diff --git a/aos/vision/blob/threshold.cc b/aos/vision/blob/threshold.cc
index 74809d1..36dcafe 100644
--- a/aos/vision/blob/threshold.cc
+++ b/aos/vision/blob/threshold.cc
@@ -4,20 +4,17 @@
 
 namespace aos {
 namespace vision {
+namespace {
 
-// Expands to a unique value for each combination of values for 5 bools.
-#define MASH(v0, v1, v2, v3, v4)                                  \
-  ((uint8_t(v0) << 4) | (uint8_t(v1) << 3) | (uint8_t(v2) << 2) | \
-   (uint8_t(v3) << 1) | (uint8_t(v4)))
+constexpr int kChunkSize = 8;
+
+}  // namespace
 
 // At a high level, the algorithm is the same as the slow thresholding, except
-// it operates in 4-pixel chunks. The handling for each of these chunks is
-// manually flattened (via codegen) into a 32-case switch statement. There are
-// 2^4 cases for each pixel being in or out, along with another set of cases
-// depending on whether the start of the chunk is in a range or not.
+// it operates in kChunkSize-pixel chunks.
 RangeImage FastYuyvYThreshold(ImageFormat fmt, const char *data,
                               uint8_t value) {
-  CHECK_EQ(0, fmt.w % 4);
+  CHECK_EQ(0, fmt.w % kChunkSize);
   std::vector<std::vector<ImageRange>> result;
   result.reserve(fmt.h);
 
