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

* Display referred interop IDs are now chosen over scene referred ones by
  default on file read. This more closely matches the standards for CICP, ICC
  and other color metadata. Most images will now have oiio:ColorSpace set to
  srgb_rec709_display rather than srgb_rec709_scene on file read.

  There is groundwork to add control to prefer either display or scene
  referred, but I'm not sure yet what the best way to expose it is.

* Both srgb_rec709_scene and srgb_rec709_display are now (distinct) built-in
  color spaces. The built-in "sRGB" color space name was changed to be an alias
  of srgb_rec709_display rather than srgb_rec709_scene.

* 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 the name
  g24_rec709_scene was replaced with ocio:g24_rec709_scene since the
  former is not an official interop ID.

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

Signed-off-by: Brecht Van Lommel <[email protected]>

Author: brechtvl

src/bmp.imageio/bmpinput.cpp

@@ -8,6 +8,8 @@
 #include <OpenImageIO/fmath.h>
 #include <OpenImageIO/imageio.h>
 
+#include "imageio_pvt.h"
+
 #include "bmp_pvt.h"
 
 OIIO_PLUGIN_NAMESPACE_BEGIN
@@ -262,7 +264,8 @@ BmpInput::open(const std::string& name, ImageSpec& newspec,
     // Default presumption is that a BMP file is meant to look reasonable on a
     // display, so assume it's sRGB. This is not really correct -- see the
     // comments below.
-    m_spec.attribute("oiio:ColorSpace", "srgb_rec709_scene");
+    const bool erase_other_attributes = false;
+    pvt::set_colorspace_srgb(m_spec, erase_other_attributes);
 #if 0
     if (m_dib_header.size >= WINDOWS_V4
         && m_dib_header.cs_type == CSType::CalibratedRGB) {

src/dds.imageio/ddsinput.cpp

@@ -15,6 +15,8 @@
 #include <OpenImageIO/parallel.h>
 #include <OpenImageIO/typedesc.h>
 
+#include "imageio_pvt.h"
+
 #include "dds_pvt.h"
 #define BCDEC_IMPLEMENTATION
 #include "bcdec.h"
@@ -828,7 +830,7 @@ DDSInput::seek_subimage(int subimage, int miplevel)
     if (bpp != 0)
         m_spec.attribute("oiio:BitsPerSample", bpp);
 
-    const char* colorspace = nullptr;
+    bool is_srgb = false;
 
     if (m_dds.fmt.fourCC == DDS_4CC_DX10) {
         switch (m_dx10.dxgiFormat) {
@@ -838,18 +840,17 @@ DDSInput::seek_subimage(int subimage, int miplevel)
         case DDS_FORMAT_BC7_UNORM_SRGB:
         case DDS_FORMAT_R8G8B8A8_UNORM_SRGB:
         case DDS_FORMAT_B8G8R8A8_UNORM_SRGB:
-        case DDS_FORMAT_B8G8R8X8_UNORM_SRGB:
-            colorspace = "srgb_rec709_scene";
-            break;
+        case DDS_FORMAT_B8G8R8X8_UNORM_SRGB: is_srgb = true; break;
         }
     }
 
-    // linear color space for HDR-ish images
-    if (colorspace == nullptr
-        && (basetype == TypeDesc::HALF || basetype == TypeDesc::FLOAT))
-        colorspace = "lin_rec709_scene";
-
-    m_spec.set_colorspace(colorspace);
+    if (is_srgb) {
+        pvt::set_colorspace_srgb(m_spec);
+    } else if (!is_srgb
+               && (basetype == TypeDesc::HALF || basetype == TypeDesc::FLOAT)) {
+        // linear color space for HDR-ish images
+        m_spec.set_colorspace("lin_rec709_scene");
+    }
 
     m_spec.default_channel_names();
     // Special case: if a 2-channel DDS RG or YA?

src/doc/stdmetadata.rst

@@ -149,9 +149,11 @@ Color information
     - `"lin_ap1_scene"`, `"ACEScg"` :  ACEScg color space encoding.
     - `"lin_ap0_scene"` :  ACES2065-1, the recommended ACES space for
       interchange and archiving.
-    - `"srgb_rec709_scene"` : Using standard (piecewise) sRGB response and
+    - `"srgb_rec709_display"` : Using standard (piecewise) sRGB response and
       primaries. The token `"sRGB"` is treated as a synonym.
-    - `"g22_rec709_scene"` : Rec709/sRGB primaries, but using a response curve
+    - `"srgb_rec709_scene"` : Same response and primaries as
+      `"srgb_rec709_display"` but for scene referred images.
+    - `"g22_rec709_display"` : Rec709/sRGB primaries, but using a response curve
       corresponding to gamma 2.2.
 
