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：

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 <jni.h>
#include <string>
#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<unsigned char *>(_src),
                     reinterpret_cast<unsigned char *>(_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<unsigned char *>(_src),
                     reinterpret_cast<unsigned char *>(_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<unsigned char *>(_src),
                     reinterpret_cast<unsigned char *>(_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<unsigned char *>(_src),
                     reinterpret_cast<unsigned char *>(_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 <stdint.h>
#include <opencv2/opencv.hpp>
#include <opencv2/core/core.hpp>
#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
opencv.cpp：
extern "C"
JNIEXPORT void JNICALL
Java_com_qxt_yuv420_OpencvUtils_rotateRGB(JNIEnv *env, jclass clazz, jbyteArray src,
                                          jint width, jint height, jfloat degree) {
    jbyte *_src = env->GetByteArrayElements(src, nullptr);
    opencvRotateRGB(reinterpret_cast<unsigned char *>(_src), width, height, degree);
    env->ReleaseByteArrayElements(src, _src, 0);
extern "C"
JNIEXPORT void JNICALL
Java_com_qxt_yuv420_OpencvUtils_rotateRGBA(JNIEnv *env, jclass clazz, jbyteArray src,
                                           jint width, jint height, jfloat degree) {
    jbyte *_src = env->GetByteArrayElements(src, nullptr);
    opencvRotateRGBA(reinterpret_cast<unsigned char *>(_src), width, height, degree);
    env->ReleaseByteArrayElements(src, _src, 0);
extern "C"
JNIEXPORT void JNICALL
Java_com_qxt_yuv420_OpencvUtils_rotateYUV420P(JNIEnv *env, jclass clazz, jbyteArray src,
                                              jint width, jint height, jfloat degree) {
    jbyte *_src = env->GetByteArrayElements(src, nullptr);
    opencvRotateYUV420P(reinterpret_cast<unsigned char *>(_src), width, height, degree);
    env->ReleaseByteArrayElements(src, _src, 0);
opencv_utils.h:
void opencvRotateRGB(unsigned char *src, int width, int height, float degree);
void opencvRotateRGBA(unsigned char *src, int width, int height, float degree);
void opencvRotateYUV420P(unsigned char *src, int width, int height, float degree);
opencv_utils.cpp:
static inline void rotate(Mat srcImg, float degree, int stride) {
    Mat tmpImg;
    Mat finalImg;
    if (degree == 90.0f /*ROTATE_90_CLOCKWISE*/) {
        transpose(srcImg, tmpImg);
        flip(tmpImg, finalImg, 1);
    } else if (degree == 180.0f /*ROTATE_180*/) {
        flip(srcImg, finalImg, -1);
    } else if (degree == 270.0f /*ROTATE_90_COUNTERCLOCKWISE*/) {
        transpose(srcImg, tmpImg);
        flip(tmpImg, finalImg, 0);
    } else {
        return;
    memcpy(srcImg.data, finalImg.data,
           static_cast<size_t>(finalImg.rows * finalImg.cols * stride));
    if (!tmpImg.empty()) {
        tmpImg.release();
    if (!finalImg.empty()) {
        finalImg.release();
void opencvRotateRGB(unsigned char *src, int width, int height, float degree) {
    Mat srcImg(height, width, CV_8UC3, src);
    rotate(srcImg, degree, 3);
void opencvRotateRGBA(unsigned char *src, int width, int height, float degree) {
    Mat srcImg(height, width, CV_8UC4, src);
    rotate(srcImg, degree, 4);
void opencvRotateYUV420P(unsigned char *src, int width, int height, float degree) {
    int uvWidth = width >> 1;
    int uvHeight = height >> 1;
    unsigned char *pY = src;
    unsigned char *pU = src + width * height;
    unsigned char *pV = src + width * height * 5 / 4;
    Mat y(height, width, CV_8UC1, pY);
    rotate(y, degree, 1);
    Mat u(uvHeight, uvWidth, CV_8UC1, pU);
    rotate(u, degree, 1);