Android平台OpenCV入门

一、导入OpenCV

别忘记把libopencv_java3.so添加进来。

二、初始化

OpenCVLoader.initDebug();

三、常用方法

1. CvType 数据类型

以CV_64FC2为例，64指64位，F指浮点数，C指通道，2为2通道。

数值	具体类型	取值范围
CV_8U	8 位无符号整数	（0……255）
CV_8S	8 位符号整数	（-128……127）
CV_16U	16 位无符号整数	（0……65535）
CV_16S	16 位符号整数	（-32768……32767）
CV_32S	32 位符号整数	（-2147483648……2147483647）
CV_32F	32 位浮点数	（-FLT_MAX ………FLT_MAX，INF，NAN)
CV_64F	64 位浮点数	（-DBL_MAX ……….DBL_MAX，INF，NAN)

public static final int CV_8UC1 = CV_8UC(1);
public static final int CV_8UC2 = CV_8UC(2);
public static final int CV_8UC3 = CV_8UC(3);
public static final int CV_8UC4 = CV_8UC(4);
public static final int CV_8SC1 = CV_8SC(1);
public static final int CV_8SC2 = CV_8SC(2);
public static final int CV_8SC3 = CV_8SC(3);
public static final int CV_8SC4 = CV_8SC(4);
public static final int CV_16UC1 = CV_16UC(1);
public static final int CV_16UC2 = CV_16UC(2);
public static final int CV_16UC3 = CV_16UC(3);
public static final int CV_16UC4 = CV_16UC(4);
public static final int CV_16SC1 = CV_16SC(1);
public static final int CV_16SC2 = CV_16SC(2);
public static final int CV_16SC3 = CV_16SC(3);
public static final int CV_16SC4 = CV_16SC(4);
public static final int CV_32SC1 = CV_32SC(1);
public static final int CV_32SC2 = CV_32SC(2);
public static final int CV_32SC3 = CV_32SC(3);
public static final int CV_32SC4 = CV_32SC(4);
public static final int CV_32FC1 = CV_32FC(1);
public static final int CV_32FC2 = CV_32FC(2);
public static final int CV_32FC3 = CV_32FC(3);
public static final int CV_32FC4 = CV_32FC(4);
public static final int CV_64FC1 = CV_64FC(1);
public static final int CV_64FC2 = CV_64FC(2);
public static final int CV_64FC3 = CV_64FC(3);
public static final int CV_64FC4 = CV_64FC(4);

2. Mat的加载方式

2.1 文件形式加载——Imgcodecs.imread

Mat mat = Imgcodecs.imread(filename); // 默认转成bgr格式，即Imgcodecs.IMREAD_COLOR
Mat mat = Imgcodecs.imread(filename, flags);

参数：filename
输入可为相对路径也可为绝对路径，自动通过后缀名识别文件的格式。

支持读取的图像格式有：

Windows bitmaps - *.bmp, *.dib (always supported)
JPEG files - *.jpeg, *.jpg, *.jpe (see the Note section)
JPEG 2000 files - *.jp2 (see the Note section)
Portable Network Graphics - *.png (see the Note section)
WebP - *.webp (see the Note section)
Portable image format - *.pbm, *.pgm, *.ppm *.pxm, *.pnm (always supported)
PFM files - *.pfm (see the Note section)
Sun rasters - *.sr, *.ras (always supported)
TIFF files - *.tiff, *.tif (see the Note section)
OpenEXR Image files - *.exr (see the Note section)
Radiance HDR - *.hdr, *.pic (always supported)
Raster and Vector geospatial data supported by GDAL (see the Note section)

