EXIF Brightness Value (what is it)

Started Jul 28, 2008 | Discussions
Brian Salyer Senior Member • Posts: 1,096
EXIF Brightness Value (what is it)

Hello,

I have searched and have not found anthing that explains what the "brightness value" in the exif information is on an S5 file.

I recently shot a wedding Saturday. We did all the formal shots with two monolights set to meter F8 at 125 ISO400. Set the camera to the same settings in manual mode. Did a custom white balance and we were off to the races. No exposure comp.

I shot in F1 mode with a +1 on sharpness and +1 on color.

I shot jpg large fine + raw.

The images looked great on the lcd and the histogram looked right on the money.

Upon opening them up after the wedding. The images are a touch on the dark side. An auto level in photoshop brightens them right up and of course I have the raw files to work with.

However the exif data shows a -1..... in the brightness value.
I have no idea what this is or if any camera settings affect it.

Any thoughts would be greatly appreciated.

Regards,

Brian

ej64 Regular Member • Posts: 226
It's the average scene luminance

It's an ASA standardized brightness value of the avarage scene luminance. It is used within the APEX system.

Have you ever bothered using wikipedia?
http://en.wikipedia.org/wiki/APEX_system
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DiDo Regular Member • Posts: 346
Re: EXIF Brightness Value (what is it)

not really sure about it. i made a control with a photo of the following parameters:

ISO Speed 200, f-stop 6.7, shutter speed 4.5 sec. the S5-Brightness is -2.5. the correct result with the formula in the tutorial is 9.4. What isi wrong??

ej64 Regular Member • Posts: 226
no, your Fuji is right

read the above posted wiki-link.

Bv = log2 (A² T/Sx/N)

A= Aperture, here 6.7
T= Time in s
Sx= ISO speed
N= konst. ~ 0.30

=> Bv = log2 (6.7² 4.5/200/0.3) = log2 (0.166) = -2.588

For you can't compute a base 2 logarithm on most calculators, you can use a simple base change:

log2 (0.166) = ( log (0.166) ) / ( log (2) )
--
best regards
Eberhard
my site: http://www.ej64.de -- galleries, blog (german) and other stuff

Mike Wee Contributing Member • Posts: 662
Re: It's the average scene luminance

ej64 wrote:

It's an ASA standardized brightness value of the avarage scene luminance. It is used within the APEX system.

Eberhard,

Do you know if this is the sensor-measured value or the calculated value from shooting parameters?

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ShortCipher New Member • Posts: 8
Re: no, your Fuji is right

There's a typo in ej64's example.

6.7² 4.5/200/0.3 = 3.366

It should be

6.7² /4.5/200/0.3 = 0.166

nixda Veteran Member • Posts: 5,515
Re: no, your Fuji is right
1

ShortCipher wrote:

There's a typo in ej64's example.

6.7² 4.5/200/0.3 = 3.366

It should be

6.7² /4.5/200/0.3 = 0.166

Haha, this might be a record for resurrecting the oldest thread.

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Vic Chapman Forum Pro • Posts: 10,694
Re: no, your Fuji is right

ShortCipher wrote:

There's a typo in ej64's example.

6.7² 4.5/200/0.3 = 3.366

It should be

6.7² /4.5/200/0.3 = 0.166

Trying to correct the calculation after 9 years have passed is bad enough - but to incorrectly correct it is even worse - where is this phantom 3.366 you mention?

Vic

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nixda Veteran Member • Posts: 5,515
Re: no, your Fuji is right
1

Vic Chapman wrote:

ShortCipher wrote:

There's a typo in ej64's example.

6.7² 4.5/200/0.3 = 3.366

It should be

6.7² /4.5/200/0.3 = 0.166

Trying to correct the calculation after 9 years have passed is bad enough - but to incorrectly correct it is even worse - where is this phantom 3.366 you mention?

No, no, he is right. The way it reads in ej64's post is:

6.7^2*4.5/200/0.3

and that gives 3.367

But it should be 6.7^2/4.5/200/0.3, which gives 0.166

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Vic Chapman Forum Pro • Posts: 10,694
Re: no, your Fuji is right

nixda wrote:

Vic Chapman wrote:

ShortCipher wrote:

There's a typo in ej64's example.

6.7² 4.5/200/0.3 = 3.366

It should be

6.7² /4.5/200/0.3 = 0.166

Trying to correct the calculation after 9 years have passed is bad enough - but to incorrectly correct it is even worse - where is this phantom 3.366 you mention?

No, no, he is right. The way it reads in ej64's post is:

6.7^2*4.5/200/0.3

and that gives 3.367

But it should be 6.7^2/4.5/200/0.3, which gives 0.166

I'll take your word for it. It's all double Dutch to me. I missed 2 years schooling through ill health (13/14) and was in full time work at 15.

Vic

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