feat(openexr): Follow CIF for color interop ID in multi-part files

src/cmake/testing.cmake

@@ -469,6 +469,9 @@ macro (oiio_add_all_tests)
     # Self-contained decompression-bomb regression (ships its own tiny fixture);
     # exercises both the C++ and C-API readers via the openexr:core attribute.
     oiio_add_tests (openexr-bomb)
+    # Self-contained multi-part colorInteropID inheritance test (ships its own
+    # tiny fixture); exercises both the C++ and C-API readers.
+    oiio_add_tests (openexr-multipart-colorspace)
     # if (NOT DEFINED ENV{${PROJECT_NAME}_CI})
     #     oiio_add_tests (openexr-damaged
     #                     IMAGEDIR openexr-images

src/openexr.imageio/exr_pvt.h

@@ -232,6 +232,7 @@ class OpenEXRInput final : public ImageInput {
     int m_miplevel;                     ///< What MIP level are we looking at?
     std::vector<float> m_missingcolor;  ///< Color for missing tile/scanline
     std::string m_filename;             // filename, if known
+    std::string m_file_color_interop_id;
 
     void init()
     {
@@ -248,6 +249,7 @@ class OpenEXRInput final : public ImageInput {
         m_local_io.reset();
         m_missingcolor.clear();
         m_filename.clear();
+        m_file_color_interop_id.clear();
     }
 
     bool read_native_scanlines_individually(int subimage, int miplevel,

src/openexr.imageio/exrinput.cpp

@@ -218,6 +218,17 @@ OpenEXRInput::valid_file(Filesystem::IOProxy* ioproxy) const
 
 
 
+// Color space shared by all parts of the file, taken from the first part.
+static std::string
+file_color_interop_id(const Imf::MultiPartInputFile* multipart)
+{
+    const Imf::StringAttribute* attr
+        = multipart->header(0).findTypedAttribute<Imf::StringAttribute>(
+            "colorInteropID");
+    return attr ? attr->value() : std::string();
+}
+
+
 bool
 OpenEXRInput::open(const std::string& name, ImageSpec& newspec,
                    const ImageSpec& config)
@@ -326,6 +337,8 @@ OpenEXRInput::open(const std::string& name, ImageSpec& newspec,
     m_subimage = -1;
     m_miplevel = -1;
 
+    m_file_color_interop_id = file_color_interop_id(m_input_multipart);
+
     // Set up for the first subimage ("part"). This will trigger reading
     // information about all the parts.
     bool ok = seek_subimage(0, 0);
@@ -731,8 +744,15 @@ OpenEXRInput::PartInfo::parse_header(OpenEXRInput* in,
     // Try to figure out the color space for some unambiguous cases
     if (spec.get_int_attribute("acesImageContainerFlag") == 1) {
         spec.set_colorspace("lin_ap0_scene");
-    } else if (auto c = spec.find_attribute("colorInteropID", TypeString)) {
-        spec.set_colorspace(c->get_ustring());
+    } else {
+        // Follow the color interop forum recommendation for OpenEXR files,
+        // inheriting the colorInteropID from the first part.
+        string_view interop_id = spec.get_string_attribute("colorInteropID");
+        if (!interop_id.empty()) {
+            spec.set_colorspace(interop_id);
+        } else if (!in->m_file_color_interop_id.empty()) {
+            spec.set_colorspace(in->m_file_color_interop_id);
+        }
     }
 
     // Squash some problematic texture metadata if we suspect it's wrong

src/openexr.imageio/exrinput_c.cpp

@@ -212,6 +212,7 @@ class OpenEXRCoreInput final : public ImageInput {
     int m_nsubimages;                   ///< How many subimages are there?
     std::vector<float> m_missingcolor;  ///< Color for missing tile/scanline
     std::string m_filename;             // filename, if known
+    std::string m_file_color_interop_id;
 
     void init()
     {
@@ -221,6 +222,7 @@ class OpenEXRCoreInput final : public ImageInput {
         m_local_io.reset();
         m_missingcolor.clear();
         m_filename.clear();
+        m_file_color_interop_id.clear();
     }
 
     bool valid_file_or_proxy(const std::string& filename,
@@ -340,6 +342,21 @@ OpenEXRCoreInput::valid_file_or_proxy(const std::string& filename,
 
