diff --git a/assets/asset_builder/README.md b/assets/asset_builder/README.md
index 213a007..3e89837 100644
--- a/assets/asset_builder/README.md
+++ b/assets/asset_builder/README.md
@@ -2,15 +2,23 @@
 
 |    Description    |               Length                |
 | :---------------- | :---------------------------------- |
-| Assets number     | int (32 bits)                       |
+| Assets number     | size_t (64 bits)                    |
 | ...               |                                     |
 | Asset name        | const char * (variable length)      |
-| Asset start index | int (32 bits)                       |
-| Asset end index   | int (32 bits)                       |
+| Asset start index | size_t (64 bits)                    |
+| Asset end index   | size_t (64 bits)                    |
 | ...               |                                     |
 | Asset data        | depend on assets content and number |
 
 ## PNG
 
 Convert RGBA to RGB with #FF00FF as the transparent color.
-If alpha null then the color of the pixel will be replaced with this.
\ No newline at end of file
+If alpha null then the color of the pixel will be replaced with this.
+
+### Image asset data structure
+
+|    Description    |               Length                |
+| :---------------- | :---------------------------------- |
+| Image width       | size_t (64 bits)                    |
+| Image height      | size_t (64 bits)                    |
+| Image data        | depend on image content             |