Cycles: Implement texture size limit simplify option

Main intention is to give some quick way to control scene's memory
usage by clamping textures which are too big. This is really handy
on the early production stages when you first create really nice
looking hi-res textures and only when it all works and approved
start investing time on optimizing your scene.

This is a new option in Scene Simplify panel and it acts as
following: when texture size is bigger than the given value it'll
be scaled down by half for until it fits into given limit.

There are various possible improvements, such as:

- Use threaded scaling using our own task manager.

  This is actually one of the main reasons why image resize is
  manually-implemented instead of using OIIO's resize. Other
  reason here is that API seems limited to construct 3D texture
  description easily.

- Vectorization of uchar4/float4/half4 textures.

- Use something smarter than box filter.

  Was playing with some other filters, but not sure they are
  really better: they kind of causes more fuzzy edges.

Even with such a TODOs in the code the option is already quite
useful.

Reviewers: brecht

Reviewed By: brecht

Subscribers: jtheninja, Blendify, gregzaal, venomgfx

Differential Revision: https://developer.blender.org/D2362

11 files changed, 365 insertions, 40 deletions

diff --git a/intern/cycles/blender/addon/properties.py b/intern/cycles/blender/addon/properties.py
index b53f85c3266..fed1524a816 100644
--- a/intern/cycles/blender/addon/properties.py
+++ b/intern/cycles/blender/addon/properties.py
@@ -129,6 +129,16 @@ enum_device_type = (
     ('OPENCL', "OpenCL", "OpenCL", 2)
     )
 
+enum_texture_limit = (
+    ('OFF', "No Limit", "No texture size limit", 0),
+    ('128', "128", "Limit texture size to 128 pixels", 1),
+    ('256', "256", "Limit texture size to 256 pixels", 2),
+    ('512', "512", "Limit texture size to 512 pixels", 3),
+    ('1024', "1024", "Limit texture size to 1024 pixels", 4),
+    ('2048', "2048", "Limit texture size to 2048 pixels", 5),
+    ('4096', "4096", "Limit texture size to 4096 pixels", 6),
+    ('8192', "8192", "Limit texture size to 8192 pixels", 7),
+    )
 
 class CyclesRenderSettings(bpy.types.PropertyGroup):
     @classmethod
@@ -608,6 +618,20 @@ class CyclesRenderSettings(bpy.types.PropertyGroup):
             min=0.0, max=1.0,
             )
 
+        cls.texture_limit = EnumProperty(
+            name="Viewport Texture Limit",
+            default='OFF',
+            description="Limit texture size used by viewport rendering",
+            items=enum_texture_limit
+            )
+
+        cls.texture_limit_render = EnumProperty(
+            name="Render Texture Limit",
+            default='OFF',
+            description="Limit texture size used by final rendering",
+            items=enum_texture_limit
+            )
+
         # Various fine-tuning debug flags
 
         def devices_update_callback(self, context):
diff --git a/intern/cycles/blender/addon/ui.py b/intern/cycles/blender/addon/ui.py
index 1856b278c89..3f7730efbb0 100644
--- a/intern/cycles/blender/addon/ui.py
+++ b/intern/cycles/blender/addon/ui.py
@@ -1587,29 +1587,40 @@ class CyclesScene_PT_simplify(CyclesButtonsPanel, Panel):
         cscene = scene.cycles
 
         layout.active = rd.use_simplify
-        split = layout.split()
 
-        col = split.column()
-        col.label(text="Viewport:")
-        col.prop(rd, "simplify_subdivision", text="Subdivision")
-        col.prop(rd, "simplify_child_particles", text="Child Particles")
+        col = layout.column(align=True)
+        col.label(text="Subdivision")
+        row = col.row(align=True)
+        row.prop(rd, "simplify_subdivision", text="Viewport")
+        row.prop(rd, "simplify_subdivision_render", text="Render")
 
-        col = split.column()
-        col.label(text="Render:")
-        col.prop(rd, "simplify_subdivision_render", text="Subdivision")
-        col.prop(rd, "simplify_child_particles_render", text="Child Particles")
+        col = layout.column(align=True)
+        col.label(text="Child Particles")
+        row = col.row(align=True)
+        row.prop(rd, "simplify_child_particles", text="Viewport")
+        row.prop(rd, "simplify_child_particles_render", text="Render")
 
