Can activate DCP tonecurve although there is none

Andi · January 25, 2020, 5:41pm

I use the Adobe Standard profile for Nikon D5200 ( Nikon D5200 Adobe Standard.dcp (117.9 KB) or as JSON: Nikon D5200 Adobe Standard.json.dcp (1.1 MB) )

In the JSON file you see that there is no tonecurve included. It seems that it is somehow encoded into to the HueSatMap. How can Lightroom and RawTherapee know this? I can (de)activate the tone curve under “Input Profile”. Other profiles I created with DCamProf without a tone curve behave as expected: the “tone curve” checkbox is grayed out.

Andi · January 25, 2020, 6:04pm

Answer for Lightroom (5.5):

dcamprof make-dcp ... -t none includes a linear tonecurve into the DCP (which only includes 0 => 0, 1 => 1). This lets Lightroom deactivate the tonecurve, if the “ProfileToneCurve” is missing, else Lightroom applies a default tonecurve.

But this does not answer my question for RawTherapee (5.6).

The_Squirrel_Mafia · January 26, 2020, 6:51am

I’m not sure how that works, but I’d completely skip that generic DCP file.

https://helpx.adobe.com/photoshop/using/adobe-dng-converter.html#DownloadtheDNGConverter

^ Download that & then go to the Nikon D5200 folder to get the Landscape, Neutral, Portrait, Standard, & Vivid DCP files.

https://rawpedia.rawtherapee.com/How_to_get_LCP_and_DCP_profiles

^ More info there. You can extract them using 7-zip or something.

agriggio · January 26, 2020, 7:43am

if it’s an Adobe profile (detected by copyright info), RT applies a default “film curve”, to match what lightroom does (disclaimer: I’ve never used lightroom, and I am just going from memory of the DCP code in RT)

Morgan_Hardwood · January 26, 2020, 10:52am

Hi @agriggio, could you point me to the relevant code, so that I can update the docs?

agriggio · January 26, 2020, 1:08pm

github.com

Beep6581/RawTherapee/blob/24684e5cb35a2d487cc74407941b795788566a9f/rtengine/dcp.cc#L949

    
      
              }
          
          
    if (!curve_is_linear) {
                  // Create the curve
                  has_tone_curve = true;
                  tone_curve.Set(DiagonalCurve(curve_points, CURVES_MIN_POLY_POINTS));
              }
          } else {
              tag = tagDir->getTag(toUnderlying(TagKey::PROFILE_TONE_COPYRIGHT));
          
          
    if (tag && tag->valueToString().find("Adobe Systems") != std::string::npos) {
                  // An Adobe profile without tone curve is expected to have the Adobe Default Curve, we add that
                  std::vector<double> curve_points = {
                      static_cast<double>(DCT_Spline)
                  };
          
          
        constexpr size_t tc_len = sizeof(adobe_camera_raw_default_curve) / sizeof(adobe_camera_raw_default_curve[0]);
          
          
        for (size_t i = 0; i < tc_len; ++i) {
                      const double x = static_cast<double>(i) / (tc_len - 1);
                      const double y = adobe_camera_raw_default_curve[i];

Morgan_Hardwood · January 27, 2020, 12:57pm

Thank you.

Morgan_Hardwood · January 27, 2020, 1:24pm

Docs updated:
http://rawpedia.rawtherapee.com/Color_Management#DCP_Tone_Curve