     Additionally, `"scene_linear"` is a role that is appropriate for color

src/dpx.imageio/dpxinput.cpp

@@ -21,6 +21,7 @@
 // ago and are probably the sole maintainers of this code, and just allow
 // ourselves to diverge from the original.
 
+#include "imageio_pvt.h"
 #include "libdpx/DPX.h"
 #include "libdpx/DPXColorConverter.h"
 #include "libdpx/DPXHeader.h"
@@ -314,7 +315,7 @@ DPXInput::seek_subimage(int subimage, int miplevel)
     switch (m_dpx.header.Transfer(subimage)) {
     case dpx::kLinear: m_spec.set_colorspace("lin_rec709_scene"); break;
     case dpx::kLogarithmic: m_spec.set_colorspace("KodakLog"); break;
-    case dpx::kITUR709: m_spec.set_colorspace("srgb_rec709_scene"); break;
+    case dpx::kITUR709: pvt::set_colorspace_srgb(m_spec); break;
     case dpx::kUserDefined:
         if (!std::isnan(m_dpx.header.Gamma()) && m_dpx.header.Gamma() != 0) {
             set_colorspace_rec709_gamma(m_spec, float(m_dpx.header.Gamma()));

src/ffmpeg.imageio/ffmpeginput.cpp

@@ -71,6 +71,7 @@ receive_frame(AVCodecContext* avctx, AVFrame* picture, AVPacket* avpkt)
 
 
 
+#include "imageio_pvt.h"
 #include <OpenImageIO/color.h>
 #include <OpenImageIO/imageio.h>
 #include <iostream>
@@ -549,11 +550,7 @@ FFmpegInput::open(const std::string& name, ImageSpec& spec)
         = { m_codec_context->color_primaries, m_codec_context->color_trc,
             m_codec_context->colorspace,
             m_codec_context->color_range == AVCOL_RANGE_MPEG ? 0 : 1 };
-    m_spec.attribute("CICP", TypeDesc(TypeDesc::INT, 4), cicp);
-    const ColorConfig& colorconfig(ColorConfig::default_colorconfig());
-    string_view interop_id = colorconfig.get_color_interop_id(cicp);
-    if (!interop_id.empty())
-        m_spec.attribute("oiio:ColorSpace", interop_id);
+    pvt::set_colorspace_cicp(spec, cicp);
 
     m_nsubimages = m_frames;
     spec         = m_spec;

src/gif.imageio/gifinput.cpp

@@ -12,6 +12,8 @@
 #include <OpenImageIO/imageio.h>
 #include <OpenImageIO/thread.h>
 
+#include "imageio_pvt.h"
+
 // GIFLIB:
 // http://giflib.sourceforge.net/
 // Format description:
@@ -259,7 +261,7 @@ GIFInput::read_subimage_metadata(ImageSpec& newspec)
     newspec.nchannels = 4;
     newspec.default_channel_names();
     newspec.alpha_channel = 4;
-    newspec.set_colorspace("srgb_rec709_scene");
+    pvt::set_colorspace_srgb(newspec);
 
     m_previous_disposal_method = m_disposal_method;
     m_disposal_method          = DISPOSAL_UNSPECIFIED;

src/heif.imageio/heifinput.cpp

@@ -9,6 +9,8 @@
 #include <OpenImageIO/platform.h>
 #include <OpenImageIO/tiffutils.h>
 
+#include "imageio_pvt.h"
+
 #include <libheif/heif_cxx.h>
 
 #define MAKE_LIBHEIF_VERSION(a, b, c, d) \
@@ -273,7 +275,7 @@ HeifInput::seek_subimage(int subimage, int miplevel)
     if (m_bitdepth > 8) {
         m_spec.attribute("oiio:BitsPerSample", m_bitdepth);
     }
-    m_spec.set_colorspace("srgb_rec709_scene");
+    pvt::set_colorspace_srgb(m_spec);
 
