Photography

Color Temperature Measured

 

When your digital camera is set to AWB there are (at least) three metrics in play: color temperature as measured in Kelvin (K), the light balance (LB) measured as "mired units" (micro reciprocal degree), and color-compensation (CC).  LB is a reference to the amber/blue balance while CC refers to the red(magenta)/green compensation.  Color temperature meters are also able to provide reference light measurements for the photographer.  How you use that information is up to you.

Recently I acquired a Kenko KCM-3100 Color Meter.  I was looking at the Sekonic Spectromaster C-700 as in addition to the three metrics discussed above it is able to provide a CRI (Color Rendering Index) reference, particularly individual spectrum issues... alas my budget is limited.

Over the last few weeks I have been testing the color meter, initially as a reference when doing digital photography... I would like to share a few initial thoughts.

Canon 5D Mk II using AWB

As shot and recorded in the exif data the WB RGB Levels were: 2040 1024 2194 with a Color Temp of: 4078 K.  When I measured with the color meter the light falling on the scene it gave a measurement of 4180 K.  So I shot another photo with the WB fixed at 4200 K as follows.

Canon 5D Mk II using WB at 4200 K

As you may be able to see, the rendering of the latter photo with a fixed Kelvin setting is slightly off.  In fact the LB seems to improved to my eye, but the red (magenta) / green mix could stand some adjustment.  This is because setting the color temperature only addresses one of the three metrics.

Typical measurement (Color Temperature in Kelvin)




Typical measurement (LB & CC)

The color meter that I have can be used for film or digital, while the LB and CC shown are as if I am using daylight color film (i.e. film / sensor balanced for 5500 K).  In my experience the LB reference is linked to the color temperature while the CC reference can be treated as a stand alone metric.

For testing, my approach is to set the digital camera to the color temperature as measured by the color meter and adjust the red / green mix in post based in the measured CC data.  For example using the measurements show above, I would set the color temperature to 2810 K and add some red (magenta) in processing.  If shooting RAW both the WB Kelvin setting and CC (red / green) mix can be done while processing the file.

Conclusion: using measurement tools and exif data it's interesting to already see how much and where the mfgs compensate / adjust the digital imaging process...  it's early days of testing and quantifying the process can introduce additional problems into the workflow...  it's an on going process as usual.

Casey