feat: Support display color space interop IDs in I/O

Previously only srgb_rec709_scene was recognized as sRGB for file metadata
and display, now srgb_rec709_display and g22_rec709_display are treated
as sRGB as well.

The reason for g22_rec709_display behavior is that this type of display is
often used to correct for the discrepancy where images are encoded as sRGB but
usually decoded as gamma 2.2 by the physical display. By encoding it as gamma
2.2 and claiming it's sRGB the transfer functions cancel out exactly.

g24_rec709_display is now recognized as having gamma 2.4, and
g24_rec709_scene was replaced by ocio:g24_rec709_scene since the
former is not an official interop ID.

ocio:itu709_rec709_scene and ocio:lin_ciexyzd65_display to complete
the list of interop IDs in OCIO configs that match a CICP.

None of the other display color space interop IDs required changes.

Signed-off-by: Brecht Van Lommel <brecht@blender.org>

Author: brechtvl

src/libOpenImageIO/color_ocio.cpp

@@ -2087,6 +2087,9 @@ constexpr ColorInteropID color_interop_ids[] = {
     // Display referred interop IDs.
     { "srgb_rec709_display", CICPPrimaries::Rec709, CICPTransfer::sRGB,
       CICPMatrix::BT709 },
+    // Not all software interprets this CICP the same, see the
+    // "QuickTime Gamma Shift" issue. We follow the CIF recommendation and
+    // interpret it as BT.1886.
     { "g24_rec709_display", CICPPrimaries::Rec709, CICPTransfer::BT709,
       CICPMatrix::BT709 },
     { "srgb_p3d65_display", CICPPrimaries::P3D65, CICPTransfer::sRGB,
@@ -2099,11 +2102,13 @@ constexpr ColorInteropID color_interop_ids[] = {
       CICPMatrix::Rec2020_NCL },
     { "hlg_rec2020_display", CICPPrimaries::Rec2020, CICPTransfer::HLG,
       CICPMatrix::Rec2020_NCL },
-    // No CICP mapping to keep previous behavior unchanged, as Gamma 2.2
-    // display is more likely meant to be written as sRGB. On read the
-    // scene referred interop ID will be used.
-    { "g22_rec709_display",
-      /* CICPPrimaries::Rec709, CICPTransfer::Gamma22, CICPMatrix::BT709 */ },
+    // Mapped to sRGB as a gamma 2.2 display is more likely meant to be written
+    // as sRGB. This type of display is often used to correct for the discrepancy
+    // where images are encoded as sRGB but usually decoded as gamma 2.2 by the
+    // physical display.
+    // For read and write, g22_rec709_scene. still maps to Gamma 2.2.
+    { "g22_rec709_display", CICPPrimaries::Rec709, CICPTransfer::sRGB,
+      CICPMatrix::BT709 },
     // No CICP code for Adobe RGB primaries.
     { "g22_adobergb_display" },
     { "g26_p3d65_display", CICPPrimaries::P3D65, CICPTransfer::Gamma26,
@@ -2112,6 +2117,15 @@ constexpr ColorInteropID color_interop_ids[] = {
       CICPMatrix::Unspecified },
     { "pq_xyzd65_display", CICPPrimaries::XYZD65, CICPTransfer::PQ,
       CICPMatrix::Unspecified },
+
+    // OpenColorIO interop IDs.
+    { "ocio:g24_rec709_scene", CICPPrimaries::Rec709, CICPTransfer::BT709,
+      CICPMatrix::BT709 },
+    // Not mapped to any CICP, because we already interpret the potential CICP
+    // as g24_rec709_*, see explanation for g24_rec709_display above.
+    { "ocio:itu709_rec709_scene" },
+    { "ocio:lin_ciexyzd65_display", CICPPrimaries::XYZD65, CICPTransfer::Linear,
+      CICPMatrix::Unspecified }
 };
 }  // namespace
 
@@ -2813,7 +2827,7 @@ ColorConfig::set_colorspace_rec709_gamma(ImageSpec& spec, float gamma) const
         set_colorspace(spec, "g22_rec709_scene");
         spec.attribute("oiio:Gamma", 2.2f);
     } else if (fabsf(gamma - 2.4f) <= 0.01f) {
-        set_colorspace(spec, "g24_rec709_scene");
+        set_colorspace(spec, "ocio:g24_rec709_scene");
         spec.attribute("oiio:Gamma", 2.4f);
     } else {
         set_colorspace(spec, Strutil::fmt::format("g{}_rec709_scene",
@@ -2849,7 +2863,11 @@ pvt::is_colorspace_srgb(const ImageSpec& spec, bool default_to_srgb)
 
