图像格式转化在人脸识别应用中的实践ArcFace 2.0 API目前支持多种图像格式：BGR24、NV21、NV12、I

ArcFace 2.0 API目前支持多种图像格式：BGR24、NV21、NV12、I420、YUYV（Android、IOS只支持其中的部分）。接下来将开始介绍这几种图像格式以及部分转换方式。

一、相关图像颜色空间介绍

1. RGB颜色空间

RGB颜色空间以Red、Green、Blue三种基本色为基础，进行不同程度的叠加，产生丰富而广泛的颜色，所以俗称三基色模式。常见的RGB格式有：RGB_565、RGB_888、ARGB_8888、ARGB_4444等。

2. YUV颜色空间

在YUV颜色空间中，Y用来表示亮度，U和V用来表示色度。常见的YUV格式有以下几大类： planar: Y、U、V全部连续存储，如I420、YV12 packed: Y、U、V交叉存储，如YUYV semi-planar: Y连续存储，U、V交叉存储，如NV21、NV12

二、相关图像格式介绍

1. BGR24图像格式

BGR24图像格式是一种采用24bpp(bit per pixel)的格式。每个颜色通道B、G、R各占8bpp。排列方式如：

B G R  B G R  B G R  B G R  B G R  B G R  B G R  B G R 

B G R  B G R  B G R  B G R  B G R  B G R  B G R  B G R 

B G R  B G R  B G R  B G R  B G R  B G R  B G R  B G R 

B G R  B G R  B G R  B G R  B G R  B G R  B G R  B G R

2. NV21图像格式

NV21图像格式属于 YUV颜色空间中的YUV420SP格式，每四个Y分量共用一组U分量和V分量，Y连续排序，U与V交叉排序。排列方式如：

Y Y  Y Y  Y Y  Y Y
Y Y  Y Y  Y Y  Y Y

Y Y  Y Y  Y Y  Y Y
Y Y  Y Y  Y Y  Y Y

V U  V U  V U  V U

V U  V U  V U  V U

3. NV12图像格式

NV12图像格式属于 YUV颜色空间中的YUV420SP格式，每四个Y分量共用一组U分量和V分量，Y连续排序，U与V交叉排序（NV12和NV21只是U与V的位置相反）。排列方式如：

Y Y  Y Y  Y Y  Y Y
Y Y  Y Y  Y Y  Y Y

Y Y  Y Y  Y Y  Y Y
Y Y  Y Y  Y Y  Y Y

U V  U V  U V  U V

U V  U V  U V  U V

4. I420图像格式

I420图像格式属于 YUV颜色空间中的YUV420P格式，每四个Y分量共用一组U分量和V分量，Y、U、V各自连续排序。（为了便于说明Y、U、V的共用关系，U和V都未换行）排列方式如：

Y Y  Y Y  Y Y  Y Y
Y Y  Y Y  Y Y  Y Y

Y Y  Y Y  Y Y  Y Y
Y Y  Y Y  Y Y  Y Y

U  U  U  U  U  U  U  U 
V  V  V  V  V  V  V  V

5. YV12图像格式

YV12图像格式属于 YUV颜色空间中的YUV420P格式，每四个Y分量共用一组U分量和V分量，Y、U、V各自连续排序（为了便于说明Y、U、V的共用关系，U和V都未换行）（YV12和I420只是U与V的位置相反）。排列方式如：

Y Y  Y Y  Y Y  Y Y
Y Y  Y Y  Y Y  Y Y

Y Y  Y Y  Y Y  Y Y
Y Y  Y Y  Y Y  Y Y

V  V  V  V  V  V  V  V 
U  U  U  U  U  U  U  U

6. YUYV图像格式

YUYV图像格式属于 YUV颜色空间中的YUV422格式，每两个Y分量共用一组U分量和V分量，Y、U、V交叉排序。排列方式如：

Y U Y V   Y U Y V  Y U Y V  Y U Y V

Y U Y V   Y U Y V  Y U Y V  Y U Y V

Y U Y V   Y U Y V  Y U Y V  Y U Y V

Y U Y V   Y U Y V  Y U Y V  Y U Y V

三、图像格式转换

由于图像的格式多种多样，转换的方法也不胜枚举，只要了解了YUV和RGB数据的排列方式，自己编写图像转换代码也花不了多少时间。以下列出部分的图像转换的Java代码供参考。

