InternationalColorConsortium · xsscx · Apr 13, 2026 · Apr 13, 2026
@@ -82,8 +82,8 @@ static IccJson icJsonGetHeaderFlags(icUInt32Number flags)
   j["UseWithEmbeddedDataOnly"] = (bool)(flags & icUseWithEmbeddedDataOnly);
   if (flags & icExtendedRangePCS) j["ExtendedRangePCS"] = true;
   if (flags & icMCSNeedsSubsetTrue) j["MCSNeedsSubset"] = true;
-  icUInt32Number other = flags & ~(icEmbeddedProfileTrue | icUseWithEmbeddedDataOnly |
-                                    icExtendedRangePCS | icMCSNeedsSubsetTrue);
+  icUInt32Number other = flags & ~(icUInt32Number)(icEmbeddedProfileTrue | icUseWithEmbeddedDataOnly |
+                                                   icExtendedRangePCS | icMCSNeedsSubsetTrue);
   if (other) {
     char buf[16]; snprintf(buf, sizeof(buf), "%08x", other);
     j["VendorFlags"] = buf;

@@ -727,11 +727,17 @@ bool CIccTagJsonColorantOrder::ParseJson(const IccJson &j, std::string & /*parse
 
 bool CIccTagJsonColorantTable::ToJson(IccJson &j)
 {
+  j["pcsEncoding"] = "Lab";
   IccJson arr = IccJson::array();
   for (icUInt32Number i = 0; i < m_nCount; i++) {
+    icFloatNumber pcs[3];
+    pcs[0] = icU16toF(m_pData[i].data[0]);
+    pcs[1] = icU16toF(m_pData[i].data[1]);
+    pcs[2] = icU16toF(m_pData[i].data[2]);
+    icLabFromPcs(pcs);
     IccJson c;
     c["name"] = m_pData[i].name;
-    c["pcs"]  = IccJson::array({ m_pData[i].data[0], m_pData[i].data[1], m_pData[i].data[2] });
+    c["pcs"]  = IccJson::array({ pcs[0], pcs[1], pcs[2] });
     arr.push_back(c);
   }
   j["colorantTable"] = arr;
@@ -740,6 +746,9 @@ bool CIccTagJsonColorantTable::ToJson(IccJson &j)
 
