Scene luminance has nothing to do with exposure.

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TonyBeach
Members 206 posts

June 18, 2023, 4:55 p.m. June 18, 2023, 4:55 p.m.
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@xpatUSA has written:

@TonyBeach has written:

Tony, could you tell us what ISO was used for the shot and was any Exposure Compensation applied (if so, how much)?

ISO 450

I may have applied EC, though when using Auto-ISO I usually don't. Since it was in Manual Exposure mode I think the EC doesn't show up in the EXIF data (I can't find it here or in a couple of other files I looked at).
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TimoK
Members 300 posts

June 18, 2023, 6:05 p.m. June 18, 2023, 6:05 p.m.
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@TonyBeach has written:

@xpatUSA has written:

@TonyBeach has written:

Tony, could you tell us what ISO was used for the shot and was any Exposure Compensation applied (if so, how much)?

ISO 450

I may have applied EC, though when using Auto-ISO I usually don't. Since it was in Manual Exposure mode I think the EC doesn't show up in the EXIF data (I can't find it here or in a couple of other files I looked at).

In Sony files the EC tag is Exif.Photo.ExposureBiasValue. Exiv2 shows it in form Exif.Photo.ExposureBiasValue SRational 1 -7/10 EV.
EC was -0.7

And Exif.Photo.ExposureBiasValue SRational 1 0 EV in a picture with no exposure correction.

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Deleted Removed user

June 18, 2023, 6:24 p.m. June 18, 2023, 6:24 p.m.
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@TonyBeach has written:

@xpatUSA has written:

@TonyBeach has written:

Tony, could you tell us what ISO was used for the shot and was any Exposure Compensation applied (if so, how much)?

ISO 450

Thanks Tony!

Mystery of "Light Value" solved to my satisfaction ...

LV = EV corrected to ISO100 = log2(N^2/t) - log2(450/100) = 9.34 - 2.17 = 7.17.

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DonaldB
Members 2365 posts

June 18, 2023, 9:52 p.m. June 18, 2023, 9:52 p.m.
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@SrMi has written:

@DonaldB has written:

conclusion: exposure = shutter, t stop, and scene luminance which is displayed by the histogram now we have practical picture (pun) to work off.

The histogram is computed using ISO, WB, etc settings (JPEG), none of them being part of exposure.

the very comprehensive paper i read said that using Auto Wb is used to use a histogram as a luminance meter.
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DonaldB
Members 2365 posts

June 18, 2023, 9:55 p.m. June 18, 2023, 9:55 p.m.
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@JimKasson has written:

@DonaldB has written:

Ok the penny has dropped. and i conceive defeat . well sort of

conclusion: exposure = shutter, t stop, and scene luminance which is displayed by the histogram now we have practical picture (pun) to work off.

come on guys you have dropped the ball explaining the concept to the limited scientific minds. 😎

My fees are cheap if you want to quote my conclusion. 😁

The in camera histogram does not measure scene luminance. It’s affected by other things, too.

www.image-engineering.de/content/library/conference_papers/before_2009/luminance_meters.pdf
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JimKasson
Members 1738 posts

June 18, 2023, 9:58 p.m. June 18, 2023, 9:58 p.m.
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Deleted
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IliahBorg
Members 976 posts

June 18, 2023, 10:03 p.m. June 18, 2023, 10:03 p.m.
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@DonaldB has written:

@SrMi has written:

@DonaldB has written:

conclusion: exposure = shutter, t stop, and scene luminance which is displayed by the histogram now we have practical picture (pun) to work off.

The histogram is computed using ISO, WB, etc settings (JPEG), none of them being part of exposure.

the very comprehensive paper i read said that using Auto Wb is used to use a histogram as a luminance meter.

You misunderstood something. At the very least, the camera needs to be characterized first, to determine the transfer function.

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JACS
Members 878 posts

June 18, 2023, 10:04 p.m. June 18, 2023, 10:04 p.m.
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[deleted]

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JimKasson
Members 1738 posts

June 18, 2023, 10:07 p.m. June 18, 2023, 10:07 p.m.
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@JACS has written:

@DonaldB has written:

@JimKasson has written:

@DonaldB has written:

Ok the penny has dropped. and i conceive defeat . well sort of

conclusion: exposure = shutter, t stop, and scene luminance which is displayed by the histogram now we have practical picture (pun) to work off.

come on guys you have dropped the ball explaining the concept to the limited scientific minds. 😎

My fees are cheap if you want to quote my conclusion. 😁

The in camera histogram does not measure scene luminance. It’s affected by other things, too.

www.image-engineering.de/content/library/conference_papers/before_2009/luminance_meters.pdf

The word "histogram" does not even appear there.

