diff --git a/cli/index.js b/cli/index.js
index 3e871232..7fa64ac5 100644
--- a/cli/index.js
+++ b/cli/index.js
@@ -24,10 +24,16 @@ async function optimize(bitmapIn, encode, decode) {
   let bitmapOut;
   let binaryOut;
 
-  const { visdif } = await visdifModule();
+  const { VisDiff } = await visdifModule();
+  const comparator = new VisDiff(
+    bitmapIn.data,
+    bitmapIn.width,
+    bitmapIn.height
+  );
   do {
     binaryOut = await encode(bitmapIn, quality);
     bitmapOut = await decode(binaryOut);
+    butteraugliDistance = comparator.distance(bitmapOut.data);
     console.log({
       butteraugliDistance,
       quality,
@@ -35,12 +41,6 @@ async function optimize(bitmapIn, encode, decode) {
       binaryOut,
       bitmapOut
     });
-    butteraugliDistance = visdif(
-      bitmapIn.data,
-      bitmapOut.data,
-      bitmapIn.width,
-      bitmapIn.height
-    );
     if (butteraugliDistance > butteraugliGoal) {
       quality += inc;
     } else {
@@ -53,6 +53,8 @@ async function optimize(bitmapIn, encode, decode) {
     attempts < maxRounds
   );
 
+  comparator.delete();
+
   return {
     bitmap: bitmapOut,
     binary: binaryOut,
diff --git a/codecs/visdif/visdif.cpp b/codecs/visdif/visdif.cpp
index 7f2608a3..a13e5e31 100644
--- a/codecs/visdif/visdif.cpp
+++ b/codecs/visdif/visdif.cpp
@@ -5,50 +5,57 @@
 using namespace emscripten;
 using namespace butteraugli;
 
-double visdif(std::string rgba1, std::string rgba2, int width, int height) {
-  const char* rgba1p = rgba1.c_str();
-  const char* rgba2p = rgba2.c_str();
-  // One Image8 for each color channel + alpha
-  std::vector<ImageF> img1;
-  img1.push_back(ImageF(width, height));
-  img1.push_back(ImageF(width, height));
-  img1.push_back(ImageF(width, height));
-  img1.push_back(ImageF(width, height));
-  std::vector<ImageF> img2;
-  img2.push_back(ImageF(width, height));
-  img2.push_back(ImageF(width, height));
-  img2.push_back(ImageF(width, height));
-  img2.push_back(ImageF(width, height));
-  // Convert from interleaved RGBA to separate channels
+// Turns an interleaved RGBA buffer into 4 planes for each color channel
+void planarize(std::vector<ImageF>& img,
+               const char* rgba,
+               int width,
+               int height,
+               float gamma = 2.2) {
+  assert(img.size() == 0);
+  img.push_back(ImageF(width, height));
+  img.push_back(ImageF(width, height));
+  img.push_back(ImageF(width, height));
+  img.push_back(ImageF(width, height));
   for (int y = 0; y < height; y++) {
-    float* const img1_row_r = img1[0].Row(y);
-    float* const img1_row_g = img1[1].Row(y);
-    float* const img1_row_b = img1[2].Row(y);
-    float* const img1_row_a = img1[3].Row(y);
-    float* const img2_row_r = img2[0].Row(y);
-    float* const img2_row_g = img2[1].Row(y);
-    float* const img2_row_b = img2[2].Row(y);
-    float* const img2_row_a = img2[3].Row(y);
+    float* const row_r = img[0].Row(y);
+    float* const row_g = img[1].Row(y);
+    float* const row_b = img[2].Row(y);
+    float* const row_a = img[3].Row(y);
     for (int x = 0; x < width; x++) {
-      img1_row_r[x] = 255.0 * pow(rgba1p[y * width * 4 + x * 4 + 0] / 255.0, 2.2);
-      img1_row_g[x] = 255.0 * pow(rgba1p[y * width * 4 + x * 4 + 1] / 255.0, 2.2);
-      img1_row_b[x] = 255.0 * pow(rgba1p[y * width * 4 + x * 4 + 2] / 255.0, 2.2);
-      img1_row_a[x] = 255.0 * pow(rgba1p[y * width * 4 + x * 4 + 3] / 255.0, 2.2);
-      img2_row_r[x] = 255.0 * pow(rgba2p[y * width * 4 + x * 4 + 0] / 255.0, 2.2);
-      img2_row_g[x] = 255.0 * pow(rgba2p[y * width * 4 + x * 4 + 1] / 255.0, 2.2);
-      img2_row_b[x] = 255.0 * pow(rgba2p[y * width * 4 + x * 4 + 2] / 255.0, 2.2);
-      img2_row_a[x] = 255.0 * pow(rgba2p[y * width * 4 + x * 4 + 3] / 255.0, 2.2);
+      row_r[x] = 255.0 * pow(rgba[y * width * 4 + x * 4 + 0] / 255.0, gamma);
+      row_g[x] = 255.0 * pow(rgba[y * width * 4 + x * 4 + 1] / 255.0, gamma);
+      row_b[x] = 255.0 * pow(rgba[y * width * 4 + x * 4 + 2] / 255.0, gamma);
+      row_a[x] = 255.0 * pow(rgba[y * width * 4 + x * 4 + 3] / 255.0, gamma);
     }
   }
-
-  ImageF diffmap;
-  double diffvalue;
-  if (!ButteraugliInterface(img1, img2, 1.0, diffmap, diffvalue)) {
-    return -1.0;
-  }
-  return diffvalue;
 }
+class VisDiff {
+ private:
+  std::vector<ImageF> ref_img;
+  int width;
+  int height;
+
+ public:
+  VisDiff(std::string ref_img, int width, int height) {
+    planarize(this->ref_img, ref_img.c_str(), width, height);
+    this->width = width;
+    this->height = height;
+  }
+
+  double distance(std::string other_img) {
+    std::vector<ImageF> img;
+    planarize(img, other_img.c_str(), width, height);
+
+    ImageF diffmap;
+    double diffvalue;
+    if (!ButteraugliInterface(ref_img, img, 1.0, diffmap, diffvalue)) {
+      return -1.0;
+    }
+    return diffvalue;
+  }
+};
 
 EMSCRIPTEN_BINDINGS(my_module) {
-  function("visdif", &visdif);
+  class_<VisDiff>("VisDiff").constructor<std::string, int, int>().function("distance",
+                                                                           &VisDiff::distance);
 }
diff --git a/codecs/visdif/visdif.js b/codecs/visdif/visdif.js
index 420802cd..20a2d881 100644
--- a/codecs/visdif/visdif.js
+++ b/codecs/visdif/visdif.js
@@ -7,49 +7,64 @@ function(visdif) {
   visdif = visdif || {};
 
 
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   return visdif.ready
diff --git a/codecs/visdif/visdif.wasm b/codecs/visdif/visdif.wasm
index 19cf7489..782c122d 100644
Binary files a/codecs/visdif/visdif.wasm and b/codecs/visdif/visdif.wasm differ