diff --git a/src/main/java/band/full/testing/video/core/Plane.java b/src/main/java/band/full/testing/video/core/Plane.java
index b74819d..bdf12ab 100644
--- a/src/main/java/band/full/testing/video/core/Plane.java
+++ b/src/main/java/band/full/testing/video/core/Plane.java
@@ -1,9 +1,11 @@
 package band.full.testing.video.core;
 
 import static java.lang.Math.abs;
+import static java.util.stream.IntStream.range;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 
 import java.util.Arrays;
+import java.util.stream.IntStream;
 
 /**
  * @author Igor Malinin
@@ -70,14 +72,17 @@ public void verifyRect(int x, int y, int w, int h, int expected,
         int x2 = limit(x + w, width);
         int y2 = limit(y + h, height);
 
-        int count = 0, total = (y2 - y1) * (x2 - x1);
+        IntStream range = range(y1, y2);
+        if (x2 - x1 > 64) { // TODO measure when to switch
+            range = range.parallel();
+        }
 
-        for (int iy = y1; iy < y2; iy++) {
+        int count = range.map(iy -> {
             int base = iy * width;
-            count += verify(base + x1, base + x2, expected, deviation);
-        }
+            return verify(base + x1, base + x2, expected, deviation);
+        }).sum();
 
-        assertFalse(count + maxMisses < total);
+        assertFalse(count + maxMisses < (y2 - y1) * (x2 - x1));
     }
 
     private int verify(int from, int to, int expected, int deviation) {
diff --git a/src/test/java/band/full/testing/video/generate/QuantizationBase.java b/src/test/java/band/full/testing/video/generate/QuantizationBase.java
index c0f3665..3c98bb2 100644
--- a/src/test/java/band/full/testing/video/generate/QuantizationBase.java
+++ b/src/test/java/band/full/testing/video/generate/QuantizationBase.java
@@ -88,7 +88,7 @@ protected void verify(DecoderY4M d, int yMin, boolean redChroma) {
 
     protected void verify(CanvasYCbCr canvas, int yMin, boolean redChroma) {
         range(0, ROWS).forEach(row -> {
-            range(0, COLS).forEach(col -> {
+            range(0, COLS).parallel().forEach(col -> {
                 int yCode = yMin + col;
                 int cCode = canvas.parameters.ACHROMATIC - ROWS / 2 + row;