1. 从`Bitmap`中获取`ARGB_8888`图像格式数据(Android平台)

Bitmap支持多种格式：ALPHA_8，RGB_565，ARGB_4444，ARGB_8888，RGBA_F16，HARDWARE。我们目前主要选择ARGB_8888进行格式转换。我们可使用Bitmap类中的 public void getPixels(@ColorInt int[] pixels, int offset, int stride, int x, int y, int width, int height) 方法获取int[]类型的argb数据或 public void copyPixelsToBuffer (Buffer dst)方法获取byte[]类型的ARGB_8888数据。

2. `ARGB_8888`转换为`BGR_24`

举个例子，对于4x2的图片，ARGB_8888格式内容为：

A1 R1 G1 B1  A2 R2 G2 B2  A3 R3 G3 B3  A4 R4 G4 B4
A5 R5 G5 B5  A6 R6 G6 B6  A7 R7 G7 B7  A8 R8 G8 B8

那么若需要转化为BGR_24，内容将变成：

B1 G1 R1  B2 G2 R2  B3 G3 R3  B4 G4 R4
B5 G5 R5  B6 G6 R6  B7 G7 R7  B8 G8 R8

BGR_24内容为3个byte一组，ARGB_8888内容为4个byte一组。因此，对于第一组ARGB_8888(A1 R1 G1 B1)和第一组BGR_24(B1 G1 R1)，其对应关系为：

bgr24[0] = argb8888[3];
bgr24[1] = argb8888[2];
bgr24[2] = argb8888[1];

对应的转换代码：

    public static byte[] argb8888ToBgr24(byte[] argb8888) {
        if (argb8888 == null){
            throw new IllegalArgumentException("invalid image params!");
        }
        int groupNum = argb8888.length / 4;
        byte[] bgr24 = new byte[groupNum * 3];
        int bgr24Index = 0;
        int argb8888Index = 0;
        for (int i = 0; i < groupNum; i++) {
            bgr24[bgr24Index] = argb8888[argb8888Index + 2];
            bgr24[bgr24Index + 1] = argb8888[argb8888Index + 1];
            bgr24[bgr24Index + 2] = argb8888[argb8888Index];
            bgr24Index += 3;
            argb8888Index += 4;
        }
        return bgr24;
    }

3. `ARGB_8888`转换为`NV21`

rgb转yuv的算法：

int y = (66 * r + 129 * g + 25 * b + 128 >> 8) + 16;
int u = (-38 * r - 74 * g + 112 * b + 128 >> 8) + 128;
int v = (112 * r - 94 * g - 18 * b + 128 >> 8) + 128;

