From 8f9c9d0f88374573f32d76cf7d3a8fde9ca83f87 Mon Sep 17 00:00:00 2001
From: samrobinson <samrobinson@google.com>
Date: Fri, 9 Sep 2022 15:33:08 +0000
Subject: [PATCH] Rollback of
 https://github.com/google/ExoPlayer/commit/eb6c1183b69d319a610d79ef57028f62e74a7614

*** Original commit ***

Handle int instead of byte in SSIM.

The value of pixels are converted to integers at the point of use,
move this logic to the initialisation step.

This is a prerequisite step for testing SSIM calculation, which
will lead on to some SSIM improvements being verifiable.

Tested manually and SSIM values match for the same video
before and after this change.

***

PiperOrigin-RevId: 473259446
---
 .../exoplayer2/transformer/SsimHelper.java    | 27 +++++++++----------
 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/library/transformer/src/androidTest/java/com/google/android/exoplayer2/transformer/SsimHelper.java b/library/transformer/src/androidTest/java/com/google/android/exoplayer2/transformer/SsimHelper.java
index e4e51b8f7d5..0eb3bce3ef1 100644
--- a/library/transformer/src/androidTest/java/com/google/android/exoplayer2/transformer/SsimHelper.java
+++ b/library/transformer/src/androidTest/java/com/google/android/exoplayer2/transformer/SsimHelper.java
@@ -80,8 +80,8 @@ public static double calculate(
         new VideoDecodingWrapper(context, referenceVideoPath, DEFAULT_COMPARISON_INTERVAL);
     VideoDecodingWrapper distortedDecodingWrapper =
         new VideoDecodingWrapper(context, distortedVideoPath, DEFAULT_COMPARISON_INTERVAL);
-    @Nullable int[] referenceLumaBuffer = null;
-    @Nullable int[] distortedLumaBuffer = null;
+    @Nullable byte[] referenceLumaBuffer = null;
+    @Nullable byte[] distortedLumaBuffer = null;
     double accumulatedSsim = 0.0;
     int comparedImagesCount = 0;
     try {
@@ -101,10 +101,10 @@ public static double calculate(
         assertThat(distortedImage.getHeight()).isEqualTo(height);
 
         if (referenceLumaBuffer == null || referenceLumaBuffer.length != width * height) {
-          referenceLumaBuffer = new int[width * height];
+          referenceLumaBuffer = new byte[width * height];
         }
         if (distortedLumaBuffer == null || distortedLumaBuffer.length != width * height) {
-          distortedLumaBuffer = new int[width * height];
+          distortedLumaBuffer = new byte[width * height];
         }
         try {
           accumulatedSsim +=
@@ -134,7 +134,7 @@ public static double calculate(
    * @param lumaChannelBuffer The buffer where the extracted luma values are stored.
    * @return The {@code lumaChannelBuffer} for convenience.
    */
-  private static int[] extractLumaChannelBuffer(Image image, int[] lumaChannelBuffer) {
+  private static byte[] extractLumaChannelBuffer(Image image, byte[] lumaChannelBuffer) {
     // This method is invoked on the main thread.
     // `image` should contain YUV channels.
     Image.Plane[] imagePlanes = image.getPlanes();
@@ -147,8 +147,7 @@ private static int[] extractLumaChannelBuffer(Image image, int[] lumaChannelBuff
     ByteBuffer lumaByteBuffer = lumaPlane.getBuffer();
     for (int y = 0; y < height; y++) {
       for (int x = 0; x < width; x++) {
-        lumaChannelBuffer[y * width + x] =
-            lumaByteBuffer.get(y * rowStride + x * pixelStride) & 0xFF;
+        lumaChannelBuffer[y * width + x] = lumaByteBuffer.get(y * rowStride + x * pixelStride);
       }
     }
     return lumaChannelBuffer;
@@ -364,7 +363,7 @@ private static final class MssimCalculator {
      * @return The MSSIM score between the input images.
      */
     public static double calculate(
-        int[] referenceBuffer, int[] distortedBuffer, int width, int height) {
+        byte[] referenceBuffer, byte[] distortedBuffer, int width, int height) {
       double totalSsim = 0;
       int windowsCount = 0;
 
@@ -451,11 +450,11 @@ private static double getWindowSsim(
 
     /** Returns the mean of the pixels in the window. */
     private static double getMean(
-        int[] pixelBuffer, int bufferIndexOffset, int stride, int windowWidth, int windowHeight) {
+        byte[] pixelBuffer, int bufferIndexOffset, int stride, int windowWidth, int windowHeight) {
       double total = 0;
       for (int y = 0; y < windowHeight; y++) {
         for (int x = 0; x < windowWidth; x++) {
-          total += pixelBuffer[get1dIndex(x, y, stride, bufferIndexOffset)];
+          total += pixelBuffer[get1dIndex(x, y, stride, bufferIndexOffset)] & 0xFF;
         }
       }
       return total / (windowWidth * windowHeight);
@@ -463,8 +462,8 @@ private static double getMean(
 
     /** Calculates the variances and covariance of the pixels in the window for both buffers. */
     private static double[] getVariancesAndCovariance(
-        int[] referenceBuffer,
-        int[] distortedBuffer,
+        byte[] referenceBuffer,
+        byte[] distortedBuffer,
         double referenceMean,
         double distortedMean,
         int bufferIndexOffset,
@@ -477,8 +476,8 @@ private static double[] getVariancesAndCovariance(
       for (int y = 0; y < windowHeight; y++) {
         for (int x = 0; x < windowWidth; x++) {
           int index = get1dIndex(x, y, stride, bufferIndexOffset);
-          double referencePixelDeviation = referenceBuffer[index] - referenceMean;
-          double distortedPixelDeviation = distortedBuffer[index] - distortedMean;
+          double referencePixelDeviation = (referenceBuffer[index] & 0xFF) - referenceMean;
+          double distortedPixelDeviation = (distortedBuffer[index] & 0xFF) - distortedMean;
           referenceVariance += referencePixelDeviation * referencePixelDeviation;
           distortedVariance += distortedPixelDeviation * distortedPixelDeviation;
           referenceDistortedCovariance += referencePixelDeviation * distortedPixelDeviation;