-        layout.separator()
+        col = layout.column(align=True)
+        split = col.split()
+        sub = split.column()
+        sub.label(text="Texture Limit Viewport")
+        sub.prop(cscene, "texture_limit", text="")
+        sub = split.column()
+        sub.label(text="Texture Limit Render")
+        sub.prop(cscene, "texture_limit_render", text="")
 
         split = layout.split()
-
         col = split.column()
         col.prop(cscene, "use_camera_cull")
-        col.prop(cscene, "camera_cull_margin", text="Margin")
+        row = col.row()
+        row.active = cscene.use_camera_cull
+        row.prop(cscene, "camera_cull_margin")
 
         col = split.column()
         col.prop(cscene, "use_distance_cull")
-        col.prop(cscene, "distance_cull_margin", text="Distance")
+        row = col.row()
+        row.active = cscene.use_distance_cull
+        row.prop(cscene, "distance_cull_margin", text="Distance")
 
 def draw_device(self, context):
     scene = context.scene
diff --git a/intern/cycles/blender/blender_sync.cpp b/intern/cycles/blender/blender_sync.cpp
index 6118cc72239..38b2ce19e8a 100644
--- a/intern/cycles/blender/blender_sync.cpp
+++ b/intern/cycles/blender/blender_sync.cpp
@@ -504,6 +504,20 @@ SceneParams BlenderSync::get_scene_params(BL::Scene& b_scene,
 	else
 		params.persistent_data = false;
 
+	int texture_limit;
+	if(background) {
+		texture_limit = RNA_enum_get(&cscene, "texture_limit_render");
+	}
+	else {
+		texture_limit = RNA_enum_get(&cscene, "texture_limit");
+	}
+	if(texture_limit > 0 && b_scene.render().use_simplify()) {
+		params.texture_limit = 1 << (texture_limit + 6);
+	}
+	else {
+		params.texture_limit = 0;
+	}
+
 #if !(defined(__GNUC__) && (defined(i386) || defined(_M_IX86)))
 	if(is_cpu) {
 		params.use_qbvh = DebugFlags().cpu.qbvh && system_cpu_support_sse2();
diff --git a/intern/cycles/render/image.cpp b/intern/cycles/render/image.cpp
index 7465fbd43a7..11193bf4974 100644
--- a/intern/cycles/render/image.cpp
+++ b/intern/cycles/render/image.cpp
@@ -19,6 +19,7 @@
 #include "scene.h"
 
