diff --git a/in/1kb.qoi b/in/1kb.qoi
new file mode 100644
index 0000000..dd95fcc
Binary files /dev/null and b/in/1kb.qoi differ
diff --git a/out/1kb.qoi b/out/1kb.qoi
index da76eaa..e8925b8 100644
Binary files a/out/1kb.qoi and b/out/1kb.qoi differ
diff --git a/out/dice.qoi b/out/dice.qoi
index 2358313..9f6317c 100644
Binary files a/out/dice.qoi and b/out/dice.qoi differ
diff --git a/src/encoder.rs b/src/encoder.rs
index 3a1dbf7..7330596 100644
--- a/src/encoder.rs
+++ b/src/encoder.rs
@@ -9,17 +9,17 @@ impl Ops {
     // @TODO don't alloc here, get a mut reference and extend here
     fn format (self) -> Vec<u8> {
         // cast_diff
-        let cd = |diff: i8| cast_with_bias(diff, 2);
+        let cd = |diff: i8| cast_with_bias(diff, -2);
         // cast_luma_green
-        let clg = |diff: i8| cast_with_bias(diff, 32);
+        let clg = |diff: i8| cast_with_bias(diff, -32);
         // cast_luma_red_blue
-        let clrb = |diff: i8| cast_with_bias(diff, 8);
+        let clrb = |diff: i8| cast_with_bias(diff, -8);
 
         match self {
             Ops::Nop => vec![],
             Ops::Rgb([r, g, b]) => vec![254, r, g, b],
             Ops::Rgba([r, g, b, a]) => vec![255, r, g, b, a],
-            Ops::Index(idx) => vec![0b1111 & idx as u8],
+            Ops::Index(idx) => vec![idx as u8],
             Ops::Run(len) => vec![(3 << 6) | (len - 1)],
             Ops::Diff([dr, dg, db]) => vec![(1 << 6) | ((cd(dr) << 4) | (cd(dg) << 2) | cd(db)) ],
             Ops::Luma([dr, dg, db]) => vec![(2 << 6) | clg(dg), (clrb(dr) << 4) | clrb(db)],
@@ -75,7 +75,7 @@ fn encode_body (header: Header, data: &[u8]) -> Option<Vec<u8>> {
             // INDEX -> DIFF -> LUMA -> RGB(A)
             if known[hash] == rgba {
                 cur = Ops::Index(hash);
-            } else if let Some(ops) = diff_ops([r, g, b], [last[0], last[1], last[2]]) {
+            } else if let Some(ops) = diff_ops([last[0], last[1], last[2]], [r, g, b]) {
                 cur = ops;
             } else {
                 cur = header.channels.ops_color(&rgba[..header.channels.num()])?;
@@ -90,7 +90,7 @@ fn encode_body (header: Header, data: &[u8]) -> Option<Vec<u8>> {
 }
 
 
-fn encode_full (header: Header, bytes: &[u8]) -> Option<Vec<u8>> {
+pub fn encode_full (header: Header, bytes: &[u8]) -> Option<Vec<u8>> {
     let mut out = Vec::with_capacity(header.width as usize * header.height as usize * 4);
     out.extend_from_slice(&encode_header(header)?);
     out.extend_from_slice(&encode_body(header, bytes)?);
@@ -103,8 +103,6 @@ fn encode_full (header: Header, bytes: &[u8]) -> Option<Vec<u8>> {
 #[cfg(test)]
 mod test {
     use std::time::Instant;
-
-
     use super::*;
 
     #[test]