[libcamera-devel] [PATCH v2 2/3] android: jpeg: Introduce a simple image thumbnailer

[Umang Jain]

Add a basic image Thumbnailer class for the frames being captured.
Currently, the thumbnailer can scale NV12 frames. It shall be used
to generate a thumbnail image for EXIF metadata, in the subsequent
commit.

Signed-off-by: Umang Jain <email at uajain.com>
---
 src/android/jpeg/thumbnailer.cpp | 113 +++++++++++++++++++++++++++++++
 src/android/jpeg/thumbnailer.h   |  36 ++++++++++
 src/android/meson.build          |   1 +
 3 files changed, 150 insertions(+)
 create mode 100644 src/android/jpeg/thumbnailer.cpp
 create mode 100644 src/android/jpeg/thumbnailer.h

diff --git a/src/android/jpeg/thumbnailer.cpp b/src/android/jpeg/thumbnailer.cpp
new file mode 100644
index 0000000..2e3c478
--- /dev/null
+++ b/src/android/jpeg/thumbnailer.cpp
@@ -0,0 +1,113 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2020, Google Inc.
+ *
+ * thumbnailer.cpp - Simple image thumbnailer
+ */
+
+#include "thumbnailer.h"
+
+#include <libcamera/formats.h>
+
+#include "libcamera/internal/log.h"
+
+using namespace libcamera;
+
+LOG_DEFINE_CATEGORY(Thumbnailer)
+
+Thumbnailer::Thumbnailer()
+	: valid_(false)
+{
+}
+
+void Thumbnailer::configure(const Size &sourceSize, PixelFormat pixelFormat)
+{
+	sourceSize_ = sourceSize;
+	pixelFormat_ = pixelFormat;
+
+	if (pixelFormat_ != formats::NV12) {
+		LOG (Thumbnailer, Error)
+			<< "Failed to configure: Pixel Format "
+			<< pixelFormat_.toString() << " unsupported.";
+		return;
+	}
+
+	targetSize_ = computeThumbnailSize();
+
+	valid_ = true;
+}
+
+/*
+ * The Exif specification recommends the width of the thumbnail to be a
+ * multiple of 16 (section 4.8.1). Hence, compute the corresponding height
+ * keeping the aspect ratio same as of the source.
+ */
+Size Thumbnailer::computeThumbnailSize() const
+{
+	unsigned int targetHeight;
+	constexpr unsigned int kTargetWidth = 160;
+
+	targetHeight = kTargetWidth * sourceSize_.height / sourceSize_.width;
+
+	if (targetHeight & 1)
+		targetHeight++;
+
+	return Size(kTargetWidth, targetHeight);
+}
+
+void
+Thumbnailer::createThumbnail(const FrameBuffer &source,
+			     std::vector<unsigned char> *destination)
+{
+	MappedFrameBuffer frame(&source, PROT_READ);
+	if (!frame.isValid()) {
+		LOG(Thumbnailer, Error)
+			<< "Failed to map FrameBuffer : "
+			<< strerror(frame.error());
+		return;
+	}
+
+	if (!valid_) {
+		LOG(Thumbnailer, Error) << "Config is unconfigured or invalid.";
+		return;
+	}
+
+	const unsigned int sw = sourceSize_.width;
+	const unsigned int sh = sourceSize_.height;
+	const unsigned int tw = targetSize_.width;
+	const unsigned int th = targetSize_.height;
+
+	ASSERT(tw % 2 == 0 && th % 2 == 0);
+
+	/* Image scaling block implementing nearest-neighbour algorithm. */
+	unsigned char *src = static_cast<unsigned char *>(frame.maps()[0].data());
+	unsigned char *srcC = src + sh * sw;
+	unsigned char *srcCb, *srcCr;
+	unsigned char *dstY, *srcY;
+
+	size_t dstSize = (th * tw) + ((th / 2) * tw);
+	destination->resize(dstSize);
+	unsigned char *dst = destination->data();
+	unsigned char *dstC = dst + th * tw;
+
+	for (unsigned int y = 0; y < th; y += 2) {
+		unsigned int sourceY = (sh * y + th / 2) / th;
+
+		dstY = dst + y * tw;
+		srcY = src + sw * sourceY;
+		srcCb = srcC + (sourceY / 2) * sw + 0;
+		srcCr = srcC + (sourceY / 2) * sw + 1;
+
+		for (unsigned int x = 0; x < tw; x += 2) {
+			unsigned int sourceX = (sw * x + tw / 2) / tw;
+
+			dstY[x] = srcY[sourceX];
+			dstY[tw + x] = srcY[sw + sourceX];
+			dstY[x + 1] = srcY[sourceX + 1];
+			dstY[tw + x + 1] = srcY[sw + sourceX + 1];
+
+			dstC[(y / 2) * tw + x + 0] = srcCb[(sourceX / 2) * 2];
+			dstC[(y / 2) * tw + x + 1] = srcCr[(sourceX / 2) * 2];
+		}
+	}
+}
diff --git a/src/android/jpeg/thumbnailer.h b/src/android/jpeg/thumbnailer.h
new file mode 100644
index 0000000..16e6951
--- /dev/null
+++ b/src/android/jpeg/thumbnailer.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2020, Google Inc.
+ *
+ * thumbnailer.h - Simple image thumbnailer
+ */
+#ifndef __ANDROID_JPEG_THUMBNAILER_H__
+#define __ANDROID_JPEG_THUMBNAILER_H__
+
+#include <libcamera/geometry.h>
+
+#include "libcamera/internal/buffer.h"
+#include "libcamera/internal/formats.h"
+
+class Thumbnailer
+{
+public:
+	Thumbnailer();
+
+	void configure(const libcamera::Size &sourceSize,
+		       libcamera::PixelFormat pixelFormat);
+	void createThumbnail(const libcamera::FrameBuffer &source,
+			     std::vector<unsigned char> *dest);
+	const libcamera::Size& size() const { return targetSize_; }
+
+private:
+	libcamera::Size computeThumbnailSize() const;
+
+	libcamera::PixelFormat pixelFormat_;
+	libcamera::Size sourceSize_;
+	libcamera::Size targetSize_;
+
+	bool valid_;
+};
+
+#endif /* __ANDROID_JPEG_THUMBNAILER_H__ */
diff --git a/src/android/meson.build b/src/android/meson.build
index f72376a..3d4d3be 100644
--- a/src/android/meson.build
+++ b/src/android/meson.build
@@ -25,6 +25,7 @@ android_hal_sources = files([
     'jpeg/encoder_libjpeg.cpp',
     'jpeg/exif.cpp',
     'jpeg/post_processor_jpeg.cpp',
+    'jpeg/thumbnailer.cpp',
 ])
 
 android_camera_metadata_sources = files([
-- 
2.26.2