Yup.

image.png
PNG, 32.6 KB, uploaded by JimKasson on June 18, 2023.

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DonaldB
Members 2365 posts

June 18, 2023, 11:23 p.m. June 18, 2023, 11:23 p.m.
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@xpatUSA has written:

@DonaldB has written:

Quote: A histogram is simply a graphic representation of the exposure levels within an image.

Just levels, Donald, not "exposure levels".

the article i read said exposure levels.
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DonaldB
Members 2365 posts

June 18, 2023, 11:27 p.m. June 18, 2023, 11:27 p.m.
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@JimKasson has written:

@JACS has written:

@DonaldB has written:

@JimKasson has written:

@DonaldB has written:

Ok the penny has dropped. and i conceive defeat . well sort of

conclusion: exposure = shutter, t stop, and scene luminance which is displayed by the histogram now we have practical picture (pun) to work off.

come on guys you have dropped the ball explaining the concept to the limited scientific minds. 😎

My fees are cheap if you want to quote my conclusion. 😁

The in camera histogram does not measure scene luminance. It’s affected by other things, too.

www.image-engineering.de/content/library/conference_papers/before_2009/luminance_meters.pdf

The word "histogram" does not even appear there.

Yup.

it was just a good article about luminance. and does contradict many members writings here.
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IliahBorg
Members 976 posts

June 18, 2023, 11:36 p.m. June 18, 2023, 11:36 p.m.
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@DonaldB has written:

it was just a good article about luminance.

But you need to understand it.

@DonaldB has written:

and does contradict many members writings here.

As I said, you misunderstood the article.
Feel free to ask questions.

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IliahBorg
Members 976 posts

June 18, 2023, 11:40 p.m. June 18, 2023, 11:40 p.m.
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@DonaldB has written:

@xpatUSA has written:

@DonaldB has written:

Quote: A histogram is simply a graphic representation of the exposure levels within an image.

Just levels, Donald, not "exposure levels".

the article i read said exposure levels.

Which article?
Which histogram?
What is exposure level?

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JimKasson
Members 1738 posts

June 18, 2023, 11:58 p.m. June 18, 2023, 11:58 p.m.
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@DonaldB has written:

it was just a good article about luminance. and does contradict many members writings here.

Not sure what you're talking about. Be explicit about the contradictions that you see. List them.

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Deleted Removed user

June 19, 2023, 2:08 a.m. June 19, 2023, 2:08 a.m.
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@DonaldB has written:

@xpatUSA has written:

@DonaldB has written:

Quote: A histogram is simply a graphic representation of the exposure levels within an image.

Just levels, Donald, not "exposure levels".

the article i read said exposure levels.

This one? (not a trap)

capturetheatlas.com/how-to-read-a-histogram-in-photography/
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DonaldB
Members 2365 posts

June 19, 2023, 4 a.m. June 19, 2023, 4 a.m.
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@IliahBorg has written:

@DonaldB has written:

@xpatUSA has written:

@DonaldB has written:

Quote: A histogram is simply a graphic representation of the exposure levels within an image.

Just levels, Donald, not "exposure levels".

the article i read said exposure levels.

Which article?
Which histogram?
What is exposure level?

artschoolportal.com/2016/11/light-meters-exposure/
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DonaldB
Members 2365 posts

June 19, 2023, 4:02 a.m. June 19, 2023, 4:02 a.m.
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@xpatUSA has written:

@DonaldB has written:

@xpatUSA has written:

@DonaldB has written:

Quote: A histogram is simply a graphic representation of the exposure levels within an image.

Just levels, Donald, not "exposure levels".

the article i read said exposure levels.

This one? (not a trap)

capturetheatlas.com/how-to-read-a-histogram-in-photography/

no but it says the same as this one.

artschoolportal.com/2016/11/light-meters-exposure/
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TimoK
Members 300 posts

June 19, 2023, 4:30 a.m. June 19, 2023, 4:30 a.m.
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@DonaldB has written:

@IliahBorg has written:

@DonaldB has written:

@xpatUSA has written:

@DonaldB has written:

Quote: A histogram is simply a graphic representation of the exposure levels within an image.

Just levels, Donald, not "exposure levels".

the article i read said exposure levels.

Which article?
Which histogram?
What is exposure level?

artschoolportal.com/2016/11/light-meters-exposure/

I don't find "Exposure levels" there.