raw: fix ProPhoto gamma, add ProPoto-linear (#3153)

When requesting that raw image be returned as "ProPhoto" color space, we were using the wrong gamma. Also, at user request, add "ProPhoto-linear", which is the same but with linear response. (This is analogous to the existing "sRGB" and "sRGB-linear".) Fixes #3152
AcademySoftwareFoundation · Oct 28, 2021 · fa26dab · fa26dab
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diff --git a/src/doc/builtinplugins.rst b/src/doc/builtinplugins.rst
@@ -1514,9 +1514,9 @@ options are supported:
      - string
      - Which color primaries to use for the returned pixel values: ``raw``,
        ``sRGB``, ``sRGB-linear`` (sRGB primaries, but a linear transfer
-       function), ``Adobe``, ``Wide``, ``ProPhoto``, ``XYZ``, ``ACES`` (only
-       supported by LibRaw >= 0.18), ``DCI-P3`` (LibRaw >= 0.21), ``Rec2020``
-       (LibRaw >= 0.2). (Default: ``sRGB``)
+       function), ``Adobe``, ``Wide``, ``ProPhoto``, ``ProPhoto-linear``,
+       ``XYZ``, ``ACES`` (only supported by LibRaw >= 0.18), ``DCI-P3``
+       (LibRaw >= 0.21), ``Rec2020`` (LibRaw >= 0.2). (Default: ``sRGB``)
    * - ``raw:Exposure``
      - float
      - Amount of exposure before de-mosaicing, from 0.25 (2 stop darken) to

diff --git a/src/raw.imageio/rawinput.cpp b/src/raw.imageio/rawinput.cpp
@@ -542,6 +542,12 @@ RawInput::open_raw(bool unpack, const std::string& name,
         m_processor->imgdata.params.output_color = 1;
         m_processor->imgdata.params.gamm[0]      = 1.0 / 2.4;
         m_processor->imgdata.params.gamm[1]      = 12.92;
+    } else if (Strutil::iequals(cs, "sRGB-linear")
+               || Strutil::iequals(cs, "linear") /* DEPRECATED */) {
+        // Request "sRGB" primaries, linear reponse
+        m_processor->imgdata.params.output_color = 1;
+        m_processor->imgdata.params.gamm[0]      = 1.0;
+        m_processor->imgdata.params.gamm[1]      = 1.0;
     } else if (Strutil::iequals(cs, "Adobe")) {
         // Request Adobe color space with 2.2 gamma (no linear toe)
         m_processor->imgdata.params.output_color = 2;
@@ -554,8 +560,13 @@ RawInput::open_raw(bool unpack, const std::string& name,
     } else if (Strutil::iequals(cs, "ProPhoto")) {
         // ProPhoto by convention has gamma 1.8
         m_processor->imgdata.params.output_color = 4;
-        m_processor->imgdata.params.gamm[0]      = 1.8;
+        m_processor->imgdata.params.gamm[0]      = 1.0 / 1.8;
         m_processor->imgdata.params.gamm[1]      = 0.0;
+    } else if (Strutil::iequals(cs, "ProPhoto-linear")) {
+        // Linear version of PhotoPro
+        m_processor->imgdata.params.output_color = 4;
+        m_processor->imgdata.params.gamm[0]      = 1.0;
+        m_processor->imgdata.params.gamm[1]      = 1.0;
     } else if (Strutil::iequals(cs, "XYZ")) {
         // XYZ linear
         m_processor->imgdata.params.output_color = 5;
@@ -594,12 +605,6 @@ RawInput::open_raw(bool unpack, const std::string& name,
                  cs, LIBRAW_VERSION_STR);
         return false;
 #endif
-    } else if (Strutil::iequals(cs, "sRGB-linear")
-               || Strutil::iequals(cs, "linear") /* DEPRECATED */) {
-        // Request "sRGB" primaries, linear reponse
-        m_processor->imgdata.params.output_color = 1;
-        m_processor->imgdata.params.gamm[0]      = 1.0;
-        m_processor->imgdata.params.gamm[1]      = 1.0;
     } else {
         errorf("raw:ColorSpace set to unknown value \"%s\"", cs);
         return false;