 bool CIccTagJsonColorantTable::ParseJson(const IccJson &j, std::string & /*parseStr*/)
 {
+  std::string pcsEncoding = "Lab";
+  jGetString(j, "pcsEncoding", pcsEncoding);
+
   if (jsonExistsField(j, "colorantTable") && j["colorantTable"].is_array()) {
     const IccJson &arr = j["colorantTable"];
     if (!SetSize((icUInt32Number)arr.size())) return false;
@@ -748,8 +757,21 @@ bool CIccTagJsonColorantTable::ParseJson(const IccJson &j, std::string & /*parse
       std::string name;
       if (jGetString(c, "name", name))
         strncpy(m_pData[i].name, name.c_str(), sizeof(m_pData[i].name)-1);
-      if (jsonExistsField(c, "pcs") && c["pcs"].is_array() && c["pcs"].size() >= 3)
-        jGetArray(c, "pcs", m_pData[i].data, 3);
+      if (jsonExistsField(c, "pcs") && c["pcs"].is_array() && c["pcs"].size() >= 3) {
+        if (pcsEncoding == "16bit") {
+          jGetArray(c, "pcs", m_pData[i].data, 3);
+        } else {
+          icFloatNumber pcs[3];
+          jGetArray(c, "pcs", pcs, 3);
+          if (pcsEncoding == "XYZ")
+            icXyzToPcs(pcs);
+          else  // "Lab" (default)
+            icLabToPcs(pcs);
+          m_pData[i].data[0] = icFtoU16(pcs[0]);
+          m_pData[i].data[1] = icFtoU16(pcs[1]);
+          m_pData[i].data[2] = icFtoU16(pcs[2]);
+        }
+      }
     }
   }
   return true;
@@ -1386,24 +1408,38 @@ bool CIccTagJsonCurve::ToJson(IccJson &j, icConvertType nType)
     j["curveType"] = "gamma";
     j["gamma"] = (double)m_Curve[0];
   } else {
-    j["curveType"] = "table";
-    IccJson arr = IccJson::array();
-    for (icUInt32Number i = 0; i < m_nSize; i++) {
-      switch (nType) {
-        case icConvert8Bit:
-          arr.push_back((int)(m_Curve[i] * 255.0f + 0.5f)); break;
-        case icConvert16Bit:
-        case icConvertVariable:
-          arr.push_back((int)(m_Curve[i] * 65535.0f + 0.5f)); break;
-        default:
-          arr.push_back((double)m_Curve[i]); break;
+    // Check whether the table is a sampled identity (linear ramp 0..1).
+    // Tolerance of 0.5/65535 covers 16-bit quantisation rounding.
+    bool isIdentity = true;
+    const icFloatNumber tol = 0.5f / 65535.0f;
+    for (icUInt32Number i = 0; i < m_nSize && isIdentity; i++) {
+      icFloatNumber expected = (icFloatNumber)i / (icFloatNumber)(m_nSize - 1);
+      if (fabsf(m_Curve[i] - expected) > tol)
+        isIdentity = false;
+    }
+    if (isIdentity) {
+      j["curveType"] = "identity";
+      j["size"] = (int)m_nSize;
+    } else {
+      j["curveType"] = "table";
+      IccJson arr = IccJson::array();
+      for (icUInt32Number i = 0; i < m_nSize; i++) {
+        switch (nType) {
+          case icConvert8Bit:
+            arr.push_back((int)(m_Curve[i] * 255.0f + 0.5f)); break;
+          case icConvert16Bit:
+          case icConvertVariable:
+            arr.push_back((int)(m_Curve[i] * 65535.0f + 0.5f)); break;
+          default:
+            arr.push_back((double)m_Curve[i]); break;
+        }
       }
+      if (nType == icConvert8Bit)
+        j["precision"] = 1;
+      else if (nType == icConvert16Bit || nType == icConvertVariable)
+        j["precision"] = 2;
+      j["table"] = arr;
     }
-    if (nType == icConvert8Bit)
-      j["precision"] = 1;
-    else if (nType == icConvert16Bit || nType == icConvertVariable)
-      j["precision"] = 2;
-    j["table"] = arr;
   }
   return true;
 }
@@ -1418,7 +1454,15 @@ bool CIccTagJsonCurve::ParseJson(const IccJson &j, icConvertType /*nType*/, std:
   std::string curveType;
   if (!jGetString(j, "curveType", curveType)) return false;
   if (curveType == "identity") {
-    SetSize(0);
+    int size = 0;
+    jGetValue(j, "size", size);
+    if (size >= 2) {
+      if (!SetSize((icUInt32Number)size)) return false;
+      for (int i = 0; i < size; i++)
+        m_Curve[i] = (icFloatNumber)i / (icFloatNumber)(size - 1);
+    } else {
+      SetSize(0);
+    }
   } else if (curveType == "gamma") {
     SetSize(1);
     double gamma = 1.0;

@@ -234,6 +234,7 @@
       "required": ["curveType"],
       "properties": {
         "curveType": { "type": "string", "enum": ["identity", "gamma", "table"] },
+        "size":      { "type": "integer", "minimum": 2, "description": "Number of samples in a sampled-identity curve (when curveType is 'identity' and the curve has 2 or more entries). Omitted for the 0-entry ICC identity." },
         "gamma":     { "type": "number", "description": "Gamma exponent (when curveType is 'gamma')" },
         "precision": { "type": "integer", "enum": [1, 2], "description": "Table encoding: 1 = 8-bit integers (0–255), 2 = 16-bit integers (0–65535). Omitted for floating-point." },
         "table":     { "type": "array", "items": { "type": "number" }, "description": "Curve samples (when curveType is 'table'). Integers when precision is present, floats otherwise." }
@@ -343,14 +344,25 @@
       "description": "colorantTableType",
       "required": ["colorantTable"],
       "properties": {
+        "pcsEncoding": {
+          "type": "string",
+          "enum": ["Lab", "XYZ", "16bit"],
+          "description": "Encoding used for the 'pcs' arrays. 'Lab': L* (0–100), a*, b* (−128–127). 'XYZ': X, Y, Z floats (0–2 range). '16bit': raw ICC U16 integers. ToJson always writes 'Lab'; ParseJson defaults to 'Lab' when absent."
+        },
         "colorantTable": {
           "type": "array",
           "items": {
             "type": "object",
             "required": ["name", "pcs"],
             "properties": {
               "name": { "type": "string" },
-              "pcs":  { "$ref": "#/$defs/XYZTriplet" }
+              "pcs":  {
+                "type": "array",
+                "description": "PCS colorant coordinates. Interpretation depends on pcsEncoding.",
+                "items": { "type": "number" },
+                "minItems": 3,
+                "maxItems": 3
+              }
             }
           }
         }
@@ -567,6 +579,7 @@
       "properties": {
         "type": { "type": "string", "enum": ["Curve", "ParametricCurve", "SegmentedCurve"] },
         "curveType":      { "type": "string", "enum": ["identity", "gamma", "table"] },
+        "size":           { "type": "integer", "minimum": 2, "description": "Number of samples for a sampled-identity curve (when curveType is 'identity' and size >= 2)." },
         "gamma":          { "type": "number" },
         "precision":      { "type": "integer", "enum": [1, 2], "description": "Table encoding: 1 = 8-bit (0–255), 2 = 16-bit (0–65535). Omitted for float curves." },
         "table":          { "type": "array", "items": { "type": "number" }, "description": "Integers when precision present, floats otherwise." },

