index_e.html that did the work and wrote and updated the current ISO standard. And of course since they produced the standard they comply with it.


The ISO standard requires that each photo's exif data contain an entry that identifies ISO standards compliance for that image -- it's there for all of us to see in every image.

Kozan Loc: Trenton Tennessee

You are right. No need to complicate the situation. One can think of it as the old ASA film speed applied to digital. I don't need to understand Maxwell's Equations to understand radio waves.

DirtFarmer Loc: Escaped from the NYC area, back to MA

Nerdy explanation of the ISO/noise relationship (without going too far into the gritty details):

Your sensor knows nothing about your ISO. It takes photos and converts them to electrons, which it stores. The number of photons depends on the intensity of the light and the time of the exposure. If you have "the right exposure" the brightest parts of your subject will produce enough electrons to max out the storage capacity of that particular pixel in the sensor. If you are overexposed, you have too many electrons so some of them will be thrown away. If you are underexposed, you will not reach the maximum capacity of the sensor.

So after the exposure your sensor has a bunch of areas with electrons stored in them. What now? You have to read out the sensor and convert the number of electrons at each pixel into a digital numeric value. You do that by taking the electrons and converting them to a voltage, which you then convert into a number. For a 12 bit sensor, the largest number you can get is 2^12, or 4096. For a 14 bit sensor, 2^14=16384.

At this point we get into the realm of statistics. For integers, the uncertainty of any counted number depends on Poisson statistics, but when the number is large enough, Poisson statistics merge into Gaussian statistics (usually around numbers greater than 10). For Gaussian statistics, the uncertainty in a given number is given by the square root of that number, generally called σ (sigma). Herein lies noise. If you have an area of uniform brightness in your image, with, say, a brightness that is converted into the number 1024, the square root of that is 32. The actual number you will get will average 1024, but can vary about that value. The variability is the noise.The variation of the number will fall within a Gaussian curve, so that ~68% of your numbers will be within σ of 1024, ~95% of your numbers will be within 2σ of 1024, ~99.7% will be within 3σ of 1024. So although your image has an area of uniform brightness in real life, your camera will show it with some brightness variations. For this example, σ is about 3% of the brightness. If your uniform brightness area is not so bright and only gives you 128 electrons instead of 1024, σ will be 16. So now σ is about 6% of the brightness, and you will see more variability, i.e. more noise. So noise is going to depend on the number of electrons your sensor is storing.

Now we have to consider what ISO does.

Raising the ISO basically multiplies the number that is derived when you read out the electrons from your sensor. It might just use an analog approach, in which the voltage derived from the number of electrons is raised by changing the amplification, or a digital approach in which the number derived from the number of electrons is just multiplied by a constant. Neither of these approaches will change the relationship between the final number and the variability of that number from the initial statistics.

The advantage of raising the ISO is that you can use shorter exposures to get what looks like good exposures in terms of numbers coming from the sensor readout. That means you can use a higher shutter speed to reduce motion blur, or a smaller aperture to increase depth of field. Modern cameras probably apply image processing software to reduce the noise so it will not look so bad, but that cannot eliminate the noise.

There are other sources of noise, not considered here, but they are small in normal conditions.

Ysarex Loc: St. Louis

The standard is published and transparent and available for everyone to see. The standard requires the camera manufacturer to place and entry in the photo's exif data noting ISO compliance. The camera makers do follow the standard. Your inability, refusal or whatever problem to understand the standard isn't their problem.



That's debatable but regardless that's also your arbitrary requirement. The fact that the camera makers didn't check with you first and get your approval of the ISO standard doesn't make the standard a lie. I have digital cameras from 4 different camera makers and they all comply with the ISO standard very well.

rmalarz Loc: Tempe, Arizona

The formula for basic exposure is:
Define Zone V - middle gray

Square Root of the ISO = the basic f-stop (key stop)
Shutter speed = 1/luminance in candles/ft^2

Using, for example, an ISO of 125, the key stop is f/11 (closest value to the square root of 125)
Thus, "at the key stop, the correct shutter speed in seconds to expose a given luminance on Zone V is the reciprocal of the luminance expressed in candles/ft^2". If the surface measured 60 cd/ft^2, the shutter speed would be 1/60 sec.

Note this is not 1/ISO. Your sunny 16 implies an ISO of 256. Thus, and exposure of 1/250 at f/16 would render a luminance value of 250cd/ft^2 as middle gray. That may work, but maybe not.
--Bob

bleirer

Very informative post, thanks! I believe I've heard you say in prior discussions that the standard is for jpeg output only, and that raw can vary from the reported, and sometimes camera companies will leave some headroom to avoid blowing highlights?

rmalarz Loc: Tempe, Arizona

"For a 12 bit sensor, the largest number you can get is 2^12, or 4096. For a 14 bit sensor, 2^14=16384."

And that's why I love mine at 65536.
--Bob