 
 
+// Color space shared by all parts of the file, taken from the first part.
+static std::string
+file_color_interop_id(exr_context_t ctxt)
+{
+    int32_t length      = 0;
+    const char* interop = nullptr;
+    if (exr_attr_get_string(ctxt, 0, "colorInteropID", &length, &interop)
+            != EXR_ERR_SUCCESS
+        || !interop)
+        return std::string();
+
+    return std::string(interop, size_t(length));
+}
+
+
 bool
 OpenEXRCoreInput::open(const std::string& name, ImageSpec& newspec,
                        const ImageSpec& config)
@@ -439,6 +456,8 @@ OpenEXRCoreInput::open(const std::string& name, ImageSpec& newspec,
     m_subimage = -1;
     m_miplevel = -1;
 
+    m_file_color_interop_id = file_color_interop_id(m_exr_context);
+
     // Set up for the first subimage ("part"). This will trigger reading
     // information about all the parts.
     bool ok = seek_subimage(0, 0);
@@ -825,8 +844,15 @@ OpenEXRCoreInput::PartInfo::parse_header(OpenEXRCoreInput* in,
     // Try to figure out the color space for some unambiguous cases
     if (spec.get_int_attribute("acesImageContainerFlag") == 1) {
         spec.set_colorspace("lin_ap0_scene");
-    } else if (auto c = spec.find_attribute("colorInteropID", TypeString)) {
-        spec.set_colorspace(c->get_ustring());
+    } else {
+        // Follow the color interop forum recommendation for OpenEXR files,
+        // inheriting the colorInteropID from the first part.
+        string_view interop_id = spec.get_string_attribute("colorInteropID");
+        if (!interop_id.empty()) {
+            spec.set_colorspace(interop_id);
+        } else if (!in->m_file_color_interop_id.empty()) {
+            spec.set_colorspace(in->m_file_color_interop_id);
+        }
     }
 
     // Squash some problematic texture metadata if we suspect it's wrong

src/openexr.imageio/exroutput.cpp

@@ -710,6 +710,39 @@ OpenEXROutput::open(const std::string& name, const ImageSpec& userspec,
 }
 
 
+// Follow the color interop forum recommendation for OpenEXR files,
+// where the colorInteropID in later parts must match the first part,
+// except when "data" or missing.
+static std::string
+validate_color_interop_ids(const std::vector<Imf::Header>& headers)
+{
+    string_view file_interop_id;
+
+    for (size_t s = 0; s < headers.size(); ++s) {
+        const Imf::StringAttribute* attr
+            = headers[s].findTypedAttribute<Imf::StringAttribute>(
+                "colorInteropID");
+        string_view interop_id = attr ? string_view(attr->value())
+                                      : string_view();
+
+        if (s == 0) {
+            file_interop_id = interop_id;
+            continue;
+        }
+
+        if (interop_id.empty() || interop_id == "data"
+            || interop_id == file_interop_id)
+            continue;
+
+        return Strutil::fmt::format(
+            "OpenEXR subimage {} has color space \"{}\", different from \"{}\" in the first subimage",
+            s, interop_id, file_interop_id);
+    }
+
+    return "";
+}
+
+
 
 bool
 OpenEXROutput::open(const std::string& name, int subimages,
@@ -758,6 +791,12 @@ OpenEXROutput::open(const std::string& name, int subimages,
         }
     }
 
+    std::string interop_id_error = validate_color_interop_ids(m_headers);
+    if (!interop_id_error.empty()) {
+        errorfmt("{}", interop_id_error);
+        return false;
+    }
+
     m_spec = m_subimagespecs[0];
     sanity_check_channelnames();
     compute_pixeltypes(m_spec);