转换方法：

int[]类型的ARGB_8888数据转换为NV21：

    private static byte[] argbToNv21(int[] argb, int width, int height) {
        if (argb == null || argb.length == 0 || width * height != argb.length) {
            throw new IllegalArgumentException("invalid image params!");
        }
        int yIndex = 0;
        int uvIndex = width * height;
        int argbIndex = 0;
        byte[] nv21 = new byte[width * height * 3 / 2];
        for (int j = 0; j < height; ++j) {
            for (int i = 0; i < width; ++i) {
                //对于int型color数据，格式为0xAARRGGBB，可进行与运算后移位取对应A R G B，
                //但是该YUV转换公式中不需要ALPHA，因此我们只需要取 R G B 即可。
                int r = (argb[argbIndex] & 0xFF0000) >> 16;
                int g = (argb[argbIndex] & 0x00FF00) >> 8;
                int b = argb[argbIndex] & 0x0000FF;
                //获取该像素点的R G B，并转换为Y U V，但byte范围是0x00~0xFF，因此在赋值时还需进行判断
                int y = (66 * r + 129 * g + 25 * b + 128 >> 8) + 16;
                nv21[yIndex++] = (byte) (y < 0 ? 0 : (y > 0xFF ? 0xFF : y));
                if ((j & 1) == 0 && (argbIndex & 1) == 0 && uvIndex < nv21.length - 2) {
                    int u = (-38 * r - 74 * g + 112 * b + 128 >> 8) + 128;
                    int v = (112 * r - 94 * g - 18 * b + 128 >> 8) + 128;
                    nv21[uvIndex++] = (byte) (v < 0 ? 0 : (v > 0xFF ? 0xFF : v));
                    nv21[uvIndex++] = (byte) (u < 0 ? 0 : (u > 0xFF ? 0xFF : u));
                }
                ++argbIndex;
            }
        }
        return nv21;
    }

byte[]类型的ARGB_8888数据转换为NV21(原理同方法1)：

   private static byte[] argbToNv21(byte[] argb, int width, int height) {
        if (argb == null || argb.length == 0 || width * height * 4 != argb.length) {
            throw new IllegalArgumentException("invalid image params!");
        }
        int yIndex = 0;
        int uvIndex = width * height;
        int argbIndex = 0;
        byte[] nv21 = new byte[width * height * 3 / 2];
        for (int j = 0; j < height; ++j) {
            for (int i = 0; i < width; ++i) {
                argbIndex++;
                int r = argb[argbIndex++];
                int g = argb[argbIndex++];
                int b = argb[argbIndex++];
                r &= 0x000000FF;
                g &= 0x000000FF;
                b &= 0x000000FF;
                int y = ((66 * r + 129 * g + 25 * b + 128 >> 8) + 16);
                nv21[yIndex++] = (byte) (y > 0xFF ? 0xFF : (y < 0 ? 0 : y));
                if ((j & 1) == 0 && ((argbIndex >> 2) & 1) == 0 && uvIndex < nv21.length - 2) {
                    int u = ((-38 * r - 74 * g + 112 * b + 128 >> 8) + 128);
                    int v = ((112 * r - 94 * g - 18 * b + 128 >> 8) + 128);
                    nv21[uvIndex++] = (byte) (v > 0xFF ? 0xFF : (v < 0 ? 0 : v));
                    nv21[uvIndex++] = (byte) (u > 0xFF ? 0xFF : (u < 0 ? 0 : u));
                }
            }
        }
        return nv21;
    }

4. `NV21`转换为`BGR24`

yuv转rgb算法：

int r = (int) ((y & 0xFF) + 1.4075 * ((v & 0xFF) - 128));
int g = (int) ((y & 0xFF) - 0.3455 * ((u & 0xFF) - 128) - 0.7169 * ((v & 0xFF) - 128));
int b = (int) ((y & 0xFF) + 1.779 * ((u & 0xFF) - 128));