 #include "util_foreach.h"
+#include "util_logging.h"
 #include "util_path.h"
 #include "util_progress.h"
 #include "util_texture.h"
@@ -476,6 +477,7 @@ template<TypeDesc::BASETYPE FileFormat,
          typename DeviceType>
 bool ImageManager::file_load_image(Image *img,
                                    ImageDataType type,
+                                   int texture_limit,
                                    device_vector<DeviceType>& tex_img)
 {
 	const StorageType alpha_one = (FileFormat == TypeDesc::UINT8)? 255 : 1;
@@ -485,9 +487,15 @@ bool ImageManager::file_load_image(Image *img,
 		return false;
 	}
 	/* Read RGBA pixels. */
-	StorageType *pixels = (StorageType*)tex_img.resize(width, height, depth);
-	if(pixels == NULL) {
-		return false;
+	vector<StorageType> pixels_storage;
+	StorageType *pixels;
+	const size_t max_size = max(max(width, height), depth);
+	if(texture_limit > 0 && max_size > texture_limit) {
+		pixels_storage.resize(((size_t)width)*height*depth*4);
+		pixels = &pixels_storage[0];
+	}
+	else {
+		pixels = (StorageType*)tex_img.resize(width, height, depth);
 	}
 	bool cmyk = false;
 	if(in) {
@@ -526,12 +534,12 @@ bool ImageManager::file_load_image(Image *img,
 		if(FileFormat == TypeDesc::FLOAT) {
 			builtin_image_float_pixels_cb(img->filename,
 			                              img->builtin_data,
-			                              (float*)pixels);
+			                              (float*)&pixels[0]);
 		}
 		else if(FileFormat == TypeDesc::UINT8) {
 			builtin_image_pixels_cb(img->filename,
 			                        img->builtin_data,
-			                        (uchar*)pixels);
+			                        (uchar*)&pixels[0]);
 		}
 		else {
 			/* TODO(dingto): Support half for ImBuf. */
@@ -540,10 +548,10 @@ bool ImageManager::file_load_image(Image *img,
 	/* Check if we actually have a float4 slot, in case components == 1,
 	 * but device doesn't support single channel textures.
 	 */
-	if(type == IMAGE_DATA_TYPE_FLOAT4 ||
-	   type == IMAGE_DATA_TYPE_HALF4 ||
-	   type == IMAGE_DATA_TYPE_BYTE4)
-	{
+	bool is_rgba = (type == IMAGE_DATA_TYPE_FLOAT4 ||
+	                type == IMAGE_DATA_TYPE_HALF4 ||
+	                type == IMAGE_DATA_TYPE_BYTE4);
+	if(is_rgba) {
 		size_t num_pixels = ((size_t)width) * height * depth;
 		if(cmyk) {
 			/* CMYK */
@@ -587,14 +595,41 @@ bool ImageManager::file_load_image(Image *img,
 			}
 		}
 	}
+	if(pixels_storage.size() > 0) {
+		float scale_factor = 1.0f;
+		while(max_size * scale_factor > texture_limit) {
+			scale_factor *= 0.5f;
+		}
+		VLOG(1) << "Scaling image " << img->filename
+		        << " by a factor of " << scale_factor << ".";
+		vector<StorageType> scaled_pixels;
+		size_t scaled_width, scaled_height, scaled_depth;
+		util_image_resize_pixels(pixels_storage,
+		                         width, height, depth,
+		                         is_rgba ? 4 : 1,
+		                         scale_factor,
+		                         &scaled_pixels,
+		                         &scaled_width, &scaled_height, &scaled_depth);
+		StorageType *texture_pixels = (StorageType*)tex_img.resize(scaled_width,
+		                                                           scaled_height,
+		                                                           scaled_depth);
+		memcpy(texture_pixels,
+		       &scaled_pixels[0],
+		       scaled_pixels.size() * sizeof(StorageType));
+	}
 	return true;
 }
 
-void ImageManager::device_load_image(Device *device, DeviceScene *dscene, ImageDataType type, int slot, Progress *progress)
+void ImageManager::device_load_image(Device *device,
+                                     DeviceScene *dscene,
+                                     Scene *scene,
+                                     ImageDataType type,
+                                     int slot,
+                                     Progress *progress)
 {
 	if(progress->get_cancel())
 		return;
-	
+
 	Image *img = images[type][slot];
 
 	if(osl_texture_system && !img->builtin_data)
@@ -603,6 +638,8 @@ void ImageManager::device_load_image(Device *device, DeviceScene *dscene, ImageD
 	string filename = path_filename(images[type][slot]->filename);
 	progress->set_status("Updating Images", "Loading " + filename);
 
+	const int texture_limit = scene->params.texture_limit;
+
 	/* Slot assignment */
 	int flat_slot = type_index_to_flattened_slot(slot, type);
 
@@ -622,7 +659,11 @@ void ImageManager::device_load_image(Device *device, DeviceScene *dscene, ImageD
 			device->tex_free(tex_img);
 		}
 
-		if(!file_load_image<TypeDesc::FLOAT, float>(img, type, tex_img)) {
+		if(!file_load_image<TypeDesc::FLOAT, float>(img,
+		                                            type,
+		                                            texture_limit,
+		                                            tex_img))
+		{
 			/* on failure to load, we set a 1x1 pixels pink image */
 			float *pixels = (float*)tex_img.resize(1, 1);
 
@@ -648,7 +689,11 @@ void ImageManager::device_load_image(Device *device, DeviceScene *dscene, ImageD
 			device->tex_free(tex_img);
 		}
 
