feat: Auto convert between oiio:ColorSpace and CICP attributes in I/O

When reading image files with CICP metadata, automatically set the
corresponding "oiio:ColorSpace". When writing files that support CICP and no
other colorspace metadata can represent "oiio:ColorSpace", automatically write
CICP metadata.

Setting "oiio:ColorSpace" on read prefers scene referred over display referred
color spaces, changing existing behavior as little as possible. The alternative
would have been to interpret the presence of CICP metadata as an indication
that the image is likely display referred, which might be reasonable too.

Also add new ColorConfig set_colorspace_cicp and get_colorspace_cicp API
functions to share logic between file formats.

Author: brechtvl

src/ffmpeg.imageio/ffmpeginput.cpp

@@ -71,6 +71,7 @@ receive_frame(AVCodecContext* avctx, AVFrame* picture, AVPacket* avpkt)
 
 
 
+#include <OpenImageIO/color.h>
 #include <OpenImageIO/imageio.h>
 #include <iostream>
 #include <mutex>
@@ -548,7 +549,8 @@ 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);
+    ColorConfig::default_colorconfig().set_colorspace_cicp(m_spec, cicp);
+
     m_nsubimages = m_frames;
     spec         = m_spec;
     m_filename   = name;

src/heif.imageio/heifinput.cpp

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 // https://github.com/AcademySoftwareFoundation/OpenImageIO
 
+#include <OpenImageIO/color.h>
 #include <OpenImageIO/filesystem.h>
 #include <OpenImageIO/fmath.h>
 #include <OpenImageIO/imageio.h>
@@ -291,7 +292,9 @@ 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());
+                colorconfig.set_colorspace_cicp(m_spec, cicp);
             }
             heif_nclx_color_profile_free(nclx);
         }

src/heif.imageio/heifoutput.cpp

@@ -3,6 +3,7 @@
 // https://github.com/AcademySoftwareFoundation/OpenImageIO
 
 
+#include <OpenImageIO/color.h>
 #include <OpenImageIO/filesystem.h>
 #include <OpenImageIO/fmath.h>
 #include <OpenImageIO/imageio.h>
@@ -249,10 +250,10 @@ HeifOutput::close()
         std::unique_ptr<heif_color_profile_nclx,
                         void (*)(heif_color_profile_nclx*)>
             nclx(heif_nclx_color_profile_alloc(), heif_nclx_color_profile_free);
-        const ParamValue* p = m_spec.find_attribute("CICP",
-                                                    TypeDesc(TypeDesc::INT, 4));
-        if (p) {
-            const int* cicp                = static_cast<const int*>(p->data());
+        const ColorConfig& colorconfig(ColorConfig::default_colorconfig());
+        const bool auto_cicp = true;
+        int cicp[4];
+        if (colorconfig.get_colorspace_cicp(m_spec, auto_cicp, cicp)) {
             nclx->color_primaries          = heif_color_primaries(cicp[0]);
             nclx->transfer_characteristics = heif_transfer_characteristics(
                 cicp[1]);

src/include/OpenImageIO/color.h

@@ -422,6 +422,23 @@ class OIIO_API ColorConfig {
     /// @version 3.0
     void set_colorspace_rec709_gamma(ImageSpec& spec, float gamma) const;
 
+    /// Set the "CICP" attribute in the spec. If a corresponding colorspace
+    /// is found, automatically set "oiio:ColorSpace" as well. It also removes
+    /// or alters several other attributes that may hint color space in ways
+    /// that might be contradictory or no longer true.
+    ///
+    /// @version 3.1
+    void set_colorspace_cicp(ImageSpec& spec, const int cicp[4]) const;
+
+    /// Get the CICP code corresponding from the "CICP" attribute. If there
+    /// is not such attribute and auto_cicp is true, atempt to determine a CICP
+    /// code from the "oiio:ColorSpace" attribute.
+    /// Returns false if no CICP code could be determined.
+    ///
+    /// @version 3.1
+    bool get_colorspace_cicp(ImageSpec& spec, bool auto_colorspace,
+                             int cicp[4]) const;
+
     /// Return if OpenImageIO was built with OCIO support
     static bool supportsOpenColorIO();
 

src/libOpenImageIO/color_ocio.cpp

@@ -2655,6 +2655,140 @@ ColorConfig::set_colorspace_rec709_gamma(ImageSpec& spec, float gamma) const
     }
 }
 