@@ -28,195 +25,22 @@
     bool in_range = false;
     int current_range_start = -1;
     std::vector<ImageRange> current_row_ranges;
-    // Iterate through each 4-pixel chunk
-    for (int x = 0; x < fmt.w / 4; ++x) {
+    // Iterate through each kChunkSize-pixel chunk
+    for (int x = 0; x < fmt.w / kChunkSize; ++x) {
       // The per-channel (YUYV) values in the current chunk.
-      uint8_t chunk_channels[8];
-      memcpy(&chunk_channels[0], current_row + x * 4 * 2, 8);
-      const uint8_t pattern =
-          MASH(in_range, chunk_channels[0] > value, chunk_channels[2] > value,
-               chunk_channels[4] > value, chunk_channels[6] > value);
-      switch (pattern) {
-        // clang-format off
-/*
-# Ruby code to generate the below code:
-32.times do |v|
-        puts "case MASH(#{[v[4], v[3], v[2], v[1], v[0]].join(", ")}):"
-        in_range = v[4]
-        current_range_start = "current_range_start"
-        4.times do |i|
-                if v[3 - i] != in_range
-                        if (in_range == 1)
-                                puts "  current_row_ranges.emplace_back(ImageRange(#{current_range_start}, x * 4 + #{i}));"
-                        else
-                                current_range_start = "x * 4 + #{i}"
-                        end
-                        in_range = v[3 - i]
-                end
-        end
-        if (current_range_start != "current_range_start")
-                puts "  current_range_start = #{current_range_start};"
-        end
-        if (in_range != v[4])
-                puts "  in_range = #{["false", "true"][v[0]]};"
-        end
-        puts "  break;"
-end
-*/
-        // clang-format on
-        case MASH(0, 0, 0, 0, 0):
-          break;
-        case MASH(0, 0, 0, 0, 1):
-          current_range_start = x * 4 + 3;
-          in_range = true;
-          break;
-        case MASH(0, 0, 0, 1, 0):
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 2, x * 4 + 3));
-          current_range_start = x * 4 + 2;
-          break;
-        case MASH(0, 0, 0, 1, 1):
-          current_range_start = x * 4 + 2;
-          in_range = true;
-          break;
-        case MASH(0, 0, 1, 0, 0):
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 1, x * 4 + 2));
-          current_range_start = x * 4 + 1;
-          break;
-        case MASH(0, 0, 1, 0, 1):
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 1, x * 4 + 2));
-          current_range_start = x * 4 + 3;
-          in_range = true;
-          break;
-        case MASH(0, 0, 1, 1, 0):
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 1, x * 4 + 3));
-          current_range_start = x * 4 + 1;
-          break;
-        case MASH(0, 0, 1, 1, 1):
-          current_range_start = x * 4 + 1;
-          in_range = true;
-          break;
-        case MASH(0, 1, 0, 0, 0):
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 0, x * 4 + 1));
-          current_range_start = x * 4 + 0;
-          break;
-        case MASH(0, 1, 0, 0, 1):
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 0, x * 4 + 1));
-          current_range_start = x * 4 + 3;
-          in_range = true;
-          break;
-        case MASH(0, 1, 0, 1, 0):
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 0, x * 4 + 1));
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 2, x * 4 + 3));
-          current_range_start = x * 4 + 2;
-          break;
-        case MASH(0, 1, 0, 1, 1):
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 0, x * 4 + 1));
-          current_range_start = x * 4 + 2;
-          in_range = true;
-          break;
-        case MASH(0, 1, 1, 0, 0):
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 0, x * 4 + 2));
-          current_range_start = x * 4 + 0;
-          break;
-        case MASH(0, 1, 1, 0, 1):
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 0, x * 4 + 2));
-          current_range_start = x * 4 + 3;
-          in_range = true;
-          break;
-        case MASH(0, 1, 1, 1, 0):
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 0, x * 4 + 3));
-          current_range_start = x * 4 + 0;
-          break;
-        case MASH(0, 1, 1, 1, 1):
-          current_range_start = x * 4 + 0;
-          in_range = true;
-          break;
-        case MASH(1, 0, 0, 0, 0):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 0));
-          in_range = false;
-          break;
-        case MASH(1, 0, 0, 0, 1):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 0));
-          current_range_start = x * 4 + 3;
-          break;
-        case MASH(1, 0, 0, 1, 0):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 0));
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 2, x * 4 + 3));
-          current_range_start = x * 4 + 2;
-          in_range = false;
-          break;
-        case MASH(1, 0, 0, 1, 1):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 0));
-          current_range_start = x * 4 + 2;
-          break;
-        case MASH(1, 0, 1, 0, 0):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 0));
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 1, x * 4 + 2));
-          current_range_start = x * 4 + 1;
-          in_range = false;
-          break;
-        case MASH(1, 0, 1, 0, 1):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 0));
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 1, x * 4 + 2));
-          current_range_start = x * 4 + 3;
-          break;
-        case MASH(1, 0, 1, 1, 0):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 0));
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 1, x * 4 + 3));
-          current_range_start = x * 4 + 1;
-          in_range = false;
-          break;
-        case MASH(1, 0, 1, 1, 1):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 0));
-          current_range_start = x * 4 + 1;
-          break;
-        case MASH(1, 1, 0, 0, 0):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 1));
-          in_range = false;
-          break;
-        case MASH(1, 1, 0, 0, 1):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 1));
-          current_range_start = x * 4 + 3;
-          break;
-        case MASH(1, 1, 0, 1, 0):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 1));
-          current_row_ranges.emplace_back(ImageRange(x * 4 + 2, x * 4 + 3));
-          current_range_start = x * 4 + 2;
-          in_range = false;
-          break;
-        case MASH(1, 1, 0, 1, 1):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 1));
-          current_range_start = x * 4 + 2;
-          break;
-        case MASH(1, 1, 1, 0, 0):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 2));
-          in_range = false;
-          break;
-        case MASH(1, 1, 1, 0, 1):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 2));
-          current_range_start = x * 4 + 3;
-          break;
-        case MASH(1, 1, 1, 1, 0):
-          current_row_ranges.emplace_back(
-              ImageRange(current_range_start, x * 4 + 3));
-          in_range = false;
-          break;
-        case MASH(1, 1, 1, 1, 1):
-          break;
+      uint8_t chunk_channels[2 * kChunkSize];
+      memcpy(&chunk_channels[0], current_row + x * kChunkSize * 2, 2 * kChunkSize);
+
+      for (int i = 0; i < kChunkSize; ++i) {
+        if ((chunk_channels[i * 2] > value) != in_range) {
+          const int here = x * kChunkSize + i;
+          if (in_range) {
+            current_row_ranges.emplace_back(ImageRange(current_range_start, here));
+          } else {
+            current_range_start = here;
+          }
+          in_range = !in_range;
+        }
       }
     }
     if (in_range) {
@@ -227,7 +51,5 @@
   return RangeImage(0, std::move(result));
 }
 
-#undef MASH
-
 }  // namespace vision
 }  // namespace aos