-		if(!file_load_image<TypeDesc::FLOAT, float>(img, type, tex_img)) {
+		if(!file_load_image<TypeDesc::FLOAT, float>(img,
+		                                            type,
+		                                            texture_limit,
+		                                            tex_img))
+		{
 			/* on failure to load, we set a 1x1 pixels pink image */
 			float *pixels = (float*)tex_img.resize(1, 1);
 
@@ -671,7 +716,11 @@ void ImageManager::device_load_image(Device *device, DeviceScene *dscene, ImageD
 			device->tex_free(tex_img);
 		}
 
-		if(!file_load_image<TypeDesc::UINT8, uchar>(img, type, tex_img)) {
+		if(!file_load_image<TypeDesc::UINT8, uchar>(img,
+		                                            type,
+		                                            texture_limit,
+		                                            tex_img))
+		{
 			/* on failure to load, we set a 1x1 pixels pink image */
 			uchar *pixels = (uchar*)tex_img.resize(1, 1);
 
@@ -697,7 +746,10 @@ void ImageManager::device_load_image(Device *device, DeviceScene *dscene, ImageD
 			device->tex_free(tex_img);
 		}
 
-		if(!file_load_image<TypeDesc::UINT8, uchar>(img, type, tex_img)) {
+		if(!file_load_image<TypeDesc::UINT8, uchar>(img,
+		                                            type,
+		                                            texture_limit,
+		                                            tex_img)) {
 			/* on failure to load, we set a 1x1 pixels pink image */
 			uchar *pixels = (uchar*)tex_img.resize(1, 1);
 
@@ -720,7 +772,10 @@ void ImageManager::device_load_image(Device *device, DeviceScene *dscene, ImageD
 			device->tex_free(tex_img);
 		}
 
-		if(!file_load_image<TypeDesc::HALF, half>(img, type, tex_img)) {
+		if(!file_load_image<TypeDesc::HALF, half>(img,
+		                                          type,
+		                                          texture_limit,
+		                                          tex_img)) {
 			/* on failure to load, we set a 1x1 pixels pink image */
 			half *pixels = (half*)tex_img.resize(1, 1);
 
@@ -746,7 +801,10 @@ void ImageManager::device_load_image(Device *device, DeviceScene *dscene, ImageD
 			device->tex_free(tex_img);
 		}
 
-		if(!file_load_image<TypeDesc::HALF, half>(img, type, tex_img)) {
+		if(!file_load_image<TypeDesc::HALF, half>(img,
+		                                          type,
+		                                          texture_limit,
+		                                          tex_img)) {
 			/* on failure to load, we set a 1x1 pixels pink image */
 			half *pixels = (half*)tex_img.resize(1, 1);
 
@@ -842,7 +900,10 @@ void ImageManager::device_free_image(Device *device, DeviceScene *dscene, ImageD
 	}
 }
 
-void ImageManager::device_update(Device *device, DeviceScene *dscene, Progress& progress)
+void ImageManager::device_update(Device *device,
+                                 DeviceScene *dscene,
+                                 Scene *scene,
+                                 Progress& progress)
 {
 	if(!need_update)
 		return;
@@ -859,7 +920,14 @@ void ImageManager::device_update(Device *device, DeviceScene *dscene, Progress&
 			}
 			else if(images[type][slot]->need_load) {
 				if(!osl_texture_system || images[type][slot]->builtin_data)
-					pool.push(function_bind(&ImageManager::device_load_image, this, device, dscene, (ImageDataType)type, slot, &progress));
+					pool.push(function_bind(&ImageManager::device_load_image,
+					                        this,
+					                        device,
+					                        dscene,
+					                        scene,
+					                        (ImageDataType)type,
+					                        slot,
+					                        &progress));
 			}
 		}
 	}
@@ -874,6 +942,7 @@ void ImageManager::device_update(Device *device, DeviceScene *dscene, Progress&
 
