what are derived d65 multipliers?

Submitted by laserpanda on

with raw-identify -v i get:

Derived D65 multipliers: 2.172879 0.947545 1.527648

but i can also see:

Makernotes 'D65' WB multipliers: 654 302 488 302

why isnt the relative difference between the channels equal?

thanks

Forums: 

Derived D65 multipliers are

Submitted by lexa on

Derived D65 multipliers are calculated from daylight color profile, while makernotes multipliers are recorded by camera.

-- Alex Tutubalin @LibRaw LLC

So when you say daylight

Submitted by laserpanda on

So when you say daylight colour profile, its a preset that comes with libraw vs what the camera thinks it should be? is there any reason the derived values should be more correct than the makernote values?

Unless your scene is lit by

Submitted by lexa on

Unless your scene is lit by exact D65 (imaginary) light source, both values are 'not correct'

-- Alex Tutubalin @LibRaw LLC

Your question is 'is there

Submitted by lexa on

Your question is 'is there any reason the derived values should be more correct....'
My question is: 'more correct for WHAT?'

Real scene is lit by some real (daylight) light source, not (imaginary/synthetic) black body at 6500K.
Both settings are 'not correct' for real image/real scene.

-- Alex Tutubalin @LibRaw LLC

the question was a two-parter

Submitted by laserpanda on

the question was a two-parter.

first: "So when you say daylight colour profile, its a preset that comes with libraw vs what the camera thinks it should be?"

Second, if there is no way to correctly white balance to 6500k, then why do we even have these numbers to begin with?

There are other reasons for wanting to get a correct d6500 white balance than matching a physical lamp. For example if i have to work with raw files from several cameras: then if they could all reliably be set to a 6500k white balance, they would at least all match eachother regardless of the actual lamp temperature, saving one self the work of having to grade each camera individually.

Also look at the rawtoaces project. it is specifically made to convert raw files to aces colourspace which is calibrated around a 6000k (?) whitepoint. Unfortunately not all cameras have had their sensors analysed for spectral sensitivity.

LibRaw allows to set any

Submitted by lexa on

LibRaw allows to set any white balance, including the ones that comes from camera metadata (use imgdata.params.user_mul[] for that).

-- Alex Tutubalin @LibRaw LLC