概述
在封装so库的时候，底层c++代码的实现使用了OpenCV对图片进行操作，而Android中从摄像头中获取到的图片数据类型是Bitmap数据类型的，所以这里就避免不了做数据类型的转换。转换的方案主要有两种，
-
一种是封装的JNI接口方法直接接收cv::Mat数据类型的参数，
-
第二种是JNI方法的接口接收Bitmap数据类型的参数，在JNI中实现Bitmap到cv::Mat的转换。
– 资料
JNI将Android Bitmap转为OpenCV的Mat_jni bitmap 转为mat_修炼之路的博客-CSDN博客
使用OpenCV的SDK实现数据类型的转换
第一种方法，如果想在Android中使用cv::Mat的数据类型，我们可以直接通过导入OpenCV的SDK，然后通过opencv的Utils实现bitmap到cv::Mat的转换。
缺点在于需要添加opencv的库文件，会导致最终的apk文件变大。
Android studio中添加OpenCV SDK参考：Android 使用OpenCV SDK 开源库—傻瓜式教程_opencvsdk用法_sunbofiy23的博客-CSDN博客
方式一：
import org.opencv.android.Utils;
Mat mat = new Mat();
Bitmap bmp32 = bmp.copy(Bitmap.Config.ARGB_8888, true);
Utils.bitmapToMat(bmp32, mat);
在JNI中接收Mat参数的时候，使用Jobject类型，然后再做个强制转换就行了
方式二：
Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.my_image);
Mat mat = new Mat(bitmap.getHeight(), bitmap.getWidth(), CvType.CV_8UC4);
Utils.bitmapToMat(bitmap, mat);
其中，CvType.CV_8UC4 表示位图的数据类型为 8 位无符号整数，该类型表示每个像素使用 4 个通道（RGBA）。
方式三：
Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.my_image);
Mat mat = new Mat();
mat.create(bitmap.getHeight(), bitmap.getWidth(), CvType.CV_8UC4);
Utils.bitmapToMat(bitmap, mat);
其中，mat.create 方法用于创建一个空的 cv::Mat 对象，并指定其行数、列数和数据类型。
需要注意的是，Utils.bitmapToMat 是 OpenCV 中的辅助方法，用于将 Android 的 Bitmap 转换为 cv::Mat，需要在使用前确保已经导入 OpenCV 库。
JNI实现Bitmap到Mat的转换
– 代码1–CSDN找的
JNI将Android Bitmap转为OpenCV的Mat_jni bitmap 转为mat_修炼之路的博客-CSDN博客
#include <android/bitmap.h>
#include <opencv/cv.hpp>
#include <opencv2/opencv.hpp>
#include <opencv2/core.hpp>
#define ASSERT(status, ret) if (!(status)) { return ret; }
#define ASSERT_FALSE(status) ASSERT(status, false)
bool BitmapToMatrix(JNIEnv * env, jobject obj_bitmap, cv::Mat & matrix) {
void * bitmapPixels; // Save picture pixel data
AndroidBitmapInfo bitmapInfo; // Save picture parameters
ASSERT_FALSE( AndroidBitmap_getInfo(env, obj_bitmap, &bitmapInfo) >= 0); // Get picture parameters
ASSERT_FALSE( bitmapInfo.format == ANDROID_BITMAP_FORMAT_RGBA_8888
|| bitmapInfo.format == ANDROID_BITMAP_FORMAT_RGB_565 ); // Only ARGB? 8888 and RGB? 565 are supported
ASSERT_FALSE( AndroidBitmap_lockPixels(env, obj_bitmap, &bitmapPixels) >= 0 ); // Get picture pixels (lock memory block)
ASSERT_FALSE( bitmapPixels );
if (bitmapInfo.format == ANDROID_BITMAP_FORMAT_RGBA_8888) {
cv::Mat tmp(bitmapInfo.height, bitmapInfo.width, CV_8UC4, bitmapPixels); // Establish temporary mat
tmp.copyTo(matrix); // Copy to target matrix
} else {
cv::Mat tmp(bitmapInfo.height, bitmapInfo.width, CV_8UC2, bitmapPixels);