+namespace {
+// Primaries
+static const int cicp_primaries_rec709  = 1;
+static const int cicp_primaries_rec2020 = 9;
+static const int cicp_primaries_xyzd65  = 10;
+static const int cicp_primaries_p3d65   = 12;
+// Transfer functions
+static const int cicp_transfer_bt709  = 1;
+static const int cicp_transfer_g22    = 4;
+static const int cicp_transfer_linear = 8;
+static const int cicp_transfer_srgb   = 13;
+static const int cicp_transfer_pq     = 16;
+static const int cicp_transfer_g26    = 17;
+static const int cicp_transfer_hlg    = 18;
+// Matrix
+static const int cicp_matrix_bt709       = 1;
+static const int cicp_matrix_unspecified = 2;
+static const int cicp_matrix_rec2020_ncl = 9;
+static const int cicp_matrix_rec2020_cl  = 10;
+// Range
+static const int cicp_range_full = 1;
+
+// Mapping between color interop ID and CICP, based on Color Interop Forum
+// recommendations.
+struct ColorSpaceCICP {
+    const char* interop_id;
+    int cicp[4];
+};
+
+static const ColorSpaceCICP color_space_cicp[] = {
+    // Scene referred interop IDs first so they are the default in automatic
+    // conversion from CICP to interop ID.
+    { "srgb_rec709_scene",
+      { cicp_primaries_rec709, cicp_transfer_srgb, cicp_matrix_bt709,
+        cicp_range_full } },
+    { "srgb_rec709_scene",
+      { cicp_primaries_rec709, cicp_transfer_srgb, cicp_matrix_bt709,
+        cicp_range_full } },
+    { "srgb_p3d65_scene",
+      { cicp_primaries_p3d65, cicp_transfer_srgb, cicp_matrix_bt709,
+        cicp_range_full } },
+    // These are not display color spaces at all, but can be represented by CICP.
+    { "lin_rec709_scene",
+      { cicp_primaries_rec709, cicp_transfer_linear, cicp_matrix_bt709,
+        cicp_range_full } },
+    { "lin_p3d65_scene",
+      { cicp_primaries_p3d65, cicp_transfer_linear, cicp_matrix_bt709,
+        cicp_range_full } },
+    { "lin_rec2020_scene",
+      { cicp_primaries_rec2020, cicp_transfer_linear, cicp_matrix_rec2020_cl,
+        cicp_range_full } },
+    { "lin_ciexyzd65_scene",
+      { cicp_primaries_xyzd65, cicp_transfer_linear, cicp_matrix_unspecified,
+        cicp_range_full } },
+
+    // Display referred interop IDs.
+    { "srgb_rec709_display",
+      { cicp_primaries_rec709, cicp_transfer_srgb, cicp_matrix_bt709,
+        cicp_range_full } },
+    { "g24_rec709_display",
+      { cicp_primaries_rec709, cicp_transfer_bt709, cicp_matrix_bt709,
+        cicp_range_full } },
