What is 'brightnessValue' (formatted metadata)?

[areohbee]

From API doc:

* aperture: (string) The aperture (for example, "f/2.8")

* brightnessValue: (string) The brightness value (HELP: need an example)

* exposureBias: (string) The exposure bias/compensation (for example, "-2/3 EV")

I could use an example too, and/or an explanation.

Anybody?

Thanks,

Rob

[johnrellis · Accepted solution]

I believe that photo:getFormattedMetadata ("brightnessValue") is the APEX average scene luminance recorded in the EXIF metadata:

http://en.wikipedia.org/wiki/APEX_system#Use_of_APEX_values_in_Exif

According to the EXIF spec:

I don't really understand any of the details.

[DawMatt]

Rob Cole wrote:

* brightnessValue: (string) The brightness value (HELP: need an example)

...

I could use an example too, and/or an explanation.

I suspect brightness value isn't really used by Lightroom any more. This is why the tech writer didn't have an example to include for this field.

I have checked a number of images (NEF, JPEG, DNG) from different camera types using a metadata tagset including the com.adobe.brightnessValue field. Not one of the sample images displayed a value under Lightroom 4. These same images when checked in exiftool had a "Brighness Value" of "Normal".

Opening up LR 2.7 I managed to find one sample image in that catalog with a brightness value. The metadata tagset field com.adobe.brightnessValue displayed a value of 4.96. This seems to align with the doco John managed to find.

I'd suggest ignoring the field. But I will see if the doco can be updated.

[areohbee]

Thanks John, and Matt .

(Rob)

[johnrellis]

In a catalog of 20K photos from perhaps a dozen different cameras, I found just 150 photos with non-empty Brightness Value fields, mostly from my new Sony RX100, which seems to always insert the field.  Skimming the values, they appear to range from about -3 to +7.