 void ImageManager::device_update_slot(Device *device,
                                       DeviceScene *dscene,
+                                      Scene *scene,
                                       int flat_slot,
                                       Progress *progress)
 {
@@ -890,6 +959,7 @@ void ImageManager::device_update_slot(Device *device,
 		if(!osl_texture_system || image->builtin_data)
 			device_load_image(device,
 			                  dscene,
+			                  scene,
 			                  type,
 			                  slot,
 			                  progress);
diff --git a/intern/cycles/render/image.h b/intern/cycles/render/image.h
index 1dc4bf180f8..3da7338985c 100644
--- a/intern/cycles/render/image.h
+++ b/intern/cycles/render/image.h
@@ -30,6 +30,7 @@ CCL_NAMESPACE_BEGIN
 class Device;
 class DeviceScene;
 class Progress;
+class Scene;
 
 class ImageManager {
 public:
@@ -67,8 +68,15 @@ public:
 	                      ExtensionType extension);
 	ImageDataType get_image_metadata(const string& filename, void *builtin_data, bool& is_linear);
 
-	void device_update(Device *device, DeviceScene *dscene, Progress& progress);
-	void device_update_slot(Device *device, DeviceScene *dscene, int flat_slot, Progress *progress);
+	void device_update(Device *device,
+	                   DeviceScene *dscene,
+	                   Scene *scene,
+	                   Progress& progress);
+	void device_update_slot(Device *device,
+	                        DeviceScene *dscene,
+	                        Scene *scene,
+	                        int flat_slot,
+	                        Progress *progress);
 	void device_free(Device *device, DeviceScene *dscene);
 	void device_free_builtin(Device *device, DeviceScene *dscene);
 
@@ -114,6 +122,7 @@ private:
 	         typename DeviceType>
 	bool file_load_image(Image *img,
 	                     ImageDataType type,
+	                     int texture_limit,
 	                     device_vector<DeviceType>& tex_img);
 
 	int type_index_to_flattened_slot(int slot, ImageDataType type);
@@ -122,10 +131,20 @@ private:
 
 	uint8_t pack_image_options(ImageDataType type, size_t slot);
 
-	void device_load_image(Device *device, DeviceScene *dscene, ImageDataType type, int slot, Progress *progess);
-	void device_free_image(Device *device, DeviceScene *dscene, ImageDataType type, int slot);
-
-	void device_pack_images(Device *device, DeviceScene *dscene, Progress& progess);
+	void device_load_image(Device *device,
+	                       DeviceScene *dscene,
+	                       Scene *scene,
+	                       ImageDataType type,
+	                       int slot,
+	                       Progress *progess);
+	void device_free_image(Device *device,
+	                       DeviceScene *dscene,
+	                       ImageDataType type,
+	                       int slot);
+
+	void device_pack_images(Device *device,
+	                        DeviceScene *dscene,
+	                        Progress& progess);
 };
 
 CCL_NAMESPACE_END
diff --git a/intern/cycles/render/mesh.cpp b/intern/cycles/render/mesh.cpp
index 32dba532f2b..df4327d021a 100644
--- a/intern/cycles/render/mesh.cpp
+++ b/intern/cycles/render/mesh.cpp
@@ -1665,6 +1665,7 @@ void MeshManager::device_update_displacement_images(Device *device,
 						 */
 						image_manager->device_update(device,
 						                             dscene,
+						                             scene,
 						                             progress);
 						return;
 					}
@@ -1682,6 +1683,7 @@ void MeshManager::device_update_displacement_images(Device *device,
 		                        image_manager,
 		                        device,
 		                        dscene,
+		                        scene,
 		                        slot,
 		                        &progress));
 	}
diff --git a/intern/cycles/render/scene.cpp b/intern/cycles/render/scene.cpp
index b341837b7e8..68124e78cb5 100644
--- a/intern/cycles/render/scene.cpp
+++ b/intern/cycles/render/scene.cpp
@@ -187,7 +187,7 @@ void Scene::device_update(Device *device_, Progress& progress)
 	if(progress.get_cancel() || device->have_error()) return;
 
 	progress.set_status("Updating Images");
-	image_manager->device_update(device, &dscene, progress);
+	image_manager->device_update(device, &dscene, this, progress);
 
 	if(progress.get_cancel() || device->have_error()) return;
 
diff --git a/intern/cycles/render/scene.h b/intern/cycles/render/scene.h
index 8fec171b6fb..df9363cc768 100644
--- a/intern/cycles/render/scene.h
+++ b/intern/cycles/render/scene.h
@@ -145,6 +145,7 @@ public:
 	bool use_bvh_unaligned_nodes;
 	bool use_qbvh;
 	bool persistent_data;
+	int texture_limit;
 
