Add downsampling option to SkJpegEncoder

Bug: 713862
Change-Id: Ibad6ecf836ccfd355499e1bace7bcd4ba772a97a
Reviewed-on: https://skia-review.googlesource.com/15891
Commit-Queue: Matt Sarett <msarett@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>

3 files changed, 119 insertions, 4 deletions

diff --git a/src/images/SkJpegEncoder.cpp b/src/images/SkJpegEncoder.cpp
index d87fed81bc..4b37cd3be3 100644
--- a/src/images/SkJpegEncoder.cpp
+++ b/src/images/SkJpegEncoder.cpp
@@ -152,6 +152,35 @@ bool SkJpegEncoderMgr::setParams(const SkImageInfo& srcInfo, const SkJpegEncoder
     fCInfo.input_components = numComponents;
     jpeg_set_defaults(&fCInfo);
 
+    if (kGray_8_SkColorType != srcInfo.colorType()) {
+        switch (options.fDownsample) {
+            case SkJpegEncoder::Downsample::k420:
+                SkASSERT(2 == fCInfo.comp_info[0].h_samp_factor);
+                SkASSERT(2 == fCInfo.comp_info[0].v_samp_factor);
+                SkASSERT(1 == fCInfo.comp_info[1].h_samp_factor);
+                SkASSERT(1 == fCInfo.comp_info[1].v_samp_factor);
+                SkASSERT(1 == fCInfo.comp_info[2].h_samp_factor);
+                SkASSERT(1 == fCInfo.comp_info[2].v_samp_factor);
+                break;
+            case SkJpegEncoder::Downsample::k422:
+                fCInfo.comp_info[0].h_samp_factor = 2;
+                fCInfo.comp_info[0].v_samp_factor = 1;
+                fCInfo.comp_info[1].h_samp_factor = 1;
+                fCInfo.comp_info[1].v_samp_factor = 1;
+                fCInfo.comp_info[2].h_samp_factor = 1;
+                fCInfo.comp_info[2].v_samp_factor = 1;
+                break;
+            case SkJpegEncoder::Downsample::k444:
+                fCInfo.comp_info[0].h_samp_factor = 1;
+                fCInfo.comp_info[0].v_samp_factor = 1;
+                fCInfo.comp_info[1].h_samp_factor = 1;
+                fCInfo.comp_info[1].v_samp_factor = 1;
+                fCInfo.comp_info[2].h_samp_factor = 1;
+                fCInfo.comp_info[2].v_samp_factor = 1;
+                break;
+        }
+    }
+
     // Tells libjpeg-turbo to compute optimal Huffman coding tables
     // for the image.  This improves compression at the cost of
     // slower encode performance.
diff --git a/src/images/SkJpegEncoder.h b/src/images/SkJpegEncoder.h
index 07290aeb9f..a8b9dfb540 100644
--- a/src/images/SkJpegEncoder.h
+++ b/src/images/SkJpegEncoder.h
@@ -21,6 +21,23 @@ public:
         kBlendOnBlack,
     };
 
+    enum class Downsample {
+        /**
+         *  Reduction by a factor of two in both the horizontal and vertical directions.
+         */
+        k420,
+
+        /**
+         *  Reduction by a factor of two in the horizontal direction.
+         */
+        k422,
+
+        /**
+         *  No downsampling.
+         */
+        k444,
+    };
+
     struct Options {
         /**
          *  |fQuality| must be in [0, 100] where 0 corresponds to the lowest quality.
@@ -28,6 +45,14 @@ public:
         int fQuality = 100;
 
         /**
+         *  Choose the downsampling factor for the U and V components.  This is only
+         *  meaningful if the |src| is not kGray, since kGray will not be encoded as YUV.
+         *
+         *  Our default value matches the libjpeg-turbo default.
+         */
+        Downsample fDownsample = Downsample::k420;
+
+        /**
          *  Jpegs must be opaque.  This instructs the encoder on how to handle input
          *  images with alpha.
          *
diff --git a/tests/EncodeTest.cpp b/tests/EncodeTest.cpp
index 45a0ff83aa..7046e671c9 100644
--- a/tests/EncodeTest.cpp
+++ b/tests/EncodeTest.cpp
@@ -86,7 +86,27 @@ DEF_TEST(Encode, r) {
     test_encode(r, SkEncodedImageFormat::kPNG);
 }
 