 #if LIBHEIF_HAVE_VERSION(1, 9, 0)
     // Read CICP. Have to use the C API to get it from the image handle,
@@ -292,12 +294,7 @@ HeifInput::seek_subimage(int subimage, int miplevel)
                                       int(nclx->transfer_characteristics),
                                       int(nclx->matrix_coefficients),
                                       int(nclx->full_range_flag ? 1 : 0) };
-                m_spec.attribute("CICP", TypeDesc(TypeDesc::INT, 4), cicp);
-                const ColorConfig& colorconfig(
-                    ColorConfig::default_colorconfig());
-                string_view interop_id = colorconfig.get_color_interop_id(cicp);
-                if (!interop_id.empty())
-                    m_spec.attribute("oiio:ColorSpace", interop_id);
+                pvt::set_colorspace_cicp(m_spec, cicp);
             }
             heif_nclx_color_profile_free(nclx);
         }

src/iconvert/iconvert.cpp

@@ -18,6 +18,8 @@
 #include <OpenImageIO/strutil.h>
 #include <OpenImageIO/sysutil.h>
 
+#include "imageio_pvt.h"
+
 
 using namespace OIIO;
 
@@ -224,7 +226,7 @@ adjust_spec(ImageInput* in, ImageOutput* out, const ImageSpec& inspec,
     if (gammaval != 1.0f)
         outspec.attribute("oiio:Gamma", gammaval);
     if (sRGB) {
-        outspec.set_colorspace("srgb_rec709_scene");
+        pvt::set_colorspace_srgb(outspec);
         if (!strcmp(in->format_name(), "jpeg")
             || outspec.find_attribute("Exif:ColorSpace"))
             outspec.attribute("Exif:ColorSpace", 1);

src/include/OpenImageIO/color.h

@@ -415,10 +415,13 @@ class OIIO_API ColorConfig {
     string_view get_color_interop_id(string_view colorspace) const;
 
     /// Find color interop ID corresponding to the CICP code.
+    /// If prefer_scene_referred is true, prefer returning a scene referred
+    /// interop ID over a display referred interop ID if both exist.
     /// Returns empty string if not found.
     ///
     /// @version 3.1
-    string_view get_color_interop_id(const int cicp[4]) const;
+    string_view get_color_interop_id(const int cicp[4],
+                                     bool prefer_scene_referred) const;
 
     /// Return a filename or other identifier for the config we're using.
     std::string configname() const;

src/include/imageio_pvt.h

@@ -127,6 +127,14 @@ parallel_convert_from_float(const float* src, void* dst, size_t nvals,
 OIIO_API bool
 check_texture_metadata_sanity(ImageSpec& spec);
 
+/// Set oiio:ColorSpace to the default sRGB colorspace, which may be display
+/// or scene referred depending on configuration.
+///
+/// If erase_other_attributes is true, other potentially conflicting attributes
+/// are erased.
+OIIO_API void
+set_colorspace_srgb(ImageSpec& spec, bool erase_other_attributes = true);
+
 /// Returns true if for the purpose of interop, the spec's metadata
 /// specifies a color space that should be encoded as sRGB.
 ///
@@ -143,13 +151,18 @@ get_colorspace_rec709_gamma(const ImageSpec& spec);
 // Returns ICC profile from the spec's metadata, either from an ICCProfile
 // attribute or from the colorspace if from_colorspace is true.
 // Returns an empty vector if not found.
-std::vector<uint8_t>
+OIIO_API std::vector<uint8_t>
 get_colorspace_icc_profile(const ImageSpec& spec, bool from_colorspace = true);
 
-// Returns ICC profile from the spec's metadata, either from a CICP attribute
+// Set CICP attribute in the spec's metadata, and set oiio:ColorSpace
+// along with it if there is a corresponding known colorspace.
+OIIO_API void
+set_colorspace_cicp(ImageSpec& spec, const int cicp[4]);
+
+// Returns CICP from the spec's metadata, either from a CICP attribute
 // or from the colorspace if from_colorspace is true.
 // Returns an empty span if not found.
-cspan<int>
+OIIO_API cspan<int>
 get_colorspace_cicp(const ImageSpec& spec, bool from_colorspace = true);
 
 /// Get the timing report from log_time entries.