 	SceneParams()
 	{
@@ -154,6 +155,7 @@ public:
 		use_bvh_unaligned_nodes = true;
 		use_qbvh = false;
 		persistent_data = false;
+		texture_limit = 0;
 	}
 
 	bool modified(const SceneParams& params)
@@ -162,7 +164,8 @@ public:
 		&& use_bvh_spatial_split == params.use_bvh_spatial_split
 		&& use_bvh_unaligned_nodes == params.use_bvh_unaligned_nodes
 		&& use_qbvh == params.use_qbvh
-		&& persistent_data == params.persistent_data); }
+		&& persistent_data == params.persistent_data
+		&& texture_limit == params.texture_limit); }
 };
 
 /* Scene */
diff --git a/intern/cycles/util/CMakeLists.txt b/intern/cycles/util/CMakeLists.txt
index 02ee4cd6774..d8abf671bd6 100644
--- a/intern/cycles/util/CMakeLists.txt
+++ b/intern/cycles/util/CMakeLists.txt
@@ -45,6 +45,7 @@ set(SRC_HEADERS
 	util_half.h
 	util_hash.h
 	util_image.h
+	util_image_impl.h
 	util_list.h
 	util_logging.h
 	util_map.h
diff --git a/intern/cycles/util/util_image.h b/intern/cycles/util/util_image.h
index bb8a31c6fec..c8efc551d97 100644
--- a/intern/cycles/util/util_image.h
+++ b/intern/cycles/util/util_image.h
@@ -21,11 +21,25 @@
 
 #include <OpenImageIO/imageio.h>
 
+#include "util_vector.h"
+
 CCL_NAMESPACE_BEGIN
 
 OIIO_NAMESPACE_USING
 
+template<typename T>
+void util_image_resize_pixels(const vector<T>& input_pixels,
+                              const size_t input_width,
+                              const size_t input_height,
+                              const size_t input_depth,
+                              const size_t components,
+                              vector<T> *output_pixels,
+                              size_t *output_width,
+                              size_t *output_height,
+                              size_t *output_depth);
+
 CCL_NAMESPACE_END
 