-static inline bool equals(const SkBitmap& a, const SkBitmap& b) {
+static inline bool almost_equals(SkPMColor a, SkPMColor b, int tolerance) {
+    if (SkTAbs((int)SkGetPackedR32(a) - (int)SkGetPackedR32(b)) > tolerance) {
+        return false;
+    }
+
+    if (SkTAbs((int)SkGetPackedG32(a) - (int)SkGetPackedG32(b)) > tolerance) {
+        return false;
+    }
+
+    if (SkTAbs((int)SkGetPackedB32(a) - (int)SkGetPackedB32(b)) > tolerance) {
+        return false;
+    }
+
+    if (SkTAbs((int)SkGetPackedA32(a) - (int)SkGetPackedA32(b)) > tolerance) {
+        return false;
+    }
+
+    return true;
+}
+
+static inline bool almost_equals(const SkBitmap& a, const SkBitmap& b, int tolerance) {
     if (a.info() != b.info()) {
         return false;
     }
@@ -94,7 +114,7 @@ static inline bool equals(const SkBitmap& a, const SkBitmap& b) {
     SkASSERT(kN32_SkColorType == a.colorType());
     for (int y = 0; y < a.height(); y++) {
         for (int x = 0; x < a.width(); x++) {
-            if (*a.getAddr32(x, y) != *b.getAddr32(x, y)) {
+            if (!almost_equals(*a.getAddr32(x, y), *b.getAddr32(x, y), tolerance)) {
                 return false;
             }
         }
@@ -103,6 +123,47 @@ static inline bool equals(const SkBitmap& a, const SkBitmap& b) {
     return true;
 }
 
+DEF_TEST(Encode_JpegDownsample, r) {
+    SkBitmap bitmap;
+    bool success = GetResourceAsBitmap("mandrill_128.png", &bitmap);
+    if (!success) {
+        return;
+    }
+
+    SkPixmap src;
+    success = bitmap.peekPixels(&src);
+    REPORTER_ASSERT(r, success);
+    if (!success) {
+        return;
+    }
+
+    SkDynamicMemoryWStream dst0, dst1, dst2;
+    SkJpegEncoder::Options options;
+    success = SkJpegEncoder::Encode(&dst0, src, options);
+    REPORTER_ASSERT(r, success);
+
+    options.fDownsample = SkJpegEncoder::Downsample::k422;
+    success = SkJpegEncoder::Encode(&dst1, src, options);
+    REPORTER_ASSERT(r, success);
+
+    options.fDownsample = SkJpegEncoder::Downsample::k444;
+    success = SkJpegEncoder::Encode(&dst2, src, options);
+    REPORTER_ASSERT(r, success);
+
+    sk_sp<SkData> data0 = dst0.detachAsData();
+    sk_sp<SkData> data1 = dst1.detachAsData();
+    sk_sp<SkData> data2 = dst2.detachAsData();
+    REPORTER_ASSERT(r, data0->size() < data1->size());
+    REPORTER_ASSERT(r, data1->size() < data2->size());
+
+    SkBitmap bm0, bm1, bm2;
+    SkImage::MakeFromEncoded(data0)->asLegacyBitmap(&bm0, SkImage::kRO_LegacyBitmapMode);
+    SkImage::MakeFromEncoded(data1)->asLegacyBitmap(&bm1, SkImage::kRO_LegacyBitmapMode);
+    SkImage::MakeFromEncoded(data2)->asLegacyBitmap(&bm2, SkImage::kRO_LegacyBitmapMode);
+    REPORTER_ASSERT(r, almost_equals(bm0, bm1, 60));
+    REPORTER_ASSERT(r, almost_equals(bm1, bm2, 60));
+}
+
 DEF_TEST(Encode_PngOptions, r) {
     SkBitmap bitmap;
     bool success = GetResourceAsBitmap("mandrill_128.png", &bitmap);
@@ -140,6 +201,6 @@ DEF_TEST(Encode_PngOptions, r) {
     SkImage::MakeFromEncoded(data0)->asLegacyBitmap(&bm0, SkImage::kRO_LegacyBitmapMode);
     SkImage::MakeFromEncoded(data1)->asLegacyBitmap(&bm1, SkImage::kRO_LegacyBitmapMode);
     SkImage::MakeFromEncoded(data2)->asLegacyBitmap(&bm2, SkImage::kRO_LegacyBitmapMode);
-    REPORTER_ASSERT(r, equals(bm0, bm1));
-    REPORTER_ASSERT(r, equals(bm0, bm2));
+    REPORTER_ASSERT(r, almost_equals(bm0, bm1, 0));
+    REPORTER_ASSERT(r, almost_equals(bm0, bm2, 0));
 }