High ISO does NOT cause NOISE! (but f/Stop & Shutter do!)

Tony then presents an entirely new way to think about ISO. Instead of thinking of it as a camera control, think of it as a measurement of noise. It's more like a speedometer than an accelerator; if you're experiencing high noise, don't reduce your ISO. Instead, find ways to get more light to your sensor by using a longer shutter speed, a lower f/stop number, a faster lens, turning the lights up, or adding a flash.

[TonyAndChelsea]

"THE NOISE IS CAUSED BY UNDEREXPOSURE" or "THE NOISE IS CAUSED BY RAISING THE BRIGHTNESS IN POST"

Many of us (myself included) have previously been taught that high ISO does cause high noise, and it's much harder to unlearn a concept than it is to learn it for the first time. Here's a nerdy summary for my more technical audience:
First, make sure you understand the difference between causation and correlation. In a car, your speedometer *correlates* with your speed, it does not cause it. Your accelerator *causes* your speed.
High ISO *correlates* with high noise. If you're using high ISO with a properly exposed picture, your image is going to be noisy... However, lowering your ISO does not lower the noise, just like forcing down the needle on your speedometer doesn't slow your car.
Low light *causes* high noise. Regardless of the ISO, regardless of the exposure, pictures with less light will have more noise than pictures with more light. Therefore, if you want to reduce noise, add light.
What I hope to accomplish by demonstrating the difference between correlation and causation is to change how we think about ISO... MANY photographers in low-light situations limit themselves to a low ISO, like ISO 800, because they incorrectly believe that choosing a high ISO will increase their noise. Instead, they get an underexposed picture that has the same amount of noise (but requires additional processing). Hopefully, this lesson teaches those photographers that they only way to reduce noise is to increase the light their sensor is getting.
I would also like all photographers interested in technical image quality (noise, sharpness, dynamic range) to be conscious of using giving their sensor as much light as it can handle - and using auto ISO as a measurement is a good way to do this. If you're camera isn't choosing the base ISO for the exposure, then you're not getting your camera's maximum image quality. You can't always add more light, but it's a good to quickly note, "Oh, I'm at ISO 200 - can I use a longer shutter or a wider aperture to get myself down to a proper exposure at ISO 100? Can I add light in some other way?" One stop more light improves image quality about as much as upgrading from APS-C to full-frame.

[brianayala]

“The fourth corner of the exposure triangle.”

[rodrigodepierola]

TONY: "People haven't hated me enough during this lockdown, what sould I do?"

[extrashot]

It’s not film…it’s an electronic camera with adjustable gain.  This is effectively an amplification circuit which is amplifying the signal coming off the sensor.  What you’re talking about is signal to noise ratio.  Obviously, if you have plenty of signal (light) you have less noise… less signal, more noise.  It’s simple… and nothing like a speedometer.  Also proving your point with a dual base ISO camera just confuses the argument totally.

[gregfaris]

ISO, beyond the basic sensitivity level of your sensor (usually 100-200) is a gain amplification applied to the signal coming from the sensor. If you use it to compensate underexposure, instead of using the real exposure parameters (duration and aperture) it will definitely amplify noise.

[Sebabarrossierz]

Jared Polin Is going to dislike this 👍

[DavidFricks]

Tony just blew my mind! In the audio industry we often refer to this as signal to noise ratio. I now realize the sensor noise is static, and that the iso setting is just adding gain. I never realized how much photography has in common with audio engineering until now. Light is a wave just like sound. My camera is a transducer just like a microphone, so all the rules of reflection, absorption, and distance (inverse square) apply.

[notgazo]

Hello,
An automation engineer here with some knowledge of signal processing. I don't agree with your explanation: there is always noise, but amplifying the signal to properly expose an image increases its visibility, nothing else. The true exposure is defined by the light transmission of a lens (approximated by the diaphragm) and the exposure time (shutter speed). The camera can also have several basic sensitivity levels: simply take the signal power spectrum of an image and apply a gain to it. You can amplify the signal by using a higher ISO in your camera or in post-production, but the result is very similar with the raw format. But it's usually best to do it as close to the source as possible to avoid adding transmission noise before amplification and to work with the actual analog information and not with the digital information that has already lost some of it due to the quantization process.

[GordLamb]

A few points for people still confused about this:


1. When we say "noise" we generally mean perceptible noise. Grain we can see. All sensor readouts contain noise (the noise floor of the signal). It's only a problem when we can perceive it. At the levels we deal with in photography, it's caused by a few things, but mainly the random quantum behavior of photons, and electronic readout noise.


2. Dynamic range is the difference between the brighest part of the image and the noise floor. When a sensor is underexposed, this difference - the dynamic range - is smaller. The noise is still there, but it's too dark to see. However, a smaller dynamic range means a larger gain is required, and that gain applies to both the parts of the image we want (the signal) *and* the noise.