cv::cvtColor(tmp, matrix, cv::COLOR_BGR5652RGB);
}
//convert RGB to BGR
cv::cvtColor(matrix,matrix,cv::COLOR_RGB2BGR);
AndroidBitmap_unlockPixels(env, obj_bitmap); // Unlock
return true;
}
bool MatrixToBitmap(JNIEnv * env, cv::Mat & matrix, jobject obj_bitmap) {
void * bitmapPixels; // Save picture pixel data
AndroidBitmapInfo bitmapInfo; // Save picture parameters
ASSERT_FALSE( AndroidBitmap_getInfo(env, obj_bitmap, &bitmapInfo) >= 0); // Get picture parameters
ASSERT_FALSE( bitmapInfo.format == ANDROID_BITMAP_FORMAT_RGBA_8888
|| bitmapInfo.format == ANDROID_BITMAP_FORMAT_RGB_565 ); // Only ARGB? 8888 and RGB? 565 are supported
ASSERT_FALSE( matrix.dims == 2
&& bitmapInfo.height == (uint32_t)matrix.rows
&& bitmapInfo.width == (uint32_t)matrix.cols ); // It must be a 2-dimensional matrix with the same length and width
ASSERT_FALSE( matrix.type() == CV_8UC1 || matrix.type() == CV_8UC3 || matrix.type() == CV_8UC4 );
ASSERT_FALSE( AndroidBitmap_lockPixels(env, obj_bitmap, &bitmapPixels) >= 0 ); // Get picture pixels (lock memory block)
ASSERT_FALSE( bitmapPixels );
if (bitmapInfo.format == ANDROID_BITMAP_FORMAT_RGBA_8888) {
cv::Mat tmp(bitmapInfo.height, bitmapInfo.width, CV_8UC4, bitmapPixels);
switch (matrix.type()) {
case CV_8UC1: cv::cvtColor(matrix, tmp, cv::COLOR_GRAY2RGBA); break;
case CV_8UC3: cv::cvtColor(matrix, tmp, cv::COLOR_RGB2RGBA); break;
case CV_8UC4: matrix.copyTo(tmp); break;
default: AndroidBitmap_unlockPixels(env, obj_bitmap); return false;
}
} else {
cv::Mat tmp(bitmapInfo.height, bitmapInfo.width, CV_8UC2, bitmapPixels);
switch (matrix.type()) {
case CV_8UC1: cv::cvtColor(matrix, tmp, cv::COLOR_GRAY2BGR565); break;
case CV_8UC3: cv::cvtColor(matrix, tmp, cv::COLOR_RGB2BGR565); break;
case CV_8UC4: cv::cvtColor(matrix, tmp, cv::COLOR_RGBA2BGR565); break;
default: AndroidBitmap_unlockPixels(env, obj_bitmap); return false;
}
}
AndroidBitmap_unlockPixels(env, obj_bitmap); // Unlock
return true;
}
JNIEXPORT void JNICALL
Java_com_example_MainActivity_JniBitmapExec(JNIEnv * env, jobject /* this */,
jobject obj_bitmap, jobject obj_bitmapOut)
{
cv::Mat matBitmap;
bool ret = BitmapToMatrix(env, obj_bitmap, matBitmap); // Bitmap to cv::Mat
if (ret == false) {
return;
}
// opencv processing of mat
ret = MatrixToBitmap(env, matBitmap, obj_bitmapOut); // Bitmap to cv::Mat
if (ret == false) {
return;
}
}
注意在CMakelist文件中添加以下代码，不然编译的时候会报错:文章来源：https://www.toymoban.com/news/detail-790095.html
target_link_libraries( # Specifies the target library.
