diff --git a/Cargo.toml b/Cargo.toml
index caf9afa..b4d0742 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -13,7 +13,6 @@ crate-type = ["cdylib"]
 [dependencies]
 "base64" = "^0.12.3"
 "bitsy-parser" = "^0.72.3"
-"dither" = "1.3.9"
 "image" = "^0.23.7"
 "json" = "^0.12.4"
 "lazy_static" = "^1.4.0"
diff --git a/TODO.md b/TODO.md
index d0fd61a..bafbfbf 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,8 +1,7 @@
 # todo
 
-* preview
-* dithering
 * tests
 * if image is exactly 128×128, *don't* crop
 * custom palette
 * tile reuse
+* find a way to implement Atkinson dithering instead of CatmullRom
diff --git a/src/colour_map.rs b/src/colour_map.rs
new file mode 100644
index 0000000..1a0b62e
--- /dev/null
+++ b/src/colour_map.rs
@@ -0,0 +1,74 @@
+use image::{Luma, Rgba};
+
+#[derive(Clone, Copy)]
+pub struct ColourMap {
+    background: Rgba<u8>,
+    foreground: Rgba<u8>,
+}
+
+impl ColourMap {
+    pub(crate) fn from(palette: &bitsy_parser::Palette) -> ColourMap {
+        let background = Rgba::from([
+            palette.colours[0].red,
+            palette.colours[0].green,
+            palette.colours[0].blue,
+            255,
+        ]);
+
+        let foreground = Rgba::from([
+            palette.colours[1].red,
+            palette.colours[1].green,
+            palette.colours[1].blue,
+            255,
+        ]);
+
+        ColourMap { background, foreground }
+    }
+}
+
+fn diff(a: &Rgba<u8>, b:&Rgba<u8>) -> u32 {
+    let diff_red  = (a[0] as i16 - b[0] as i16).abs();
+    let diff_green= (a[1] as i16 - b[1] as i16).abs();
+    let diff_blue = (a[2] as i16 - b[2] as i16).abs();
+
+    (diff_red + diff_green + diff_blue) as u32
+}
+
+impl image::imageops::colorops::ColorMap for ColourMap {
+    type Color = Rgba<u8>;
+
+    #[inline(always)]
+    fn index_of(&self, color: &Self::Color) -> usize {
+        let diff_background = diff(color, &self.background);
+        let diff_foreground = diff(color, &self.foreground);
+
+        if diff_foreground <= diff_background { 1 } else { 0 }
+    }
+
+    #[inline(always)]
+    fn lookup(&self, idx: usize) -> Option<Self::Color> {
+        match idx {
+            0 => Some(self.background.into()),
+            1 => Some(self.foreground.into()),
+            _ => None,
+        }
+    }
+
+    /// Indicate NeuQuant implements `lookup`.
+    fn has_lookup(&self) -> bool {
+        true
+    }
+
+    #[inline(always)]
+    fn map_color(&self, color: &mut Self::Color) {
+        let closest = match self.index_of(color) {
+            1 => self.foreground,
+            _ => self.background,
+        };
+
+        color[0] = closest[0];
+        color[1] = closest[1];
+        color[2] = closest[2];
+        color[3] = closest[3];
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 1268165..173a2eb 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,11 +3,15 @@
 use bitsy_parser::game::Game;
 use bitsy_parser::image::Image;
 use bitsy_parser::tile::Tile;
-use image::{GenericImageView, Pixel, DynamicImage};
+use image::{GenericImageView, Pixel, DynamicImage, GenericImage, ImageBuffer};
 use lazy_static::lazy_static;
 use std::sync::Mutex;
 use wasm_bindgen::prelude::*;
-use image::imageops::dither;
+
+mod colour_map;
+
+use colour_map::ColourMap;
+use image::imageops::FilterType::CatmullRom;
 
 const SD: u32 = 8;
 
@@ -156,54 +160,21 @@ fn image_to_base64(image: &DynamicImage) -> String {
     format!("data:image/png;base64,{}", base64::encode(&bytes))
 }
 
-fn colour_difference(compare: image::Rgba<u8>, other: &bitsy_parser::Colour) -> u32 {
-    let diff_red  = (compare[0] as i16 - other.red   as i16).abs();
-    let diff_green= (compare[1] as i16 - other.green as i16).abs();
-    let diff_blue = (compare[2] as i16 - other.blue  as i16).abs();
-
-    (diff_red + diff_green + diff_blue) as u32
-}
-
-fn closest_colour(compare: image::Rgba<u8>, colours: &[bitsy_parser::Colour]) -> image::Rgba<u8> {
-    let diff_background = colour_difference(compare, &colours[0]);
-    let diff_foreground = colour_difference(compare, &colours[1]);
-
-    if diff_foreground <= diff_background {
-        image::Rgba::from([colours[1].red, colours[1].green, colours[1].blue, 255])
-    } else {
-        image::Rgba::from([colours[0].red, colours[0].green, colours[0].blue, 255])
-    }
-}
-
-fn adjust_brightness(pixel: &mut image::Rgba<u8>, state: &State) -> image::Rgba<u8> {
-    pixel[0] = (pixel[0] as i32 + state.brightness).clamp(0, 255) as u8;
-    pixel[1] = (pixel[1] as i32 + state.brightness).clamp(0, 255) as u8;
-    pixel[2] = (pixel[2] as i32 + state.brightness).clamp(0, 255) as u8;
-
-    *pixel
-}
-
 fn render_preview(state: &State) -> DynamicImage {
-    let image = state.image.as_ref().unwrap().clone();
-    let mut preview = image.clone();
+    let mut buffer =  state.image.as_ref().unwrap().clone().into_rgba();
 
-    // todo dither
+    // todo get actual chosen palette
+    let colour_map = crate::ColourMap::from(&state.game.as_ref().unwrap().palettes[0]);
 
-    // todo convert to palette colours
+    image::imageops::brighten(&mut buffer, state.brightness);
 
-    // get background and foreground colours from palette
-    let colours = &state.game.as_ref().unwrap().palettes
-        .iter()
-        .find(|palette| &palette.id == state.palette.as_ref().unwrap())
-        .unwrap()
-        .colours[0..2];
-
-    for (x, y, mut pixel) in image.pixels() {
-        // is pixel closer to background or foreground?
-        preview.put_pixel(x, y, closest_colour(adjust_brightness(&mut pixel, &state), colours));
+    if state.dither {
+        image::imageops::dither(&mut buffer, &colour_map);
+    } else {
+        image::imageops::colorops::index_colors(&mut buffer, &colour_map);
     }
 
-    preview
+    image::DynamicImage::ImageRgba8(buffer)
 }
 
 #[wasm_bindgen]