2 fix spelling mistakes
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To be short ETTR is a smart usage of two fact:

  1. There is more information in the high light (the right of the level curve) than in the low light (the left of the level curve). This is due to the fact that capter havehas linear responceresponse to the light intensity while human perseptionperception is rather log (what you perciveperceive as twice brighter is in fact not twice the amount of light but much more)

  2. The noise is present everywhere but what you perciveperceive is the ratio noise over signal: if the signal is big you cannot see the noise, if the signal is of the same order or smaller than the noise you will see noise. So the more you collect light the bigger is your signal and the smaller is the noise perception

When overexposing your image (and in particular a globally dark image) you are using the right part of level curve for storing your image rather than the left one. Doing that you beneficy ofhave two advantages (1) more information (more distinct tones) and (2) by collecting more light you increase the signal/noise ratio (so get less visible noise)

In post-treatment you can then correct your level and get the tone you want.

Back to film camera (I get the B&W picture which is equivalent to the color one but easier to figured out) each grain havehas a threshold (a number of photon) above which it will turn black and bellow which it will stay white (and be washed out in the film processing) the "noise" was the size of the grain which was related to the sensitivity.

To be short ETTR is a smart usage of two fact:

  1. There is more information in the high light (the right of the level curve) than in the low light (the left of the level curve). This is due to the fact that capter have linear responce to the light intensity while human perseption is rather log (what you percive as twice brighter is in fact not twice the amount of light but much more)

  2. The noise is present everywhere but what you percive is the ratio noise over signal: if the signal is big you cannot see the noise, if the signal is of the same order or smaller than the noise you will see noise. So the more you collect light the bigger is your signal and the smaller is the noise perception

When overexposing your image (and in particular a globally dark image) you are using the right part of level curve for storing your image rather than the left one. Doing that you beneficy of (1) more information (more distinct tones) and (2) by collecting more light you increase the signal/noise ratio (so get less visible noise)

In post-treatment you can then correct your level and get the tone you want.

Back to film camera (I get the B&W picture which is equivalent to the color one but easier to figured out) each grain have a threshold (a number of photon) above which it will turn black and bellow which it will stay white (and be washed out in the film processing) the "noise" was the size of the grain which was related to the sensitivity.

To be short ETTR is a smart usage of two fact:

  1. There is more information in the high light (the right of the level curve) than in the low light (the left of the level curve). This is due to the fact that capter has linear response to the light intensity while human perception is rather log (what you perceive as twice brighter is in fact not twice the amount of light but much more)

  2. The noise is present everywhere but what you perceive is the ratio noise over signal: if the signal is big you cannot see the noise, if the signal is of the same order or smaller than the noise you will see noise. So the more you collect light the bigger is your signal and the smaller is the noise perception

When overexposing your image (and in particular a globally dark image) you are using the right part of level curve for storing your image rather than the left one. Doing that you have two advantages (1) more information (more distinct tones) and (2) by collecting more light you increase the signal/noise ratio (so get less visible noise)

In post-treatment you can then correct your level and get the tone you want.

Back to film camera (I get the B&W picture which is equivalent to the color one but easier to figured out) each grain has a threshold (a number of photon) above which it will turn black and bellow which it will stay white (and be washed out in the film processing) the "noise" was the size of the grain which was related to the sensitivity.

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source | link

To be short ETTR is a smart usage of two fact:

  1. There is more information in the high light (the right of the level curve) than in the low light (the left of the level curve). This is due to the fact that capter have linear responce to the light intensity while human perseption is rather log (what you percive as twice brighter is in fact not twice the amount of light but much more)

  2. The noise is present everywhere but what you percive is the ratio noise over signal: if the signal is big you cannot see the noise, if the signal is of the same order or smaller than the noise you will see noise. So the more you collect light the bigger is your signal and the smaller is the noise perception

When overexposing your image (and in particular a globally dark image) you are using the right part of level curve for storing your image rather than the left one. Doing that you beneficy of (1) more information (more distinct tones) and (2) by collecting more light you increase the signal/noise ratio (so get less visible noise)

In post-treatment you can then correct your level and get the tone you want.

Back to film camera (I get the B&W picture which is equivalent to the color one but easier to figured out) each grain have a threshold (a number of photon) above which it will turn black and bellow which it will stay white (and be washed out in the film processing) the "noise" was the size of the grain which was related to the sensitivity.