#在target_link_libraries中添加下面的依赖项
jnigraphics
)
– 代码2 – chatGpt中写的代码
#include <jni.h>
#include <opencv2/opencv.hpp>
using namespace cv;
extern "C"
JNIEXPORT void JNICALL
Java_com_example_android_MainActivity_nativeBitmapToMat(JNIEnv *env, jobject thiz,
jobject bitmap) {
AndroidBitmapInfo info;
void* pixels;
Mat img;
// 获取 Bitmap 的信息与像素数据
if (AndroidBitmap_getInfo(env, bitmap, &info) != ANDROID_BITMAP_RESULT_SUCCESS ||
AndroidBitmap_lockPixels(env, bitmap, &pixels) != ANDROID_BITMAP_RESULT_SUCCESS) {
return;
}
// 创建 Mat 对象并拷贝像素数据
img.create(info.height, info.width, CV_8UC4);
memcpy(img.data, pixels, info.stride * info.height);
// 解锁像素数据，释放资源
AndroidBitmap_unlockPixels(env, bitmap);
}
– 代码3 – paddle fastdeploy中 实现
https://github.com/PaddlePaddle/FastDeploy/blob/develop/java/android/fastdeploy/src/main/cpp/fastdeploy_jni/bitmap_jni.cc文章来源地址https://www.toymoban.com/news/detail-790095.html
#include <android/bitmap.h>
#include <opencv2/opencv.hpp>
cv::Mat CreateZeroCopyRGBAFromBitmap(JNIEnv *env, jobject j_argb8888_bitmap) {
cv::Mat c_rgba;
AndroidBitmapInfo j_bitmap_info;
if (AndroidBitmap_getInfo(env, j_argb8888_bitmap, &j_bitmap_info) < 0) {
LOGE("Invoke AndroidBitmap_getInfo() failed!");
return c_rgba;
}
if (j_bitmap_info.format != ANDROID_BITMAP_FORMAT_RGBA_8888) {
LOGE("Only Bitmap.Config.ARGB8888 color format is supported!");
return c_rgba;
}
void *j_bitmap_pixels;
if (AndroidBitmap_lockPixels(env, j_argb8888_bitmap, &j_bitmap_pixels) < 0) {
LOGE("Invoke AndroidBitmap_lockPixels() failed!");
return c_rgba;
}
cv::Mat j_bitmap_im(static_cast<int>(j_bitmap_info.height),
static_cast<int>(j_bitmap_info.width), CV_8UC4,
j_bitmap_pixels); // no copied.
c_rgba = j_bitmap_im; // ref only.
if (AndroidBitmap_unlockPixels(env, j_argb8888_bitmap) < 0) {
LOGE("Invoke AndroidBitmap_unlockPixels() failed!");
return c_rgba;
}
return c_rgba;
}
jboolean ARGB888Bitmap2RGBA(JNIEnv *env, jobject j_argb8888_bitmap,
cv::Mat *c_rgba) {
// Convert the android bitmap(ARGB8888) to the OpenCV RGBA image. Actually,
// the data layout of ARGB8888 is R, G, B, A, it's the same as CV RGBA image,
// so it is unnecessary to do the conversion of color format, check
// https://developer.android.com/reference/android/graphics/Bitmap.Config#ARGB_8888
// to get the more details about Bitmap.Config.ARGB8888
*c_rgba = CreateZeroCopyRGBAFromBitmap(env, j_argb8888_bitmap);
if (c_rgba->empty()) {
return JNI_FALSE;
}
return JNI_TRUE;
}
jboolean ARGB888Bitmap2BGR(JNIEnv *env, jobject j_argb8888_bitmap,
cv::Mat *c_bgr) {
cv::Mat c_rgba;
if (!ARGB888Bitmap2RGBA(env, j_argb8888_bitmap, &c_rgba)) {
return JNI_FALSE;
}
// TODO: Use the neon instruction to optimize this conversion.
// COLOR_RGBA2BGR will allocate memories for new mat.
cv::cvtColor(c_rgba, *(c_bgr), cv::COLOR_RGBA2BGR);
return JNI_TRUE;
}
jboolean RGBA2ARGB888Bitmap(JNIEnv *env, jobject j_argb8888_bitmap,
const cv::Mat &c_rgba) {
AndroidBitmapInfo j_bitmap_info;
if (AndroidBitmap_getInfo(env, j_argb8888_bitmap, &j_bitmap_info) < 0) {
LOGE("Invoke AndroidBitmap_getInfo() failed!");
return JNI_FALSE;
}
void *j_bitmap_pixels;
if (AndroidBitmap_lockPixels(env, j_argb8888_bitmap, &j_bitmap_pixels) < 0) {
LOGE("Invoke AndroidBitmap_lockPixels() failed!");
return JNI_FALSE;
}
// no copied, but point to bitmap data.
cv::Mat j_bitmap_im(static_cast<int>(j_bitmap_info.height),
static_cast<int>(j_bitmap_info.width), CV_8UC4,
j_bitmap_pixels);
// TODO: Use zero copy operation or neon to boost performance.