**参数：**flags，当不写时，默认为Imgcodecs.IMREAD_COLOR

值	枚举名	定义	解释
-1	IMREAD_UNCHANGED	If set, return the loaded image as is (with alpha channel, otherwise it gets cropped). Ignore EXIF orientation.	如果设置，则按原样返回加载的图像（使用Alpha通道，否则会被裁剪）
0	IMREAD_GRAYSCALE	If set, always convert image to the single channel grayscale image (codec internal conversion).	如果设置，则始终将图像转换为单通道灰度图像（编解码器内部转换）
1	IMREAD_COLOR	If set, always convert image to the 3 channel BGR color image.	如果设置，请始终将图像转换为3通道BGR彩色图像
2	IMREAD_ANYDEPTH	If set, return 16-bit/32-bit image when the input has the corresponding depth, otherwise convert it to 8-bit.	如果设置，则在输入具有相应深度时返回16位/ 32位图像，否则将其转换为8位
4	IMREAD_ANYCOLOR	If set, the image is read in any possible color format.	如果设置，则以任何可能的颜色格式读取图像
8	IMREAD_LOAD_GDAL	If set, use the gdal driver for loading the image.	如果设置，使用gdal驱动程序加载图像
16	IMREAD_REDUCED_GRAYSCALE_2	If set, always convert image to the single channel grayscale image and the image size reduced 1/2.	如果设置，则始终将图像转换为单通道灰度图像，图像尺寸减小1/2
17	IMREAD_REDUCED_COLOR_2	If set, always convert image to the 3 channel BGR color image and the image size reduced 1/2.	如果设置，则始终将图像转换为3通道BGR彩色图像，图像尺寸减小1/2
32	IMREAD_REDUCED_GRAYSCALE_4	If set, always convert image to the single channel grayscale image and the image size reduced 1/4.	如果设置，则始终将图像转换为单通道灰度图像，图像尺寸减小1/4
33	IMREAD_REDUCED_COLOR_4	If set, always convert image to the 3 channel BGR color image and the image size reduced 1/4.	如果设置，则始终将图像转换为3通道BGR彩色图像，图像尺寸减小1/4
64	IMREAD_REDUCED_GRAYSCALE_8	If set, always convert image to the single channel grayscale image and the image size reduced 1/8.	如果设置，则始终将图像转换为单通道灰度图像，图像尺寸减小1/8
65	IMREAD_REDUCED_COLOR_8	If set, always convert image to the 3 channel BGR color image and the image size reduced 1/8.	如果设置，则始终将图像转换为3通道BGR彩色图像，图像尺寸减小1/8
128	IMREAD_IGNORE_ORIENTATION	If set, do not rotate the image according to EXIF’s orientation flag.	如果设置，请不要根据EXIF的方向标志旋转图像

2.2 数组形式导入——mat.put

Mat mat = new Mat(height, width, CvType.CV_8UC1);
mat.put(0,0,bytes);

根据数组的存储格式和宽高导入，格式见前文 CvType 数据类型

2.3 YUV数组转mat（图像格式转换）——Imgproc.cvtColor

public static Mat nv21Mat(byte[] nv21, int width, int height) {Mat nv21Mat = new Mat(height*3/2,width,CvType.CV_8UC1);//按单通道位图构建matint re =  nv21Mat.put(0,0,nv21);Mat mat = new Mat();Imgproc.cvtColor(nv21Mat , mat, Imgproc.COLOR_YUV2BGR_NV21);return mat;
}

yuv格式的数组要先按单通道位图构建mat，再通过Imgproc.cvtColor()进行格式转换。

3. 存位图——Imgcodecs.imwrite

//存取16位单通道图
public static void saveShortToPng(short[] shortBytes, int width, int height, String path) {String mPath = path;Mat mat = new Mat(height, width, CvType.CV_16UC1);mat.put(0,0,shortBytes);Imgcodecs.imwrite(mPath,mat);
}

可根据文件名的后缀自行保存。

4. 图像缩放——Imgproc.resize

public static byte[] resizeByte(byte[] sBytes, int width, int height) {byte[] bytes = new byte[sBytes.length];System.arraycopy(sBytes,0,bytes,0,sBytes.length);Mat src = new Mat(height, width, CvType.CV_8UC1);src.put(0,0,bytes);Imgproc.resize(src, src, new Size(src.width()*0.5, src.height()*0.5));byte[] dBytes = new byte[width/2 * height/2];src.get(0,0,dBytes);return dBytes;
}

5. 抠图——mat.submat

public static void saveFace(byte[] nv21, int[] position, int width, int height, String path){//YUV 转 MatMat matNv21 = new Mat(height*3/2,width,CvType.CV_8UC1);//按单通道位图构建matint re =  matNv21.put(0,0,nv21);Mat matBgr = new Mat();Imgproc.cvtColor(matNv21 , matBgr, Imgproc.COLOR_YUV2BGR_NV21);//nv21 to bgr//Android自带也有个Rect方法，要区分开org.opencv.core.Rect rect = new org.opencv.core.Rect(position[0], position[1], position[2], position[3]);//抠图Mat sub = matBgr.submat(rect); Mat mat = new Mat();Size size = new Size(position[2],position[3]);Imgproc.resize(sub, mat, size);//将人脸进行截图并保存String mPath = path;Imgcodecs.imwrite(mPath,mat);
}

6. 图像旋转

/**
* 图像旋转
*/
public static byte[] rotateByte(byte[] sBytes, int width, int height) {byte[] dBytes = new byte[sBytes.length];Mat mat = new Mat(height, width, CvType.CV_8UC1);//单通道位图mat.put(0,0,sBytes);Core.transpose(mat,mat);// 转置（行列互换），即顺时针旋转90度且左右镜像Core.flip(mat, mat, 1);// 1：左右镜像；0：上下镜像；-1：旋转180度mat.get(0,0,dBytes);return dBytes;
}