 #endif /* __UTIL_IMAGE_H__ */
 
+#include "util_image_impl.h"
diff --git a/intern/cycles/util/util_image_impl.h b/intern/cycles/util/util_image_impl.h
new file mode 100644
index 00000000000..3429ee46e94
--- /dev/null
+++ b/intern/cycles/util/util_image_impl.h
@@ -0,0 +1,167 @@
+/*
+ * Copyright 2011-2016 Blender Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __UTIL_IMAGE_IMPL_H__
+#define __UTIL_IMAGE_IMPL_H__
+
+#include "util_debug.h"
+#include "util_image.h"
+
+CCL_NAMESPACE_BEGIN
+
+namespace {
+
+template<typename T>
+const T *util_image_read(const vector<T>& pixels,
+                         const size_t width,
+                         const size_t height,
+                         const size_t /*depth*/,
+                         const size_t components,
+                         const size_t x, const size_t y, const size_t z) {
+	const size_t index = ((size_t)z * (width * height) +
+	                      (size_t)y * width +
+	                      (size_t)x) * components;
+	return &pixels[index];
+}
+
+template<typename T>
+void util_image_downscale_sample(const vector<T>& pixels,
+                                 const size_t width,
+                                 const size_t height,
+                                 const size_t depth,
+                                 const size_t components,
+                                 const size_t kernel_size,
+                                 const float x,
+                                 const float y,
+                                 const float z,
+                                 T *result)
+{
+	assert(components <= 4);
+	const size_t ix = (size_t)x,
+	             iy = (size_t)y,
+	             iz = (size_t)z;
+	/* TODO(sergey): Support something smarter than box filer. */
+	float accum[4] = {0};
+	size_t count = 0;
+	for(size_t dz = 0; dz < kernel_size; ++dz) {
+		for(size_t dy = 0; dy < kernel_size; ++dy) {
+			for(size_t dx = 0; dx < kernel_size; ++dx) {
+				const size_t nx = ix + dx,
+				             ny = iy + dy,
+				             nz = iz + dz;
+				if(nx >= width || ny >= height || nz >= depth) {
+					continue;
+				}
+				const T *pixel = util_image_read(pixels,
+				                                 width, height, depth,
+				                                 components,
+				                                 nx, ny, nz);
+				for(size_t k = 0; k < components; ++k) {
+					accum[k] += pixel[k];
+				}
+				++count;
+			}
+		}
+	}
+	const float inv_count = 1.0f / (float)count;
+	for(size_t k = 0; k < components; ++k) {
+		result[k] = T(accum[k] * inv_count);
+	}
+}
+
+template<typename T>
+void util_image_downscale_pixels(const vector<T>& input_pixels,
+                                 const size_t input_width,
+                                 const size_t input_height,
+                                 const size_t input_depth,
+                                 const size_t components,
+                                 const float inv_scale_factor,
+                                 const size_t output_width,
+                                 const size_t output_height,
+                                 const size_t output_depth,
+                                 vector<T> *output_pixels)
+{
+	const size_t kernel_size = (size_t)(inv_scale_factor + 0.5f);
+	for(size_t z = 0; z < output_depth; ++z) {
+		for(size_t y = 0; y < output_height; ++y) {
+			for(size_t x = 0; x < output_width; ++x) {
+				const float input_x = (float)x * inv_scale_factor,
+				            input_y = (float)y * inv_scale_factor,
+				            input_z = (float)z * inv_scale_factor;
+				const size_t output_index =
+				        (z * output_width * output_height +
+				         y * output_width + x) * components;
+				util_image_downscale_sample(input_pixels,
+				                            input_width, input_height, input_depth,
+				                            components,
+				                            kernel_size,
+				                            input_x, input_y, input_z,
+				                            &output_pixels->at(output_index));
+			}
+		}
+	}
+}
+
+}  /* namespace */
+
+template<typename T>
+void util_image_resize_pixels(const vector<T>& input_pixels,
+                              const size_t input_width,
+                              const size_t input_height,
+                              const size_t input_depth,
+                              const size_t components,
+                              const float scale_factor,
+                              vector<T> *output_pixels,
+                              size_t *output_width,
+                              size_t *output_height,
+                              size_t *output_depth)
+{
+	/* Early output for case when no scaling is applied. */
+	if(scale_factor == 1.0f) {
+		*output_width = input_width;
+		*output_height = input_height;
+		*output_depth = input_depth;
+		*output_pixels = input_pixels;
+		return;
+	}
+	/* First of all, we calculate output image dimensions.
+	 * We clamp them to be 1 pixel at least so we do not generate degenerate
+	 * image.
+	 */
+	*output_width = max((size_t)((float)input_width * scale_factor), 1);
+	*output_height = max((size_t)((float)input_height * scale_factor), 1);
+	*output_depth = max((size_t)((float)input_depth * scale_factor), 1);
+	/* Prepare pixel storage for the result. */
+	const size_t num_output_pixels = ((*output_width) *
+	                                  (*output_height) *
+	                                  (*output_depth)) * components;
+	output_pixels->resize(num_output_pixels);
+	if(scale_factor < 1.0f) {
+		const float inv_scale_factor = 1.0f / scale_factor;
+		util_image_downscale_pixels(input_pixels,
+		                            input_width, input_height, input_depth,
+		                            components,
+		                            inv_scale_factor,
+		                            *output_width, *output_height, *output_depth,
+		                            output_pixels);
+	} else {
+		/* TODO(sergey): Needs implementation. */
+	}
+}
+
+CCL_NAMESPACE_END
+
+#endif  /* __UTIL_IMAGE_IMPL_H__ */