+    { "srgb_p3d65_display",
+      { cicp_primaries_p3d65, cicp_transfer_srgb, cicp_matrix_bt709,
+        cicp_range_full } },
+    { "srgbe_p3d65_display",
+      { cicp_primaries_p3d65, cicp_transfer_srgb, cicp_matrix_bt709,
+        cicp_range_full } },
+    { "pq_p3d65_display",
+      { cicp_primaries_p3d65, cicp_transfer_pq, cicp_matrix_rec2020_ncl,
+        cicp_range_full } },
+    { "pq_rec2020_display",
+      { cicp_primaries_rec2020, cicp_transfer_pq, cicp_matrix_rec2020_ncl,
+        cicp_range_full } },
+    { "hlg_rec2020_display",
+      { cicp_primaries_rec2020, cicp_transfer_hlg, cicp_matrix_rec2020_ncl,
+        cicp_range_full } },
+    { "g22_rec709_display",
+      { cicp_primaries_rec709, cicp_transfer_g22, cicp_matrix_bt709,
+        cicp_range_full } },
+    // No CICP code for Adobe RGB primaries.
+    // { "g22_adobergb_display" }
+    { "g26_p3d65_display",
+      { cicp_primaries_p3d65, cicp_transfer_g26, cicp_matrix_bt709,
+        cicp_range_full } },
+    { "g26_xyzd65_display",
+      { cicp_primaries_xyzd65, cicp_transfer_g26, cicp_matrix_unspecified,
+        cicp_range_full } },
+    { "pq_xyzd65_display",
+      { cicp_primaries_xyzd65, cicp_transfer_pq, cicp_matrix_unspecified,
+        cicp_range_full } },
+};
+}  // namespace
+
+void
+ColorConfig::set_colorspace_cicp(ImageSpec& spec, const int cicp[4]) const
+{
+    spec.attribute("CICP", TypeDesc(TypeDesc::INT, 4), cicp);
+
+    for (const ColorSpaceCICP& space : color_space_cicp) {
+        if (space.cicp[0] == cicp[0] && space.cicp[1] == cicp[1]) {
+            set_colorspace(spec, space.interop_id);
+            return;
+        }
+    }
+}
+
+bool
+ColorConfig::get_colorspace_cicp(ImageSpec& spec, bool auto_cicp,
+                                 int cicp[4]) const
+{
+    const ParamValue* p = spec.find_attribute("CICP",
+                                              TypeDesc(TypeDesc::INT, 4));
+    if (p) {
+        std::copy_n(static_cast<const int*>(p->data()), 4, cicp);
+        return true;
+    }
+
+    if (!auto_cicp) {
+        return false;
+    }
+
+    string_view colorspace = spec.get_string_attribute("oiio:ColorSpace");
+    if (!colorspace.empty()) {
+        for (const ColorSpaceCICP& space : color_space_cicp) {
+            if (equivalent(colorspace, space.interop_id)) {
+                std::copy_n(space.cicp, 4, cicp);
+                return true;
+            }
+        }
+    }
+
+    return false;
+}
 