转换方法：

    private static byte[] nv21ToBgr24(byte[] nv21, int width, int height) {
        if (nv21 == null || nv21.length == 0 || width * height * 3 / 2 != nv21.length) {
            throw new IllegalArgumentException("invalid image params!");
        }
        byte[] bgr24 = new byte[width * height * 3];
        int bgrLineSize = width * 3;
        //偶数行的bgr数据下标
        int evenLineBgrIndex = 0;
        //奇数行的bgr数据下标
        int oddLineBgrIndex = bgrLineSize;
        //当前一行y数据最左边的下标
        int yLineStart = 0;
        //uv数据的下标
        int uvIndex = width * height;
        //由于NV21的共用关系，每2行做一次转换
        for (int i = 0; i < height; i += 2) {
            for (int widthOffset = 0; widthOffset < width; widthOffset++) {
                byte v = nv21[uvIndex];
                byte u = nv21[uvIndex + 1];
                byte yEven = nv21[yLineStart + widthOffset];
                byte yOdd = nv21[yLineStart + width + widthOffset];
                //偶数行YUV转RGB
                int r, g, b;
                r = (int) ((yEven & 0xFF) + 1.4075 * ((v & 0xFF) - 128));
                g = (int) ((yEven & 0xFF) - 0.3455 * ((u & 0xFF) - 128) - 0.7169 * ((v & 0xFF) - 128));
                b = (int) ((yEven & 0xFF) + 1.779 * ((u & 0xFF) - 128));
                r = r < 0 ? 0 : r > 0xFF ? 0xFF : r;
                g = g < 0 ? 0 : g > 0xFF ? 0xFF : g;
                b = b < 0 ? 0 : b > 0xFF ? 0xFF : b;
                bgr24[evenLineBgrIndex++] = (byte) b;
                bgr24[evenLineBgrIndex++] = (byte) g;
                bgr24[evenLineBgrIndex++] = (byte) r;
                //奇数行YUV转RGB
                r = (int) ((yOdd & 0xFF) + 1.4075 * ((v & 0xFF) - 128));
                g = (int) ((yOdd & 0xFF) - 0.3455 * ((u & 0xFF) - 128) - 0.7169 * ((v & 0xFF) - 128));
                b = (int) ((yOdd & 0xFF) + 1.779 * ((u & 0xFF) - 128));
                r = r < 0 ? 0 : r > 0xFF ? 0xFF : r;
                g = g < 0 ? 0 : g > 0xFF ? 0xFF : g;
                b = b < 0 ? 0 : b > 0xFF ? 0xFF : b;
                bgr24[oddLineBgrIndex++] = (byte) b;
                bgr24[oddLineBgrIndex++] = (byte) g;
                bgr24[oddLineBgrIndex++] = (byte) r;
                //每两个y将uv下标增1
                if ((widthOffset & 1) == 1) {
                    uvIndex += 2;
                }
            }
            //由于在内层循环中已经做过width * 3次自增，所以外层循环中只需要增加一行
            evenLineBgrIndex += bgrLineSize;
            oddLineBgrIndex += bgrLineSize;
            //y增2行
            yLineStart += width * 2;
        }
        return bgr24;
    }

5. `NV12`和`NV21`的互换

NV21和NV12只是U与V的数据位置不同，因此，NV21转换为NV12的代码同样适用于NV12转换为NV21。可参考如下代码：

public static byte[] nv21ToNv12(byte[] nv21, int width, int height) {
        if (nv21 == null || nv21.length == 0 || width * height * 3 / 2 != nv21.length) {
            throw new IllegalArgumentException("invalid image params!");
        }
        final int ySize = width * height;
        int totalSize = width * height * 3 / 2;

        byte[] nv12 = new byte[nv21.length];
        //复制Y
        System.arraycopy(nv21, 0, nv12, 0, ySize);
        //UV互换
        for (int uvIndex = ySize; uvIndex < totalSize; uvIndex += 2) {
            nv12[uvIndex] = nv21[uvIndex + 1];
            nv12[uvIndex + 1] = nv21[uvIndex];
        }
        return nv12;
    }

6. `NV21`转`YV12`

NV21转化为YV12的过程主要是将其UV数据的交叉排序修改为连续排序。可参考如下代码：

public static byte[] nv21ToYv12(byte[] nv21, int width, int height) {
        if (nv21 == null || nv21.length == 0 || width * height * 3 / 2 != nv21.length) {
            throw new IllegalArgumentException("invalid image params!");
        }
        final int ySize = width * height;
        int totalSize = width * height * 3 / 2;
        byte[] yv12 = new byte[nv21.length];
        int yv12UIndex = ySize;
        int yv12VIndex = ySize * 5 / 4;
        //复制Y
        System.arraycopy(nv21, 0, yv12, 0, ySize);
        //复制UV
        for (int uvIndex = ySize; uvIndex < totalSize; uvIndex += 2) {
            yv12[yv12UIndex++] = nv21[uvIndex];
            yv12[yv12VIndex++] = nv21[uvIndex + 1];
        }
        return yv12;
    }

