White balance offset (for IR work)

[szgabor (Gabor)]

@ilias_giarimis

This matrix is either hardoded in dcraw (RT’s decoding engine) or defined in camconst.json so to give you freedom regarding temp/tint manipulations I “calculated” (it’s a guess work in fact …) one. Insert the following lines in your camconst.json file.

Thank you very much, it has solved the problem - at least for the G9. Unfortunately it doesn’t work with the A480 (DNG v1.3 RAWs, generated by the firmware hack CHDK, as this cheap cam doesn’t natively support RAW)

The end of my camconst.json now reads:

    { //   Quality X, experimental infrared support
        "make_model": "Canon PowerShot G9",
    //  "dcraw_matrix": [ 7368,-2141,-598,-5621,13254,2625,-1419,1696,5743 ], // DNG_V8.7 D65
        "dcraw_matrix": [ 15613,-6767,-2468,-1924,5307,221,323,-200,2196 ], // Infrared guessed
        "ranges": { "white": 4080 }
    },
    
    { //   Quality X, experimental infrared support
        "make_model": "Canon PowerShot A480",
    //  "dcraw_matrix": [ 7368,-2141,-598,-5621,13254,2625,-1419,1696,5743 ], // DNG_V8.7 D65
        "dcraw_matrix": [ 15613,-6767,-2468,-1924,5307,221,323,-200,2196 ], // Infrared guessed
        "ranges": { "white": 4080 }
    }
    
]}

A RAW sample has been posted already in this topic.

(well maybe we could calculate a better matrix if we had a cc24 shot under IR …)

I can indeed shoot it, but only the grayscale row can be hoped to behave as intended in IR - depending on the colorants used. The other fields will just look “somehow”, as they haven’t been designed to look a particular way in IR. I guess most will look pretty whitish, as most dyes are transparent in IR, while some deep green and blue colored ones will be bluish, as these absorb the upper 60nm band transmitted by the filter responsible for all the more red colors. However, if you need samples of the extremes of colors to handle, I can produce them using LEDs.