Why 'more or less stopped using ISO'?

Started Feb 19, 2014 | Questions thread
bobn2 Forum Pro • Posts: 52,299
Re: Why 'more or less stopped using ISO'?

D Cox wrote:

bobn2 wrote:

edhannon wrote:

There are three places that brightening can be applied:

  • With amplification between the sensor andq analog to digital conversion (e.g. Pentax *ist line)

That doesn't apply any 'brightening', it just makes the voltage representing a particular photo-electron count bigger.

Which will give a larger number when digitised, which will give a brighter image.

Well the depends entirely on the digitisation scale. Take the voltage and feed it into a 12 bit ADC it will give you a smaller number than if you feed it into a 14 bit ADC 9assuming the same reference voltage). All you are looking at is coding, not what is represented. What is represented is a count of photons, however you code it does not change what is represented.

  • By using more bits in the analosg to digital conversion than are used in raw output file then bit shifting in firmware (e.g. Pentax K10)

That doesn't apply any brightening, it just changes the code used to represent a particular photoelectron count.

  • By processing the raw data either in camera or in the raw converter.

That is the only time 'brightness' is established.

This and the last are both simple operations on the numbers. You are making a false distinction.

I'm not, I'm making a fundamental distinction about what these numbers represent. The number in the output file doesn't represent an absolute number of photons at all, because that number depends entirely on the display device.

The last one uses cheaper hardware but results in loss of effective bit depth.

Only the last one is brightening.

In which case your use of the word "brightness" is not helpful for understanding digital photography.

Actually, it is very useful. It avoids one indulging in the fallacy that what we have in photographic image formation is a function from photon count to photon count.

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