diff --git a/src/doc/CMakeLists.txt b/src/doc/CMakeLists.txt
index d1c5973d1..2b2f5492a 100644
--- a/src/doc/CMakeLists.txt
+++ b/src/doc/CMakeLists.txt
@@ -1,4 +1,5 @@
 # Aseprite Document Library
+# Copyright (C) 2020 Igara Studio S.A.
 # Copyright (C) 2001-2018 David Capello
 
 if(WIN32)
@@ -28,6 +29,7 @@ add_library(doc-lib
   cel_data_io.cpp
   cel_io.cpp
   cels_range.cpp
+  color.cpp
   compressed_image.cpp
   conversion_to_surface.cpp
   document.cpp
diff --git a/src/doc/color.cpp b/src/doc/color.cpp
new file mode 100644
index 000000000..470d71b90
--- /dev/null
+++ b/src/doc/color.cpp
@@ -0,0 +1,46 @@
+// Aseprite Document Library
+// Copyright (c) 2020 Igara Studio S.A.
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "doc/color.h"
+
+#include <algorithm>
+
+namespace doc {
+
+color_t rgba_to_graya_using_hsv(const color_t c)
+{
+  const uint8_t M = std::max(rgba_getr(c),
+                             std::max(rgba_getg(c),
+                                      rgba_getb(c)));
+  return graya(M,
+               rgba_geta(c));
+}
+
+color_t rgba_to_graya_using_hsl(const color_t c)
+{
+  const int m = std::min(rgba_getr(c),
+                         std::min(rgba_getg(c),
+                                  rgba_getb(c)));
+  const int M = std::max(rgba_getr(c),
+                         std::max(rgba_getg(c),
+                                  rgba_getb(c)));
+  return graya((M + m) / 2,
+               rgba_geta(c));
+}
+
+color_t rgba_to_graya_using_luma(const color_t c)
+{
+  return graya(rgb_luma(rgba_getr(c),
+                        rgba_getg(c),
+                        rgba_getb(c)),
+               rgba_geta(c));
+}
+
+} // namespace doc
diff --git a/src/doc/color.h b/src/doc/color.h
index 20b04608d..ac65b0034 100644
--- a/src/doc/color.h
+++ b/src/doc/color.h
@@ -11,8 +11,6 @@
 
 #include "base/ints.h"
 
-#include <algorithm>
-
 namespace doc {
 
   // The greatest int type to storage a color for an image in the
@@ -95,31 +93,9 @@ namespace doc {
 
   typedef color_t (*rgba_to_graya_func)(const color_t c);
 
-  inline color_t rgba_to_graya_using_hsv(const color_t c) {
-    const uint8_t M = std::max(rgba_getr(c),
-                               std::max(rgba_getg(c),
-                                        rgba_getb(c)));
-    return graya(M,
-                 rgba_geta(c));
-  }
-
-  inline color_t rgba_to_graya_using_hsl(const color_t c) {
-    const int m = std::min(rgba_getr(c),
-                           std::min(rgba_getg(c),
-                                    rgba_getb(c)));
-    const int M = std::max(rgba_getr(c),
-                           std::max(rgba_getg(c),
-                                    rgba_getb(c)));
-    return graya((M + m) / 2,
-                 rgba_geta(c));
-  }
-
-  inline color_t rgba_to_graya_using_luma(const color_t c) {
-    return graya(rgb_luma(rgba_getr(c),
-                          rgba_getg(c),
-                          rgba_getb(c)),
-                 rgba_geta(c));
-  }
+  color_t rgba_to_graya_using_hsv(const color_t c);
+  color_t rgba_to_graya_using_hsl(const color_t c);
+  color_t rgba_to_graya_using_luma(const color_t c);
 
 } // namespace doc