7. `YUYV`转`NV12`

在YUYV格式中，两个Y共用一组U和V，而NV12是四个Y共用一组U和V，因此，这是一个YUV422转YUV420的过程，需要舍弃一半的U和V。可参考如下代码：


    public static byte[] yuyvToNv12(byte[] yuyv, int width, int height) {
        if (yuyv == null || yuyv.length == 0) {
            throw new IllegalArgumentException("invalid image params!");
        }
        int ySize = yuyv.length / 2;
        byte[] nv12 = new byte[yuyv.length * 3 / 4];
        int nv12YIndex = 0;
        int nv12UVIndex = ySize;
        boolean copyUV = false;
        int lineDataSize = width * 2;
        for (int i = 0, yuyvIndex = 0; i < height; i++, yuyvIndex += lineDataSize) {
            if (copyUV) {
                for (int lineOffset = 0; lineOffset < lineDataSize; lineOffset += 4) {
                    //复制Y
                    nv12[nv12YIndex++] = yuyv[yuyvIndex + lineOffset];
                    nv12[nv12YIndex++] = yuyv[yuyvIndex + lineOffset + 2];
                    //复制UV
                    nv12[nv12UVIndex++] = yuyv[yuyvIndex + lineOffset + 1];
                    nv12[nv12UVIndex++] = yuyv[yuyvIndex + lineOffset + 3];
                }
            } else {
                for (int lineOffset = 0; lineOffset < lineDataSize; lineOffset += 4) {
                    //复制Y
                    nv12[nv12YIndex++] = yuyv[yuyvIndex + lineOffset];
                    nv12[nv12YIndex++] = yuyv[yuyvIndex + lineOffset + 2];
                }
            }
            copyUV = !copyUV;
        }
        return nv12;
    }

8. `I420`和`YV12`的互换

I420和YV12只是U与V的数据位置不同，因此，I420转换为YV12的代码同样适用于YV12转换为I420。可参考如下代码：

public static byte[] i420ToYv12(byte[] i420) {
        if (i420 == null || i420.length == 0 || i420.length % 6 != 0) {
            throw new IllegalArgumentException("invalid image params!");
        }
        int ySize = i420.length * 2 / 3;
        int uvSize = i420.length / 6;
        byte[] yv12 = new byte[i420.length];
        //复制Y
        System.arraycopy(i420, 0, yv12, 0, ySize);
        //UV互换
        System.arraycopy(i420, ySize, yv12, ySize + uvSize, uvSize);
        System.arraycopy(i420, ySize + uvSize, yv12, ySize, uvSize);
        return yv12;
    }

9. `I420`转换为`YUYV`

I420和YUYV相比，I420的U和V只有YUYV的一半，这是一个YUV420转YUV422的过程，缺损的数据只能通过复用U和V弥补。

public static byte[] i420ToYuyv(byte[] i420, int width, int height) {
        if (i420 == null || i420.length == 0 || i420.length != width * height * 3 / 2) {
            throw new IllegalArgumentException("invalid image params!");
        }
        byte[] yuyv = new byte[width * height * 2];
        int yuyvLineSize = width * 2;
        int i420YIndex = 0;
        int i420UIndex = width * height;
        int i420VIndex = width * height * 5 / 4;
        int yuyvLineStart = 0;
        for (int i = 0; i < height; i += 2) {
            for (int lineOffset = 0; lineOffset < yuyvLineSize; lineOffset += 4) {
                byte u = i420[i420UIndex++];
                byte v = i420[i420VIndex++];
                //偶数行数据赋值
                int yuyvOffset = yuyvLineStart + lineOffset;
                yuyv[yuyvOffset] = i420[i420YIndex];
                yuyv[yuyvOffset + 1] = u;
                yuyv[yuyvOffset + 2] = i420[i420YIndex + 1];
                yuyv[yuyvOffset + 3] = v;
                //奇数行数据赋值
                int yuyvNextLineOffset = yuyvLineStart + yuyvLineSize + lineOffset;
                yuyv[yuyvNextLineOffset] = i420[i420YIndex + width];
                yuyv[yuyvNextLineOffset + 1] = u;
                yuyv[yuyvNextLineOffset + 2] = i420[i420YIndex + width + 1];
                yuyv[yuyvNextLineOffset + 3] = v;

