diff --git a/imageflow_core/src/codecs/libpng_encoder.rs b/imageflow_core/src/codecs/libpng_encoder.rs
index b0d47579c..5fdddafeb 100644
--- a/imageflow_core/src/codecs/libpng_encoder.rs
+++ b/imageflow_core/src/codecs/libpng_encoder.rs
@@ -48,6 +48,10 @@ impl Encoder for LibPngEncoder {
                 bitmap.get_window_u8().unwrap()
                     .apply_matte(color.clone())
                     .map_err(|e| e.at(here!()))?;
+                // Optimize png size
+                if color.is_opaque(){
+                    bitmap.set_alpha_meaningful(false);
+                }
             }
         }
 
diff --git a/imageflow_core/src/codecs/mozjpeg.rs b/imageflow_core/src/codecs/mozjpeg.rs
index 548df0f5f..1790fe125 100644
--- a/imageflow_core/src/codecs/mozjpeg.rs
+++ b/imageflow_core/src/codecs/mozjpeg.rs
@@ -69,6 +69,7 @@ impl Encoder for MozjpegEncoder {
             .apply_matte(self.matte.clone().unwrap_or(
                 imageflow_types::Color::Srgb(imageflow_types::ColorSrgb::Hex("FFFFFFFF".to_owned()))))
             .map_err(|e| e.at(here!()))?;
+        bitmap.set_alpha_meaningful(false);
 
         let frame = unsafe{ bitmap.get_window_u8()
             .ok_or_else(|| nerror!(ErrorKind::InvalidBitmapType))?