YUV420转RGBA之使用opencv

前面在《YUV_420_888介绍及YUV420转RGBA》一文中介绍了YUV420的转换，并提供了自己写的转换代码。但是实际项目中一般不会自己手写代码逐个像素去转换，因为这样转换的速度比较慢。通常我们可以使用opencv或者libyuv来进行转换。本文就介绍使用opencv进行转换。

YUV420转RGBA系列共三篇：

YUV_420_888介绍及YUV420转RGBA
YUV420转RGBA之使用opencv
YUV420转RGBA之使用libyuv

本文是其中的第二篇。

1. 下载opencv

https://github.com/opencv/opencv/releases
可以下载opencv源码自行编译，也可以选择编译好的opencv-xxx-android-sdk。这里只是简单说明opencv的用法，就直接使用了opencv-3.4.10-android-sdk。

2. 导入opencv到Android Studio

导入opencv有两种方式：

直接使用opencv提供的Java版本 API
导入头文件和库文件，自己编写JNI调用opencv C/C++版本 API
这里选择第二种，自己编写JNI调用opencv C/C++版本 API。

2.1 导入头文件

在项目的app/src/main/cpp/下新建include文件夹。解压opencv-3.4.10-android-sdk压缩包，将～/opencv-3.4.10-android-sdk/OpenCV-android-sdk/sdk/native/jni/include/下面的头文件拷贝到项目的app/src/main/cpp/include下：

1.png

2.png

2.2 导入库文件

将~/sw/opencv-3.4.10-android-sdk/OpenCV-android-sdk/sdk/native/libs下的库文件拷贝项目的app/src/main/jniLibs下：

4.png

3.png

2.3 修改CMakeLists.txt

include_directories(${CMAKE_SOURCE_DIR}/include)
find_library(log-lib log)

add_library(opencv3 SHARED IMPORTED)
set_target_properties(
        opencv3
        PROPERTIES
        IMPORTED_LOCATION ${CMAKE_SOURCE_DIR}/../jniLibs/${ANDROID_ABI}/libopencv_java3.so
)

add_library(
        OpencvUtils
        SHARED
        opencv.cpp
        opencv_utils.cpp
)
target_link_libraries(OpencvUtils opencv3 ${log-lib})

修改完成后同步一下项目，接下来我们只要在opencv.cpp和 opencv_utils.cpp中编码调用opencv 的API就可以了。

3. 使用opencv将YUV420转换成RGBA

opencv.cpp：

#include 
#include 
#include "opencv_utils.h"

extern "C"
JNIEXPORT void JNICALL
Java_com_qxt_yuv420_OpencvUtils_I420ToRGBA(JNIEnv *env, jclass clazz,
                                           jbyteArray src, jbyteArray dst,
                                           jint width, jint height) {
    jbyte *_src = env->GetByteArrayElements(src, nullptr);
    jbyte *_dst = env->GetByteArrayElements(dst, nullptr);
    opencvI420ToRGBA(reinterpret_cast(_src),
                     reinterpret_cast(_dst), width, height);
    env->ReleaseByteArrayElements(src, _src, JNI_ABORT);
    env->ReleaseByteArrayElements(dst, _dst, 0);
}

extern "C"
JNIEXPORT void JNICALL
Java_com_qxt_yuv420_OpencvUtils_YV12ToRGBA(JNIEnv *env, jclass clazz,
                                           jbyteArray src, jbyteArray dst,
                                           jint width, jint height) {
    jbyte *_src = env->GetByteArrayElements(src, nullptr);
    jbyte *_dst = env->GetByteArrayElements(dst, nullptr);
    opencvYV12ToRGBA(reinterpret_cast(_src),
                     reinterpret_cast(_dst), width, height);
    env->ReleaseByteArrayElements(src, _src, JNI_ABORT);
    env->ReleaseByteArrayElements(dst, _dst, 0);
}

extern "C"
JNIEXPORT void JNICALL
Java_com_qxt_yuv420_OpencvUtils_NV12ToRGBA(JNIEnv *env, jclass clazz,
                                           jbyteArray src, jbyteArray dst,
                                           jint width, jint height) {
    jbyte *_src = env->GetByteArrayElements(src, nullptr);
    jbyte *_dst = env->GetByteArrayElements(dst, nullptr);
    opencvNV12ToRGBA(reinterpret_cast(_src),
                     reinterpret_cast(_dst), width, height);
    env->ReleaseByteArrayElements(src, _src, JNI_ABORT);
    env->ReleaseByteArrayElements(dst, _dst, 0);
}

extern "C"
JNIEXPORT void JNICALL
Java_com_qxt_yuv420_OpencvUtils_NV21ToRGBA(JNIEnv *env, jclass clazz,
                                           jbyteArray src, jbyteArray dst,
                                           jint width, jint height) {
    jbyte *_src = env->GetByteArrayElements(src, nullptr);
    jbyte *_dst = env->GetByteArrayElements(dst, nullptr);
    opencvNV21ToRGBA(reinterpret_cast(_src),
                     reinterpret_cast(_dst), width, height);
    env->ReleaseByteArrayElements(src, _src, JNI_ABORT);
    env->ReleaseByteArrayElements(dst, _dst, 0);
}

opencv_utils.h:

#ifndef OPENCV_UTILS_H
#define OPENCV_UTILS_H

#ifdef __cplusplus
extern "C" {
#endif

void opencvI420ToRGBA(unsigned char *src, unsigned char *dst, int width, int height);

void opencvYV12ToRGBA(unsigned char *src, unsigned char *dst, int width, int height);

void opencvNV12ToRGBA(unsigned char *src, unsigned char *dst, int width, int height);

void opencvNV21ToRGBA(unsigned char *src, unsigned char *dst, int width, int height);

#ifdef __cplusplus
}
#endif
#endif //OPENCV_UTILS_H

opencv_utils.cpp:

#include 
#include 
#include 

#include "logger.h"
#include "opencv_utils.h"

using namespace std;
using namespace cv;

void opencvI420ToRGBA(unsigned char *src, unsigned char *dst, int width, int height) {
    Mat srcImg(height * 3 / 2, width, CV_8UC1, src);
    Mat dstImg(height, width, CV_8UC4, dst);
    cvtColor(srcImg, dstImg, CV_YUV2RGBA_I420);
}

void opencvYV12ToRGBA(unsigned char *src, unsigned char *dst, int width, int height) {
    Mat srcImg(height * 3 / 2, width, CV_8UC1, src);
    Mat dstImg(height, width, CV_8UC4, dst);
    cvtColor(srcImg, dstImg, CV_YUV2RGBA_YV12);
}

void opencvNV12ToRGBA(unsigned char *src, unsigned char *dst, int width, int height) {
    Mat srcImg(height * 3 / 2, width, CV_8UC1, src);
    Mat dstImg(height, width, CV_8UC4, dst);
    cvtColor(srcImg, dstImg, CV_YUV2RGBA_NV12);
}

void opencvNV21ToRGBA(unsigned char *src, unsigned char *dst, int width, int height) {
    Mat srcImg(height * 3 / 2, width, CV_8UC1, src);
    Mat dstImg(height, width, CV_8UC4, dst);
    cvtColor(srcImg, dstImg, CV_YUV2RGBA_NV21);
}

4. 使用opencv旋转RGBA和YUV420P