                i420YIndex += 2;
            }
            i420YIndex += width;
            yuyvLineStart += (width << 2);
        }
        return yuyv;
    }

四、图像裁剪

与格式转换相同，只要了解的图像的排列方式，图像的裁剪也并不困难。本文提供一种RGB颜色空间的图像裁剪和一种YUV颜色空间的图像裁剪。

1. 裁剪NV21

public static byte[] i420ToYv12(byte[] i420) {
        if (i420 == null || i420.length == 0 || i420.length % 6 != 0) {
            throw new IllegalArgumentException("invalid image params!");
        }
        int ySize = i420.length * 2 / 3;
        int uvSize = i420.length / 6;
        byte[] yv12 = new byte[i420.length];
        //复制Y
        System.arraycopy(i420, 0, yv12, 0, ySize);
        //UV互换
        System.arraycopy(i420, ySize, yv12, ySize + uvSize, uvSize);
        System.arraycopy(i420, ySize + uvSize, yv12, ySize, uvSize);
        return yv12;
    }

9. `I420`转换为`YUYV`

I420和YUYV相比，I420的U和V只有YUYV的一半，这是一个YUV420转YUV422的过程，缺损的数据只能通过复用U和V弥补。

public static byte[] i420ToYuyv(byte[] i420, int width, int height) {
        if (i420 == null || i420.length == 0 || i420.length != width * height * 3 / 2) {
            throw new IllegalArgumentException("invalid image params!");
        }
        byte[] yuyv = new byte[width * height * 2];
        int yuyvLineSize = width * 2;
        int i420YIndex = 0;
        int i420UIndex = width * height;
        int i420VIndex = width * height * 5 / 4;
        int yuyvLineStart = 0;
        for (int i = 0; i < height; i += 2) {
            for (int lineOffset = 0; lineOffset < yuyvLineSize; lineOffset += 4) {
                byte u = i420[i420UIndex++];
                byte v = i420[i420VIndex++];
                //偶数行数据赋值
                int yuyvOffset = yuyvLineStart + lineOffset;
                yuyv[yuyvOffset] = i420[i420YIndex];
                yuyv[yuyvOffset + 1] = u;
                yuyv[yuyvOffset + 2] = i420[i420YIndex + 1];
                yuyv[yuyvOffset + 3] = v;
                //奇数行数据赋值
                int yuyvNextLineOffset = yuyvLineStart + yuyvLineSize + lineOffset;
                yuyv[yuyvNextLineOffset] = i420[i420YIndex + width];
                yuyv[yuyvNextLineOffset + 1] = u;
                yuyv[yuyvNextLineOffset + 2] = i420[i420YIndex + width + 1];
                yuyv[yuyvNextLineOffset + 3] = v;

                i420YIndex += 2;
            }
            i420YIndex += width;
            yuyvLineStart += (width << 2);
        }
        return yuyv;
    }

