Cycles: support loading images from arbitrary OpenColorIO color space

These are the internal changes to Cycles, for Blender integration there are no
functional changes in this commit.

Images are converted to scene linear color space on file load, and on reading
from the OpenImageIO texture cache. 8-bit images are compressed with the sRGB
transfer function to avoid precision loss while keeping memory usages low. This
also means that for common cases of 8-bit sRGB images no conversion happens at
all on image loading.

Initial patch by Lukas, completed by Brecht.

Differential Revision: https://developer.blender.org/D3491

3 files changed, 30 insertions, 5 deletions

diff --git a/intern/cycles/blender/blender_mesh.cpp b/intern/cycles/blender/blender_mesh.cpp
index de594f4fb6c..1b47c4123e3 100644
--- a/intern/cycles/blender/blender_mesh.cpp
+++ b/intern/cycles/blender/blender_mesh.cpp
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#include "render/colorspace.h"
 #include "render/mesh.h"
 #include "render/object.h"
 #include "render/scene.h"
@@ -301,6 +302,7 @@ static void create_mesh_volume_attribute(
                                                INTERPOLATION_LINEAR,
                                                EXTENSION_CLIP,
                                                use_alpha,
+                                               u_colorspace_raw,
                                                metadata);
 }
 
diff --git a/intern/cycles/blender/blender_session.cpp b/intern/cycles/blender/blender_session.cpp
index 3a7e5f02b1d..c50dbb6ba55 100644
--- a/intern/cycles/blender/blender_session.cpp
+++ b/intern/cycles/blender/blender_session.cpp
@@ -16,12 +16,13 @@
 
 #include <stdlib.h>
 
+#include "device/device.h"
 #include "render/background.h"
 #include "render/buffers.h"
 #include "render/camera.h"
-#include "device/device.h"
-#include "render/integrator.h"
+#include "render/colorspace.h"
 #include "render/film.h"
+#include "render/integrator.h"
 #include "render/light.h"
 #include "render/mesh.h"
 #include "render/object.h"
@@ -1158,6 +1159,12 @@ void BlenderSession::builtin_image_info(const string &builtin_name,
     metadata.height = b_image.size()[1];
     metadata.depth = 1;
     metadata.channels = b_image.channels();
+
+    if (metadata.is_float) {
+      /* Float images are already converted on the Blender side,
+       * no need to do anything in Cycles. */
+      metadata.colorspace = u_colorspace_raw;
+    }
   }
   else if (b_id.is_a(&RNA_Object)) {
     /* smoke volume data */
diff --git a/intern/cycles/blender/blender_shader.cpp b/intern/cycles/blender/blender_shader.cpp
index d1f823bc2b8..e6ec8b22d7a 100644
--- a/intern/cycles/blender/blender_shader.cpp
+++ b/intern/cycles/blender/blender_shader.cpp
@@ -15,6 +15,7 @@
  */
 
 #include "render/background.h"
+#include "render/colorspace.h"
 #include "render/graph.h"
 #include "render/light.h"
 #include "render/nodes.h"
@@ -665,7 +666,14 @@ static ShaderNode *add_node(Scene *scene,
       }
 #endif
     }
-    image->color_space = (NodeImageColorSpace)b_image_node.color_space();
+    switch (b_image_node.color_space()) {
+      case BL::ShaderNodeTexImage::color_space_NONE:
+        image->colorspace = u_colorspace_raw;
+        break;
+      case BL::ShaderNodeTexImage::color_space_COLOR:
+        image->colorspace = u_colorspace_auto;
+        break;
+    }
     image->projection = (NodeImageProjection)b_image_node.projection();
     image->interpolation = get_image_interpolation(b_image_node);
     image->extension = get_image_extension(b_image_node);
@@ -710,7 +718,14 @@ static ShaderNode *add_node(Scene *scene,
       }
 #endif
     }
-    env->color_space = (NodeImageColorSpace)b_env_node.color_space();
+    switch (b_env_node.color_space()) {
+      case BL::ShaderNodeTexEnvironment::color_space_NONE:
+        env->colorspace = u_colorspace_raw;
+        break;
+      case BL::ShaderNodeTexEnvironment::color_space_COLOR:
+        env->colorspace = u_colorspace_auto;
+        break;
+    }
     env->interpolation = get_image_interpolation(b_env_node);
     env->projection = (NodeEnvironmentProjection)b_env_node.projection();
     BL::TexMapping b_texture_mapping(b_env_node.texture_mapping());
@@ -861,7 +876,8 @@ static ShaderNode *add_node(Scene *scene,
                                              point_density->builtin_data,
                                              point_density->interpolation,
                                              EXTENSION_CLIP,
-                                             true);
+                                             true,
+                                             u_colorspace_raw);
     }
     node = point_density;