     const ColorConfig& colorconfig(ColorConfig::default_colorconfig());
     string_view interop_id = colorconfig.get_color_interop_id(colorspace);
-    return interop_id == "srgb_rec709_scene";
+
+    // See the interop table above for why g22_rec709_display is treated as sRGB
+    return (interop_id == "srgb_rec709_scene"
+            || interop_id == "srgb_rec709_display"
+            || interop_id == "g22_rec709_display");
 }
 
 float
@@ -2864,11 +2882,13 @@ pvt::get_colorspace_rec709_gamma(const ImageSpec& spec)
         || colorconfig.equivalent(colorspace, "scene_linear")
         || interop_id == "lin_rec709_scene")
         return 1.0f;
+    // See the interop table above for why g22_rec709_display is not treated as gamma
     else if (interop_id == "g22_rec709_scene")
         return 2.2f;
-    // Note g24_rec709_scene is not a standard interop ID
-    else if (colorconfig.equivalent(colorspace, "g24_rec709_scene"))
+    else if (interop_id == "ocio:g24_rec709_scene"
+             || interop_id == "g24_rec709_display")
         return 2.4f;
+    // Note g18_rec709_display is not an interop ID
     else if (interop_id == "g18_rec709_scene")
         return 1.8f;
     // Back compatible, this is DEPRECATED(3.1)

src/raw.imageio/rawinput.cpp

@@ -577,6 +577,7 @@ RawInput::open_raw(bool unpack, bool process, const std::string& name,
         m_processor->imgdata.params.gamm[0]      = 1.0;
         m_processor->imgdata.params.gamm[1]      = 1.0;
     } else if (colorconfig.equivalent(cs, "srgb_rec709_scene")
+               || colorconfig.equivalent(cs, "srgb_rec709_display")
                || Strutil::iequals(cs, "sRGB") /* Necessary? */) {
         // Request explicit sRGB, including usual sRGB response
         m_processor->imgdata.params.output_color = 1;

testsuite/png/ref/out-libpng15.txt

@@ -102,5 +102,16 @@ remove_cicp_via_set_colorspace:
   16 x   16, 4 channel, float png
     channel list: R, G, B, A
     oiio:ColorSpace: "g22_rec709_display"
+Reading g22_rec709_display.png
+g22_rec709_display.png :   64 x   64, 3 channel, uint8 png
+    SHA-1: 7CB41FEA50720B48BE0C145E1473982B23E9AB77
+    channel list: R, G, B
+    oiio:ColorSpace: "g22_rec709_display"
+Reading g22_rec709_scene.png
+g22_rec709_scene.png :   64 x   64, 3 channel, uint8 png
+    SHA-1: 7CB41FEA50720B48BE0C145E1473982B23E9AB77
+    channel list: R, G, B
+    oiio:ColorSpace: "g22_rec709_scene"
+    oiio:Gamma: 2.2
 Comparing "test16.png" and "ref/test16.png"
 PASS

testsuite/png/ref/out.txt

@@ -103,5 +103,16 @@ remove_cicp_via_set_colorspace:
   16 x   16, 4 channel, float png
     channel list: R, G, B, A
     oiio:ColorSpace: "g22_rec709_display"
+Reading g22_rec709_display.png
+g22_rec709_display.png :   64 x   64, 3 channel, uint8 png
+    SHA-1: 7CB41FEA50720B48BE0C145E1473982B23E9AB77
+    channel list: R, G, B
+    oiio:ColorSpace: "g22_rec709_display"
+Reading g22_rec709_scene.png
+g22_rec709_scene.png :   64 x   64, 3 channel, uint8 png
+    SHA-1: 7CB41FEA50720B48BE0C145E1473982B23E9AB77
+    channel list: R, G, B
+    oiio:ColorSpace: "g22_rec709_scene"
+    oiio:Gamma: 2.2
 Comparing "test16.png" and "ref/test16.png"
 PASS

testsuite/png/run.py

@@ -43,4 +43,10 @@
 # Test that "set_colorspace" removes CICP metadata
 command += oiiotool ("-echo remove_cicp_via_set_colorspace: test16.png --eraseattrib Software --cicp 1,13 --iscolorspace g22_rec709_display --printinfo")
 
+# Test g22_rec709_display being written as sRGB
+command += oiiotool ("--create 64x64 3 --iscolorspace g22_rec709_display -o g22_rec709_display.png")
+command += oiiotool ("--create 64x64 3 --iscolorspace g22_rec709_scene -o g22_rec709_scene.png")
+command += info_command ("g22_rec709_display.png", safematch=True)
+command += info_command ("g22_rec709_scene.png", safematch=True)
+
 outputs = [ "test16.png", "out.txt" ]