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Comment by paweladamczuk | Hacker News Reader

I recorded two takes with exact same settings except one was ISO ~1500 and the other ISO ~3000. Shouldn't the second take be around twice as bright as the first one? The change in brightness is hardly noticeable.

I suppose this is the same case as every other camera app I've ever tested on Android and iOS, such granular settings like ISO are just not accessible by the system APIs available to the app. In that case though, I'd expect the app to at least not lie to me.

Can someone confirm or deny this? I don't know much about photography nor iOS so I might just be confused.

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You can see the brightness change when you fiddle with the ISO, so I'm not sure where you'd draw the conclusion that the system APIs don't give apps access to that.

Moving from ISO 1500 to ISO 3000 doubles the sensor's sensitivity to light, but doesn’t inherently make the scene appear twice as bright.

To add to the other commenters: when you tweak the sensors sensitivity for light, the aperture will compensate by letting less light in – unless it is fixed. So there should be no noticeable difference in brightness unless you set a fixed aperture.

This is a smartphone camera, so of course the aperture is fixed. Playing around with the app, it does not seem to automatically adjust shutter speed to match changes in ISO. Reducing the ISO does make the image darker – presumably just not as much as OP expected.

ISO is linear scale and perception is log scale. Doubling the ISO (while keeping the shutter speed the same) increases the exposure by only one stop, which won’t seem twice as bright.

Isn't "one stop" defined log-wise to be "twice as bright" perceptually?

No, it's twice as bright physically (in the sense that the lux value doubles). For example, doubling the shutter speed increases the exposure by one stop. Similarly, increasing the diameter of the aperture by a factor of √2 (thus doubling the area of the aperture and letting twice as much light in) increases the exposure by one stop.

https://en.wikipedia.org/wiki/Weber%E2%80%93Fechner_law#:~:t....

If all else is kept the same. Usually with auto exposure, it will compensate by changing the integration time ("shutter speed") or aperture in order to try and keep the exposure to the same level.

> such granular settings like ISO are just not accessible by the system APIs available to the app

...what? Every non dumbified enough app has ISO and shutter controls in the manual mode since forever.

Eg:

https://f-droid.org/en/packages/net.sourceforge.opencamera/

Remember, this is iOS. A system where apps can't even record continuous framerate footage.

>> as every other camera app I've ever tested on Android and iOS

So I assumed...

> this is iOS. A system where apps can't

picard.jpg

ISO is supposed to be the sensitivity of the film to light, and the numbers were set by a standards organisation so I'm not sure you can double the number to double the effect.

Also, how does this even work on a digital camera? Surely we can't actually adjust how sensitive the sensor is to light, so is it just a simulation?

It's complex. Many modern cameras have dual or triple gain amplifiers, with various range setups. Some ISO settings might be just a digital multiplier on the highest setting of the lower gain stage before switching to the higher gain (which may result in having better snr at higher iso for some settings).

Remember that "digital" sensors are mostly analog devices (dealing in continuous voltages).

We can configure the gain of the analog amplifiers

> Also, how does this even work on a digital camera?

It’s signal gain of the sensor.

“In digital camera systems, an arbitrary relationship between exposure and sensor data values can be achieved by setting the signal gain of the sensor. (…) For digital photo cameras ("digital still cameras"), an exposure index (EI) rating—commonly called ISO setting—is specified by the manufacturer such that the sRGB image files produced by the camera will have a lightness similar to what would be obtained with film of the same EI rating at the same exposure.”

Source: https://en.m.wikipedia.org/wiki/Film_speed#Digital_camera_IS...

Kind of the same it works on film cameras: you change the sensitivity of the emulsion on them, you change the sensitivity of the sensor by raising the gain on the others.

Or think of it like changing the gain on an microphone pre-amp before going into a Analog-to-Digital convertor.

Probably auto-exposure adjusted the shutter speed to compensate

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