3. On mirrorless/DSLR cameras, ISO knobs usually apply gain before the camera's image processor gets the data. The exposure slider in post does the same thing, but after. On some cameras, ISO gain happens during the analog stage, which can reduce the effects of read noise, but most cameras *generally* have low read noise. In any case, applying gain with the ISO knob or in post makes very little difference when we're talking a few stops (ie. ISO200->ISO800 or +2eV).


4. The effect of adjusting ISO is different depending on your camera's mode. I think this is the key that has most folks confused. If you use your camera's automatic modes (program mode, aperture priority, shutter speed priority, etc) then raising ISO *will result in more perceptible noise* because your camera will underexpose the sensor. It is this underexposing which results in a lower dynamic range, lower signal:noise ratio, and more perceptible noise after gain is applied.


5. In manual mode, the only thing that affects perceptible noise is dynamic range, and this is determined by your exposure, not your ISO.


The noise is always there. It's part of sensing our world. It's only a problem when we can perceive it, and that only happens when we amplify it. We only amplify it because the bright parts of the image aren't bright enough, and this only happens because we underexpose the sensor. The same is true in the audio world: in audio, we don't call it ISO, we just call it gain. When you turn the gain on a microphone up, you hear a hiss. That's noise, amplified. You can speak more quietly (akin to underexposing a camera sensor), but will acheive a higher signal:noise ratio with less hiss when you turn down the gain and speak more loudly (akin to a proper exposure).


Lastly - this is not something to get worked up about. These are subtle differences for camera and math nerds. We find them interesting, but at the end of the day, it's the art that counts. If you still don't understand the point Tony's trying to make, then don't worry about it! Composition, storytelling and emotion are far more important than the details of how cameras calculate numbers from a bunch of voltages. :)

[sctm]

For all non-technical people: it's the low signal to noise ratio (SNR) that ruins your picture, not the boosted gain that is applied to make the image brighter.

[vladradu]

Exposure is determined solely by shutter speed, lens aperture, and scene luminance. Insufficient exposure will make more noise visible. To get less noise, you have to raise the exposure. ISO just maps an exposure to a desired lightness.

[toddmcgowan]

I have to say, that I was very skeptical of your premise, however, I just got done performing the same procedures you showed, and I was shocked to get the same results with my D800!! Thank you and your wife for all the hard work and effort you put into these videos!!

[wndache]

If you a confused, the point Tony is trying to make is if you are shooting in the dark and already have aperture and shutter speed maxed out, lowering the ISO won’t do you any good in noise reduction. You need to physically get more light in the scene. Thanks for the tip Tony, I remember trying to reduce ISO thinking the darker image will have less noise when I brighten it in post before.

[mokeydmeeple]

The lack of a greeting made me hear the opening as “Hi, ISO.” 😂

[magottyk]

0:43 uses dual gain sensor to show high ISO doesn't introduce noise in comparison to a low ISO image corrected in post with the high ISO image clearly superior in the low-mid tones.
DOH!
An apples to oranges comparison where the sensor is not operating with the same parameters, effectively being a completely different sensor with regards to dynamic range due to the gain applied at the sensor and not after the ADC conversion as is usually the case for these types of comparisons (digital gain).
Given that there are many strategies with regards to gain, it cannot be claimed as a universal that ISO settings are effectively noise neutral to the output when your first example clearly demonstrates that this is not the case.

[TLDF]

Wrong title. Should lower exposure cause more noise

[chrisfor]

Great video. The reason high ISO (or ASA for us old people) film lead to grainy images is because the silver halide grains in the film were physically larger than the grains in lower ISO film. I love nerding out on things like that.

[danev]

This is one of Tony's "duh!" videos. Raising ISO to avoid slow shutter speeds or to avoid large apertures essentially is underexposing a photo. So it is the same as taking an underexposed photo into Lightroom and increasing the Exposure slider. It turns out that more expensive wide-aperture lenses and/or Lens stabilization (to allow for a slower shutter speed) and/or tripods all allow for an exposure with the right amount of light. Anything else is using ISO as a cheat that will bite you later down the workflow. From other videos on YouTube, all sensors produce noise every time you take a picture. The more real light you are able to obtain during the exposure overrides that noise more and more (called signal to noise ratio). And yes, larger sensors do indeed have a lower native noise level than smaller sensors, all other things being equal.

[frederikboving]

Your sensors sensitivity to light is fixed. It cannot be changed in any way. How much light reaches your sensor is determined (camera wise) by aperture and shutter speed. If little light reaches your sensor, the signal to noise ratio goes up as the sensor starts to mis-read the vague light. ISO is a factor the processor/software of your camera applies to the readings of the sensor. High ISO when used to compensate for lack of light will hence amplify the noise that is already there. So the little word "cause" is the debate here. In my mind, high ISO does not cause noise as such but will amplify it if present. So if you shoot with auto ISO on and the ISO value goes ballistic then you know light is missing. I think that is Tony's point. And a good one. So see the ISO as the canary in a coal mine. And don't worry about all the tech stuff.

[ErickWright]

The first thing I said to myself was here we go again Tony hehe