c_rgba.copyTo(j_bitmap_im);
if (AndroidBitmap_unlockPixels(env, j_argb8888_bitmap) < 0) {
LOGE("Invoke AndroidBitmap_unlockPixels() failed!");
return JNI_FALSE;
}
return JNI_TRUE;
}
jboolean BGR2ARGB888Bitmap(JNIEnv *env, jobject j_argb8888_bitmap,
const cv::Mat &c_bgr) {
if (c_bgr.empty()) {
return JNI_FALSE;
}
cv::Mat c_rgba;
cv::cvtColor(c_bgr, c_rgba, cv::COLOR_BGR2RGBA);
return RGBA2ARGB888Bitmap(env, j_argb8888_bitmap, c_rgba);
}
– 测试代码
//
// Created by admin on 2023/4/14.
//
#include <jni.h>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <android/bitmap.h>
#include <android/log.h>
extern "C" {
// bitmap --> cv::Mat
bool BitmapToMatrix(JNIEnv * env, jobject obj_bitmap, cv::Mat & matrix) {
void * bitmapPixels; // Save picture pixel data
AndroidBitmapInfo bitmapInfo; // Save picture parameters
AndroidBitmap_getInfo(env, obj_bitmap, &bitmapInfo); // Get picture parameters
//Only ARGB_8888 and RGB_565 are supported
if (bitmapInfo.format != ANDROID_BITMAP_FORMAT_RGBA_8888
&& bitmapInfo.format != ANDROID_BITMAP_FORMAT_RGB_565)
{
__android_log_print(ANDROID_LOG_INFO, "ncnn", "BitmapToMatrix err--1");
return false;
}
AndroidBitmap_lockPixels(env, obj_bitmap, &bitmapPixels); // Get picture pixels (lock memory block)
if (not bitmapPixels)
{
__android_log_print(ANDROID_LOG_INFO, "ncnn", "BitmapToMatrix err--2");
return false;
}
if (bitmapInfo.format == ANDROID_BITMAP_FORMAT_RGBA_8888) {
cv::Mat tmp(bitmapInfo.height, bitmapInfo.width, CV_8UC4, bitmapPixels); // Establish temporary mat
tmp.copyTo(matrix); // Copy to target matrix
} else {
cv::Mat tmp(bitmapInfo.height, bitmapInfo.width, CV_8UC2, bitmapPixels);
cv::cvtColor(tmp, matrix, cv::COLOR_BGR5652RGB);
}
//convert RGB to BGR
cv::cvtColor(matrix,matrix,cv::COLOR_RGB2BGR);
AndroidBitmap_unlockPixels(env, obj_bitmap); // Unlock
return true;
}
//bitmap --> cv::Mat
bool nativeBitmapToMat(JNIEnv *env, jobject bitmap, cv::Mat& img) {
AndroidBitmapInfo info;
void* pixels;
// 获取 Bitmap 的信息与像素数据
if (AndroidBitmap_getInfo(env, bitmap, &info) != ANDROID_BITMAP_RESULT_SUCCESS ||
AndroidBitmap_lockPixels(env, bitmap, &pixels) != ANDROID_BITMAP_RESULT_SUCCESS) {
__android_log_print(ANDROID_LOG_INFO, "ncnn", "nativeBitmapToMat err");
return false;
}
// 创建 Mat 对象并拷贝像素数据
img.create(info.height, info.width, CV_8UC4);
memcpy(img.data, pixels, info.stride * info.height);
// cv::imwrite("bitmap2mat_2.jpg", img);
// 解锁像素数据，释放资源
AndroidBitmap_unlockPixels(env, bitmap);
return true;
}
JNIEXPORT jstring JNICALL Java_com_example_ad_1test_MainActivity_detectOneImage(JNIEnv* env, jobject thiz, jlong ptr, jobject bitmap) {
cv::Mat img_tt;
BitmapToMatrix(env, bitmap, img_tt);
__android_log_print(ANDROID_LOG_INFO, "ncnn", "BitmapToMatrix 转换完成");
cv::Mat img_tt2;
nativeBitmapToMat(env, bitmap, img_tt2);
__android_log_print(ANDROID_LOG_INFO, "ncnn", "nativeBitmapToMat 转换完成");
std::string result = "reinterpret_cast<NcnnYolov5lite*>(ptr)->detectOneImage(img_tt)转换完成";
return env->NewStringUTF(result.c_str());
};
}
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