 void
 set_colorspace(ImageSpec& spec, string_view colorspace)

src/png.imageio/png_pvt.h

@@ -40,7 +40,6 @@ For further information see the following mailing list threads:
 OIIO_PLUGIN_NAMESPACE_BEGIN
 
 #define ICC_PROFILE_ATTR "ICCProfile"
-#define CICP_ATTR "CICP"
 
 namespace PNG_pvt {
 
@@ -330,8 +329,9 @@ read_info(png_structp& sp, png_infop& ip, int& bit_depth, int& color_type,
     {
         png_byte pri = 0, trc = 0, mtx = 0, vfr = 0;
         if (png_get_cICP(sp, ip, &pri, &trc, &mtx, &vfr)) {
-            int cicp[4] = { pri, trc, mtx, vfr };
-            spec.attribute(CICP_ATTR, TypeDesc(TypeDesc::INT, 4), cicp);
+            const int cicp[4] = { pri, trc, mtx, vfr };
+            const ColorConfig& colorconfig(ColorConfig::default_colorconfig());
+            colorconfig.set_colorspace_cicp(spec, cicp);
         }
     }
 #endif
@@ -608,7 +608,8 @@ write_info(png_structp& sp, png_infop& ip, int& color_type, ImageSpec& spec,
     string_view colorspace = spec.get_string_attribute("oiio:ColorSpace",
                                                        "srgb_rec709_scene");
     const ColorConfig& colorconfig(ColorConfig::default_colorconfig());
-    srgb = false;
+    bool wrote_colorspace = false;
+    srgb                  = false;
     if (colorconfig.equivalent(colorspace, "srgb_rec709_scene")) {
         srgb  = true;
         gamma = 1.0f;
@@ -628,7 +629,8 @@ write_info(png_structp& sp, png_infop& ip, int& color_type, ImageSpec& spec,
         if (setjmp(png_jmpbuf(sp)))  // NOLINT(cert-err52-cpp)
             return "Could not set PNG gAMA chunk";
         png_set_gAMA(sp, ip, 1.0);
-        srgb = false;
+        srgb             = false;
+        wrote_colorspace = true;
     } else if (Strutil::istarts_with(colorspace, "Gamma")) {
         // Back compatible, this is DEPRECATED(3.1)
         Strutil::parse_word(colorspace);
@@ -638,24 +640,28 @@ write_info(png_structp& sp, png_infop& ip, int& color_type, ImageSpec& spec,
         if (setjmp(png_jmpbuf(sp)))  // NOLINT(cert-err52-cpp)
             return "Could not set PNG gAMA chunk";
         png_set_gAMA(sp, ip, 1.0f / gamma);
-        srgb = false;
+        srgb             = false;
+        wrote_colorspace = true;
     } else if (colorconfig.equivalent(colorspace, "g22_rec709_scene")) {
         gamma = 2.2f;
         if (setjmp(png_jmpbuf(sp)))  // NOLINT(cert-err52-cpp)
             return "Could not set PNG gAMA chunk";
         png_set_gAMA(sp, ip, 1.0f / gamma);
-        srgb = false;
+        srgb             = false;
+        wrote_colorspace = true;
     } else if (colorconfig.equivalent(colorspace, "g18_rec709_scene")) {
         gamma = 1.8f;
         if (setjmp(png_jmpbuf(sp)))  // NOLINT(cert-err52-cpp)
             return "Could not set PNG gAMA chunk";
         png_set_gAMA(sp, ip, 1.0f / gamma);
-        srgb = false;
+        srgb             = false;
+        wrote_colorspace = true;
     } else if (colorconfig.equivalent(colorspace, "srgb_rec709_scene")) {
         if (setjmp(png_jmpbuf(sp)))  // NOLINT(cert-err52-cpp)
             return "Could not set PNG gAMA and cHRM chunk";
         png_set_sRGB_gAMA_and_cHRM(sp, ip, PNG_sRGB_INTENT_ABSOLUTE);
-        srgb = true;
+        srgb             = true;
+        wrote_colorspace = true;
     }
 
     // Write ICC profile, if we have anything
@@ -667,8 +673,10 @@ write_info(png_structp& sp, png_infop& ip, int& color_type, ImageSpec& spec,
             return "Could not set PNG iCCP chunk";
         unsigned char* icc_profile
             = (unsigned char*)icc_profile_parameter->data();
-        if (icc_profile && length)
+        if (icc_profile && length) {
             png_set_iCCP(sp, ip, "Embedded Profile", 0, icc_profile, length);
+            wrote_colorspace = true;
+        }
     }
 
     if (false && !spec.find_attribute("DateTime")) {
@@ -724,13 +732,16 @@ write_info(png_structp& sp, png_infop& ip, int& color_type, ImageSpec& spec,
     }
 
 #ifdef PNG_cICP_SUPPORTED
-    const ParamValue* p = spec.find_attribute(CICP_ATTR,
-                                              TypeDesc(TypeDesc::INT, 4));
-    if (p) {
-        const int* int_vals = static_cast<const int*>(p->data());
+    // Only automatically determine CICP from oiio::ColorSpace if we didn't
+    // write colorspace metadata yet.
+    const bool auto_cicp = !wrote_colorspace;
+    int cicp[4];
+    if (colorconfig.get_colorspace_cicp(spec, auto_cicp, cicp)) {
+        // Matrix must be RGB according to PNG spec v3
+        cicp[2] = 0;
         png_byte vals[4];
         for (int i = 0; i < 4; ++i)
-            vals[i] = static_cast<png_byte>(int_vals[i]);
+            vals[i] = static_cast<png_byte>(cicp[i]);
         if (setjmp(png_jmpbuf(sp)))  // NOLINT(cert-err52-cpp)
             return "Could not set PNG cICP chunk";
         // libpng will only write the chunk if the third byte is 0