四、图像裁剪

与格式转换相同，只要了解的图像的排列方式，图像的裁剪也并不困难。本文提供一种RGB颜色空间的图像裁剪和一种YUV颜色空间的图像裁剪。

1. 裁剪NV21或NV12

public static byte[] cropYuv420sp(byte[] yuv420sp, int width, int height, int left, int top, int right, int bottom) {
        if (yuv420sp == null || yuv420sp.length == 0 || width * height * 3 / 2 != yuv420sp.length) {
            throw new IllegalArgumentException("invalid image params!");
        }
        if (left < 0 || top < 0 || right > width || bottom > height) {
            throw new IllegalArgumentException("rect out of bounds!");
        }
        if (right < left || bottom < top) {
            throw new IllegalArgumentException("invalid rect!");
        }
        if (((right - left) & 1) == 1 || ((bottom - top) & 1) == 1) {
            throw new IllegalArgumentException("yuv420sp width and height must be even!");
        }
        if ((left & 1 )== 1){
            throw new IllegalArgumentException("yuv420sp crop left borderIndex and right borderIndex must be even!");
        }
        int cropImageWidth = right - left;
        int cropImageHeight = bottom - top;
        byte[] cropYuv420sp = new byte[cropImageWidth * cropImageHeight * 3 / 2];

        //复制Y
        int originalYLineStart = top * width;
        int targetYIndex = 0;

        //复制UV
        int originalUVLineStart = width * height + top * width / 2;
        int targetUVIndex = cropImageWidth * cropImageHeight;
        for (int i = top; i < bottom; i++) {
            System.arraycopy(yuv420sp, originalYLineStart + left, cropYuv420sp, targetYIndex, cropImageWidth);
            originalYLineStart += width;
            targetYIndex += cropImageWidth;
            if ((i & 1) == 0) {
                System.arraycopy(yuv420sp, originalUVLineStart + left, cropYuv420sp, targetUVIndex, cropImageWidth);
                originalUVLineStart += width;
                targetUVIndex += cropImageWidth;
            }
        }
        return cropYuv420sp;
    }

2. 裁剪BGR24

public static byte[] cropBgr24(byte[] bgr24, int width, int height, int left, int top, int right, int bottom) {
        if (bgr24 == null || bgr24.length == 0 || width * height * 3 != bgr24.length) {
            throw new IllegalArgumentException("invalid image params!");
        }
        if (left < 0 || top < 0 || right > width || bottom > height) {
            throw new IllegalArgumentException("rect out of bounds!");
        }
        if (right < left || bottom < top) {
            throw new IllegalArgumentException("invalid rect!");
        }
        int cropImageWidth = right - left;
        int cropImageHeight = bottom - top;
        byte[] cropBgr24 = new byte[cropImageWidth * cropImageHeight * 3];

        int originalLineStart = top * width * 3;
        int targetIndex = 0;
        for (int i = top; i < bottom; i++) {
            System.arraycopy(bgr24, originalLineStart + left * 3, cropBgr24, targetIndex, cropImageWidth * 3);
            originalLineStart += width * 3;
            targetIndex += cropImageWidth * 3;
        }
        return cropBgr24;
    }

图像格式转化在人脸识别应用中的实践

一、相关图像颜色空间介绍

1. RGB颜色空间

2. YUV颜色空间

二、相关图像格式介绍

1. BGR24图像格式

2. NV21图像格式

3. NV12图像格式

4. I420图像格式

5. YV12图像格式

6. YUYV图像格式

三、图像格式转换

1. 从Bitmap中获取ARGB_8888图像格式数据(Android平台)

2. ARGB_8888转换为BGR_24

3. ARGB_8888转换为NV21

4. NV21转换为BGR24

5. NV12和NV21的互换

6. NV21转YV12

7. YUYV转NV12

8. I420和YV12的互换

9. I420转换为YUYV

四、图像裁剪

1. 裁剪NV21

9. I420转换为YUYV

四、图像裁剪

1. 裁剪NV21或NV12

2. 裁剪BGR24

1. 从`Bitmap`中获取`ARGB_8888`图像格式数据(Android平台)

2. `ARGB_8888`转换为`BGR_24`

3. `ARGB_8888`转换为`NV21`

4. `NV21`转换为`BGR24`

5. `NV12`和`NV21`的互换

6. `NV21`转`YV12`

7. `YUYV`转`NV12`

8. `I420`和`YV12`的互换

9. `I420`转换为`YUYV`

9. `I420`转换为`YUYV`