@@ -261,7 +261,7 @@ Each XYZ value is a JSON array `[X, Y, Z]`. The `"XYZ"` field is an array of suc
 
 The `"curveType"` field selects one of three subtypes: `"identity"`, `"gamma"`, or `"table"`.
 
-Identity (no-op):
+Identity (0-entry ICC no-op):
 ```json
 {
   "redTRCTag": {
@@ -270,6 +270,17 @@ Identity (no-op):
 }
 ```
 
+Sampled identity (linear ramp with a specific number of entries — emitted instead of a full table when all entries match the ramp `i/(n-1)` within 16-bit quantisation tolerance):
+```json
+{
+  "redTRCTag": {
+    "data": { "type": "curveType", "curveType": "identity", "size": 256 }
+  }
+}
+```
+
+When parsing, a `"size"` of 2 or more reconstructs the linear ramp `m_Curve[i] = i/(size-1)`. When `"size"` is absent the 0-entry ICC identity is used.
+
 Gamma:
 ```json
 {
@@ -354,6 +365,37 @@ Segment types:
 | `FormulaSegment`  | `functionType`, `parameters`  |
 | `SampledSegment`  | `samples`                     |
 
+### Colorant Tags
+
+#### `colorantTableType` — colorant names and PCS coordinates
+
+Because `ToJson`/`ParseJson` have no access to the profile header, the encoding of the `"pcs"` arrays is declared explicitly via a `"pcsEncoding"` field:
+
+| `pcsEncoding` | `pcs` array contents |
+|---------------|----------------------|
+| `"Lab"` (default) | L\* (0–100), a\*, b\* (−128–127) — human-readable CIE Lab |
+| `"XYZ"` | X, Y, Z floats (0–2 range) |
+| `"16bit"` | Raw ICC U16 integers (0–65535) |
+
+`ToJson` always writes `"pcsEncoding": "Lab"`. `ParseJson` defaults to `"Lab"` when the field is absent (backward compatible with files written before this field was added).
+
+```json
+{
+  "colorantTableTag": {
+    "data": {
+      "type": "colorantTableType",
+      "pcsEncoding": "Lab",
+      "colorantTable": [
+        { "name": "Cyan",    "pcs": [55.11, -37.40,  -5.18] },
+        { "name": "Magenta", "pcs": [48.24,  74.12, -49.52] },
+        { "name": "Yellow",  "pcs": [89.02,  -5.68,  93.14] },
+        { "name": "Black",   "pcs": [ 0.00,   0.00,   0.00] }
+      ]
+    }
+  }
+}
+```
+
 ### Signature Tags
 
 #### `signatureType`
@@ -428,7 +470,7 @@ MBB curve type values:
 
 | `type`           | Subtype fields                              |
 |------------------|---------------------------------------------|
-| `Curve`          | `curveType` (`"identity"`, `"gamma"`, `"table"`), `gamma`, `table` |
+| `Curve`          | `curveType` (`"identity"`, `"gamma"`, `"table"`), `size` (identity with entries), `gamma`, `table` |
 | `ParametricCurve`| `functionType`, `params`                    |
 | `SegmentedCurve` | `segments` array                            |