testsuite/ffmpeg/ref/out-ffmpeg6.1.txt

@@ -96,6 +96,7 @@ ref/vp9_rec2100_pq.mkv :  384 x  216, 3 channel, uint10 FFmpeg movie
     FramesPerSecond: 24/1 (24)
     ffmpeg:codec_name: "Google VP9"
     oiio:BitsPerSample: 10
+    oiio:ColorSpace: "pq_rec2020_display"
     oiio:Movie: 1
     oiio:subimages: 2
  subimage  1:  384 x  216, 3 channel, uint10 FFmpeg movie
@@ -106,5 +107,6 @@ ref/vp9_rec2100_pq.mkv :  384 x  216, 3 channel, uint10 FFmpeg movie
     FramesPerSecond: 24/1 (24)
     ffmpeg:codec_name: "Google VP9"
     oiio:BitsPerSample: 10
+    oiio:ColorSpace: "pq_rec2020_display"
     oiio:Movie: 1
     oiio:subimages: 2

testsuite/ffmpeg/ref/out-ffmpeg8.0.txt

@@ -96,6 +96,7 @@ ref/vp9_rec2100_pq.mkv :  384 x  216, 3 channel, uint10 FFmpeg movie
     FramesPerSecond: 24/1 (24)
     ffmpeg:codec_name: "Google VP9"
     oiio:BitsPerSample: 10
+    oiio:ColorSpace: "pq_rec2020_display"
     oiio:Movie: 1
     oiio:subimages: 2
  subimage  1:  384 x  216, 3 channel, uint10 FFmpeg movie
@@ -106,5 +107,6 @@ ref/vp9_rec2100_pq.mkv :  384 x  216, 3 channel, uint10 FFmpeg movie
     FramesPerSecond: 24/1 (24)
     ffmpeg:codec_name: "Google VP9"
     oiio:BitsPerSample: 10
+    oiio:ColorSpace: "pq_rec2020_display"
     oiio:Movie: 1
     oiio:subimages: 2

testsuite/heif/ref/out-libheif1.12-orient.txt

@@ -64,7 +64,17 @@ cicp_pq.avif         :   16 x   16, 4 channel, uint10 heif
     Exif:FlashPixVersion: "0100"
     heif:UnassociatedAlpha: 1
     oiio:BitsPerSample: 10
-    oiio:ColorSpace: "srgb_rec709_scene"
+    oiio:ColorSpace: "pq_rec2020_display"
+Reading colorspace_hlg.avif
+colorspace_hlg.avif  :   16 x   16, 4 channel, uint10 heif
+    SHA-1: 0F3CAB52D479BC23E9C981DBADDFEF1F792E5540
+    channel list: R, G, B, A
+    CICP: 9, 18, 9, 1
+    Exif:ExifVersion: "0230"
+    Exif:FlashPixVersion: "0100"
+    heif:UnassociatedAlpha: 1
+    oiio:BitsPerSample: 10
+    oiio:ColorSpace: "hlg_rec2020_display"
 Reading ../oiio-images/heif/greyhounds-looking-for-a-table.heic
 ../oiio-images/heif/greyhounds-looking-for-a-table.heic : 3024 x 4032, 3 channel, uint8 heif
     SHA-1: 8211F56BBABDC7615CCAF67CBF49741D1A292D2E

testsuite/heif/ref/out-libheif1.4.txt

@@ -64,7 +64,17 @@ cicp_pq.avif         :   16 x   16, 4 channel, uint10 heif
     Exif:FlashPixVersion: "0100"
     heif:UnassociatedAlpha: 1
     oiio:BitsPerSample: 10
-    oiio:ColorSpace: "srgb_rec709_scene"
+    oiio:ColorSpace: "pq_rec2020_display"
+Reading colorspace_hlg.avif
+colorspace_hlg.avif  :   16 x   16, 4 channel, uint10 heif
+    SHA-1: 0F3CAB52D479BC23E9C981DBADDFEF1F792E5540
+    channel list: R, G, B, A
+    CICP: 9, 18, 9, 1
+    Exif:ExifVersion: "0230"
+    Exif:FlashPixVersion: "0100"
+    heif:UnassociatedAlpha: 1
+    oiio:BitsPerSample: 10
+    oiio:ColorSpace: "hlg_rec2020_display"
 Reading ../oiio-images/heif/greyhounds-looking-for-a-table.heic
 ../oiio-images/heif/greyhounds-looking-for-a-table.heic : 3024 x 4032, 3 channel, uint8 heif
     SHA-1: 8211F56BBABDC7615CCAF67CBF49741D1A292D2E