ISO Is Not Fake and Tony Northrup Is Wrong

A few days ago, camera industry guru Tony Northrup published a video arguing that in the age of digital photography, ISO is effectively meaningless and that it’s no different from dragging the exposure slider in Lightroom. Photographer Dave McKeegan has offered a response and argues that Northrup’s logic is completely wrong.

Like many others responding to Northrup’s video, McKeegan’s point hinges on the fact that the camera, in processing the signal from the sensor, is multiplying that data before it is converted from analog data into digital data. This is what Fstoppers' own Lee Morris was suggesting might be happening when performing his own tests last week, albeit without knowing the science behind it.

In effect, the exposure slider in Lightroom is dealing with completely different information than a camera’s ISO setting, thus creating a different outcome. As one of the comments on Northrup’s original video observes, sensor signal is to raw as raw is to JPEG. Essentially, exposing incorrectly and relying on editing software is definitely not recommended as a means of exposing your digital images, and adjusting your camera’s ISO setting is a better option.

If you’re interested in the technological aspects, be sure to watch all of McKeegan’s video. Beyond that, if you’re still keen to know more, you might want to deep dive into the comments on both videos. You will almost certainly want to check out the comments made in response to the Fstoppers article, paying particular attention to informed contributions from community members Gary Gray and Paul Gosselin.

Whatever the outcome of this discussion, it’s useful to have an awareness of how cameras and editing software deals with information differently, as well as having an insight into how ISO functions as an industry standard, albeit with various hangovers from the film era.

Log in or register to post comments

62 Comments

Previous comments
Bodkin's Best's picture

You didn't go into much detail when you mentioned it. You just skimmed over the point and focused on backing up your hypothesis (which is good). But it does lead to people making a fuss because you didn't spend half the video talking about that point.

"Try and please everyone and no one will like it."

Ariel Martini's picture

The video is 100% accurate, but the clickbait title got people confused

Clickbait titles are his standard procedure.

Your title isn't at all nuanced as you make it out to be. You claimed that all ISO is fake.

stop back pedaling and own up to your lack of nuance and clickbait title...

I'm an academic. If you do a double-blind randomized study and find an effect in a subset of the data (for example, epithelial cells stop dividing after 70 divisions), you don't write an article claiming all the data follows that rule, even if it's only in the title (CELLS STOP DIVIDING AFTER 70 DIVISIONS). While it's technically true, it's also not. It applies to a small subset of cells and if you pulled of that shit in a serious setting, you'd be out of a job in no time. But hey, lucky you, you're not an engineer, but a youtube person. Just remember that.

So maybe you can pull that shit off for the general public (people are morons on average), but you should know that there are more knowledgeable people than you that look at your stuff and - laugh. Yes, they laugh. Your reputation in high-end circles (and I can vouch for that because I'm part of them) is laughable. You're a meme, Tony.

Jerome Brill's picture

I understand the arguments but it doesn't change the fundamentals of digital photography and taking a well exposed photograph.

michaeljin's picture

Devils Advocate: It kind of does when you realize that this is no longer standardized and that the in-camera meter is lying to you to exaggerate manufacturers' claims. Trying to take a well-exposed photograph with a meter that isn't set to any actual standard is like measuring things with a ruler that uses the manufacturer's proprietary definition of inches or centimeters. Of course you'll probably adapt to it as long as you keep using the same ruler just like you'll learn to compensate for your camera, but it's stupid for there to be variance across manufacturers in the first place. ISO 400 should mean ISO 400 whether you're shooting Canon, Nikon, Sony, Fuji, Leica, or a Mickey Mouse Camera.

Ed Sanford's picture

The key word is "should". The fact is that it doesn't. I come from the telecommunications world. Most service providers built their networks by clustering equipment from the same vendor in network nodes. This was true even though the equipment from all vendors was built to the same standard specifications. It was too much risk mixing equipment because individual manufacturers handled signals differently. I believe that standards organizations try to get things roughly right, but there will always be a lack of precision.

David Penner's picture

This is true with any electronics really. Just look at ram. Typically if you want 32 gigs of ram for your system you buy a 32 gig kit since if you buy 16 gigs now and grab another 16 gigs later you can't guarantee they will play nice together even when you buy the same brand and series.

michaeljin's picture

The difference on a modern sensor is close enough that it doesn't matter all that much unless you're planning to blow up a print to some absurd size and look at it at nose distance. Nobody is going to watch Tony's video and suddenly go out and start purposely underexposing their images by 5 stops either so i think we can all stop getting our panties in a twist over minor details.

Francisco Eduardo de Camargo's picture

Tony used a Nikon camera for his test, it must have been the D850. If you do this test with any Canon camera the results will not be the same. There are sensors and sensors and each one will bring different results to this approach.

Rashad Hurani's picture

I more liked the "senators" one!

Can we please, please, please, stop using those obnoxious facepalm expressions in video thumbnails? If you want to challenge the guy's argument, fine, but do you need to be so patronizing about it?

Kirk Darling's picture

Sounds to me like we each need to calibrate our own equipment and our own method of processing the images--like back in the Zone days. At least cameras these days keep their own exposure notes.

Mark Richardson's picture

Maybe just go out and make images instead of videos about something so unimportant. Man, I sound grouchy.

Motti Bembaron's picture

Watched both and learned from both. Very interesting and educational. I am definitely going to do a test on all my cameras and see for myself.

