diff --git a/src/encoder.rs b/src/encoder.rs
index 045a4aa..6c14c2b 100644
--- a/src/encoder.rs
+++ b/src/encoder.rs
@@ -4,6 +4,7 @@ use itertools::Itertools;
 use crate::common::*;
 
 // @TODO replace Options with custom Errors
+// @TODO encoder wrappers for RgbaImage/RgbImage
 
 impl Ops {
     fn write_encoded (self, buf: &mut Vec<u8>) {
@@ -42,7 +43,7 @@ fn encode_header (header: Header) -> Option<Vec<u8>> {
 fn encode_body (header: Header, data: &[u8]) -> Option<Vec<u8>> {
     let mut known = [[0u8; 4]; 64];
     let mut last = [0u8, 0, 0, 255];
-    let mut out = vec![];
+    let mut out = Vec::with_capacity(header.width as usize * header.height as usize);
     let mut cur = Ops::Nop;
 
     for mut chunk in &data.iter().chunks(header.channels.num()) {