Luminous Landscape Forum

Raw & Post Processing, Printing => Digital Image Processing => Topic started by: Guillermo Luijk on May 12, 2021, 06:57:02 pm

Title: Unifying colour temperatures of different light sources in RAW
Post by: Guillermo Luijk on May 12, 2021, 06:57:02 pm

Another exercise about synthetic RAW generation. We have a scene with two very different light sources:
- Daylight (we cannot avoid it)
- LED warm light (we cannot change it)

http://guillermoluijk.com/misc/linear2.jpg

(RAW file: http://www.guillermoluijk.com/misc/ambientemasartificial.dng)


We do an extra shot by switching off the LED light so we just get the Daylight:

http://guillermoluijk.com/misc/linear1.jpg

(RAW file: http://www.guillermoluijk.com/misc/soloambiente.dng)


Now by linear subtraction we can isolate the LED light source: LED = (Daylight + LED) - Daylight

The LED RAW data is linearly scaled to mimic the Daylight colour temperature.
A synthetic DNG output file is built by simply adding the Daylight RAW values to the modified LED RAW values:

http://guillermoluijk.com/misc/linear3.jpg

(RAW file: http://guillermoluijk.com/datosimagensonido/rawwhitebalanced.dng)


The output DNG file is RAW in all aspects, but both light sources now have the same colour temperature so a single RAW development will eliminate any colour tint produced by the mismatching original colour temperatures.

Whole exercise: https://www.overfitting.net/2021/05/descomposicion-lineal-de-fuentes-de.html

Regards

Title: Re: Unifying colour temperatures of different light sources in RAW
Post by: glyph on May 12, 2021, 09:17:29 pm

Impressive, to say the least. Science and math for the win! Thanks for sharing.

Title: Re: Unifying colour temperatures of different light sources in RAW
Post by: fdisilvestro on May 13, 2021, 11:42:52 am

Fascinating! Ho do you subtract the two DNG? Is that in your R code?

Title: Re: Unifying colour temperatures of different light sources in RAW
Post by: Guillermo Luijk on May 13, 2021, 05:17:23 pm

Quote from: fdisilvestro on May 13, 2021, 11:42:52 am

Fascinating! Ho do you subtract the two DNG? Is that in your R code?

Sure, all code is available for the four exercises (there is a link to the repo in the end of each article). The RAW subtraction is as simple as:

# LINEAR SUBTRACTION
imag=img[[1]]-img[[2]]  # (Ambiente + Artificial) - Ambiente
imag[imag<0]=0  # clip negative subtractions

An animated GIF showing the before/after colour temperature matching:
(https://1.bp.blogspot.com/-dRVbVDYuXuc/YJ2Slg4knuI/AAAAAAAAKic/BDp574EBud0k94-0zJJxuAzDn_ldRLczQCLcBGAsYHQ/s16000/whitebalanced512.gif)

Regards