Just to put this to bed. A useful reference to matters exposure is the Basic Photographic Sensitometry Workbook from Kodak. This from page 2:
June 16, 2023
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Are you being deliberately silly?
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seriously what is it ? should we just say subject/ scene luminance then ?
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Confusion between two things here.
'Exposure' refers to how much light there is (per unit area) at the plane of focus (on the sensor or film).
It's usually given by text books as E = I×t or more recently H = E×t, Where 'E' (old) or 'H'(new) means exposure, 'I' (old) or 'E' (new) means illuminance or 'brightness' at the plane of focus and t means exposure time (or 1∕'shutter speed'). The illuminance at the plane of focus is controlled by the scene luminance and the f-number.The combination of the f-number and exposure time is called the 'Exposure Value', not the 'exposure'.
I know these terms get mixed up, but mixing them up just causes confusion and an opportunity for rogues like Don to cause the havoc he likes.
Exposure is determined by scene luminance -
but its irrelevant when your taking a portrait of a black person or a white person, i set the exposure and scene lighting the same even though the
reflective light hitting the camera sensor is not the same, so how can there be a reference for lux to photography ? -
Exposure is not determined by scene luminance. scene luminance is what we are taking an Exposure of. 😉😁
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OK. Think of a painting. It doesn't emit light - it has to be illuminated. When it is you see an illusion of a scene. If we just think about black and white the paints go from black through shades of grey to white. They can't go lighter than white or darker than black. White paint is white, however much light you illuminate it with, and likewise, so is black paint always black.
The output from a digital camera is like a painting, it specifies values in a 'colour space' which correspond to colours of paints (in fact the whole thing was developed for the printing industry). There are a few terms for the characteristic of a paint (or ink) which determines how dark or light it is, but the most descriptive is 'lightness'.
The camera is gathering an amount of light from a scene - not paint colours. We generally talk about amounts of light in terms of 'brightness'. A more technical term is 'luminance', which is converted to 'illuminance' if we're talking about light being shined onto something. So, light coming from a scene is 'luminance', that light, after having been regulated through the aperture gives the 'illuminance' at the focal plane. The illuminance at the focal plane times the time for which it was collected by the sensor is called the exposure.
Techies tend to use lots of words so that they don't muddle them up by using the same word for different things. They also like to have precise and singular meanings for the different words, so they don't end up with equivocation errors. -
Now that's a wilful and deliberate equivocation fallacy.
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Not true at all unless your definition of the word exposure and/or 'scene luminance' is different to what I use.
For example:
Say for a given scene I use:
f/8, 1/200s ISO 100
While reviewing the image I decide it is a little too dark for my liking and the camera histogram shows I have plenty of highlight headroom.
I add more light to the scene and take another shot with the same settings.
This time the image lightness looks how I want and the histogram says I have no highlight clipping.
In this scenario the scene luminance has increased due to the additional light and so the exposure* has increased because more light hit the sensor after the additional light was added.
Therefore your thread title "Scene luminance has nothing to do with exposure." is total BS unless you define 'scene luminance' and 'exposure' as you used them in your title 😃😎
* exposure - amount of light that struck the sensor per unit area while the shutter was open
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They're .... back!
Mean Exposure Hm=0.65Lt/N^2 where L=Scene Luminance ... won't insult y'all with either the other two terms or the constant but ...
... just in case: kronometric.org/phot/lighting/DC-004_EN.pdf
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Thank you.
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But clearly silly photos and gifs in responses are ok, based on many of the posts in this thread so far?
This scene has quite good brightness but I feel that the blacks and shadows could have been lifted a little.
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You are welcome.
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You're trying to create some kind of profundity by oversimplifying things. If you leave a camera set up in time lapse mode, with manual exposure, and the ambient lighting changes over time, then varying "scene luminance" will vary exposure. If you set it up to automate the f-number or exposure time, with a fixed ISO setting, then exposure may be unaffected by scene luminance (except for the granularity of the settings).
Scene luminance may or may not affect exposure; it all depends on the process used in photographing a scene.
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Y'might want to run that by the movie crews who spend a bunch of time and money lighting scenes to control the exposure...
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It must be nice to deliberately post something known to be incorrect and then to bask in the number of responses telling one how wrong one is ...
... is there a particular psychology involved?
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Whether anyone feels blacks or shadows in an image they are viewing on their monitor needs lifting or not will depend to some extent on the brightness the monitor is set to.
A given image viewed on a screen calibrated to 80 cd/m2 might look a little dark compared to it being viewed on a screen calibrated to 190 cd/m2 where it might look OK.