Rob Mitchell's picture

Bottom line. Does it really matter?
Yes? Carry on discussing.
No? Carry on making images.
I’m off to do a job. Invariant variant boosted non boosted ISO, or whatever.

marc gabor's picture

Great video. Simple explanation of a question I've pondered many times. Essentially he's describing signal to noise ratio. In the audio world clipping your signal is like clipping highlights - you can never get them back. Does it make sense to record at a conservative gain and boost later if necessary (not all amplifiers or RAW converters being created equal)? yes. Does it make sense to record a unnecessarily low signal and in turn amplify all the noise incurred along the signal path? No. A 24 bit 192k audio recording has a much lower signal to noise ratio than tape which allows you to cleanly record very low signals. Digital cameras today also have very low signal to noise ratios that allow us to not only shoot in the dark but also give us a comfortable cushion that allows us to preserve the highlights and boost the brightness without any noticeable degradation in image quality. Good times.

Apologies for the long post, I just could not find a better way to illustrate the point. (And, whether it is necessary to say or not, I have an engineering background in electronics and computer science.)

I have a deep respect for Tony Northrup and Dave McKeegan, but neither mentioned the fact that the analog signal has many more levels of charge than the digital file can record as the A/D (analog to digital) converters have a limited number of bits (up to, I think, 14 for the best cameras at the moment, which can record 16 384 different levels of light from 0 = black to 16 383 = white — assuming a black and white only sensor, but the same goes for each colour of an RGB sensor). The sensor may be able to literally generate millions of different levels of charge per pixel, but these analog levels of charge are binned into groups by the A/D converter to prevent the digital images from becoming too big and because high-speed A/D converters are much more difficult to construct the more bits they have.

To illustrate the difference between analog boosting of ISO and digital boosting, think of a hypothetical, non-ISO-invariant camera that has a 2-bit A/D converter, which means a digital image could show four different levels of lightness per pixel: 0 = black, 1 = dark grey, 2 = light grey, and 3 = white. The camera's sensor has four pixels that can record 16 levels of charge each, where 0 = black, 15 = white and the other levels are different shades of grey. In the conversion analog levels 0, 1, 2, 3 become 0 = black in the resulting digital file; analog levels 4, 5, 6, 7 become 1 = dark grey in digital; analog levels 8, 9, 10, 11 become 2 = light grey digitally; and analog levels 12, 13, 14, 15 become 3 = white digitally.

This camera records an underexposed image where the analog charge levels are
Pixel 1: 2
Pixel 2: 5
Pixel 3: 6
Pixel 4: 7

When converted into a digital raw image, these pixels get the following values:
Pixel 1: 0
Pixel 2: 1
Pixel 3: 1
Pixel 4: 1

Trying to get a better result, we could do as Tony Northrup suggests, enhance the digital raw image, in this case by multiplying by two (one stop), resulting in the following digital values:
Pixel 1: 0
Pixel 2: 2
Pixel 3: 2
Pixel 4: 2

The resulting digital image, just as the underexposed digital image, does not show much detail, as the differences between the analog values of pixels 2, 3, and 4 are lost.

Boosting the analog signal by a factor of two (one stop) instead would result in the following analog values:
Pixel 1: 4
Pixel 2: 10
Pixel 3: 12
Pixel 4: 14

Converted to digital:
Pixel 1: 1
Pixel 2: 2
Pixel 3: 3
Pixel 4: 3

Three different values in the output of the analogly boosted image means it has more detail than the digitally boosted image with only two different values. The difference between the two would clearly be much more obvious if we had more pixels and more values to choose from, but I think I may have used enough space here as it is.

Paulo Macedo's picture

Thank you fellow engineer. This comment should be the whole article.
Maybe a few classes of Digital Systems would help a lot of photographers not to swallow every "truth" they see on the web.

Terry Waggoner's picture

Damn.........now I got a headache................(teasing)

In most cameras, the quantization rounding is lower than the noise level and is not the dominant issue.

See https://photographylife.com/iso-invariance-explained for a good discussion. In short, there is a combination of 1/ actual iso invariance because cameras achieve high ISO digitally rather than with analog gain, 2/ the backend noise (noise that occurs after analog amplification) is very low on modern cameras and therefore high ISO don't have that much to save by not amplifying that noise.

David Pavlich's picture

After reading the articles, watching the videos, and reading the comments, my conclusion is that I'll continue to shoot the same way I did before this all came to light. :-)

imagecolorado's picture

I never heard of Tony until he got popular spouting BS. Now, I just skip on past. At least he is more interesting than Ken Rockwell.

Kjell Vikestad's picture

The sensor does not change sensibillity. If you adjust the iso from 100-400, this will not make the sensor four times more sensibel to light. The magic happends when the information from the sensor is prosessed in the camera into raw- or jpg files. This is also why different camerabrands with the same sensor will not look the same. Different prosessing of data from the sensor.
This si altso why photoshop, lightroom etc can not give the same result as in camera prosessing. These programs only get the raw files to work with, and these data is already prosessed in the camera. But if these programs could get data direkt from the sensor, they could in theory produse the same quality.
So in theory you could take all pictures at iso 100, and adjust the iso later in the computer. This would only be possible if you could get real «raw» data from the sensor, and not the prosessed raw file like today.

To understand optics and digital sensors, you need to do that math. And the math is not trivial. And by the way, mirrorless cameras are terrible.

Michal Wachfaitl's picture

Garden test where I have apparently skipped ISO 200 :) with ten years old full frame camera; in every case, the results do not look same at all...mainly right curtain area is horrible when shot on lower ISOs pulled up afterwards.
RAWs processed in Lightroom without a touch, composed and exported in PSP, JPG 85%.

More comments