图像RGB/NV21格式互转

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最近项目需要用到 opencv 和一些图像引擎处理图像，引擎开放的接口都是处理 nv21 格式的数据。从 Bitmap 出来的都是 argb 格式数据，所以使用的话需要互相转化一下。

Pixels to Nv21

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// len(nv21) = len(pixels) * 3 / 2
void pixels_to_nv21(unsigned int *pixels, unsigned char *nv21, int width, int height) {
    int w, h;
    int shift = 14, offset1 = 8192, offset2 = 2105344;
    int C0 = 1868, C1 = 9617, C2 = 4899, C3 = 11682, C4 = 9241;

    int r1, r2, g1, g2, b1, b2;

    unsigned int *pRGB1 = pixels;
    unsigned int *pRGB2 = pixels + width;

    unsigned char *pDY1 = nv21;
    unsigned char *pDY2 = nv21 + width;
    unsigned char *pDUV = nv21 + width * height;

    for (h = 0; h < height; h += 2) {
        for (w = 0; w < width; w += 2) {
            int pixel = *pRGB1++;
            b1 = pixel & 255;
            pixel >>= 8;
            g1 = pixel & 255;
            pixel >>= 8;
            r1 = pixel & 255;
            *pDY1 = (b1 * C0 + g1 * C1 + r1 * C2 + offset1) >> shift;
            *pDUV++ = ((r1 - *pDY1) * C3 + offset2) >> shift;
            *pDUV++ = ((b1 - *pDY1) * C4 + offset2) >> shift;
            pDY1++;

            pixel = *pRGB1++;
            b1 = pixel & 255;
            pixel >>= 8;
            g1 = pixel & 255;
            pixel >>= 8;
            r1 = pixel & 255;
            *pDY1 = (b1 * C0 + g1 * C1 + r1 * C2 + offset1) >> shift;
            pDY1++;

            pixel = *pRGB2++;
            b2 = pixel & 255;
            pixel >>= 8;
            g2 = pixel & 255;
            pixel >>= 8;
            r2 = pixel & 255;
            *pDY2 = (b2 * C0 + g2 * C1 + r2 * C2 + offset1) >> shift;
            pDY2++;

            pixel = *pRGB2++;
            b2 = pixel & 255;
            pixel >>= 8;
            g2 = pixel & 255;
            pixel >>= 8;
            r2 = pixel & 255;
            *pDY2 = (b2 * C0 + g2 * C1 + r2 * C2 + offset1) >> shift;
            pDY2++;
        }
        pRGB1 += width;
        pRGB2 += width;
        pDY1 += width;
        pDY2 += width;
    }
}

Nv21 to Pixels

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void nv21_to_pixels(unsigned char *nv21, unsigned int *pixels, int width, int height) {
    int w, h;
    int shift = 14, offset = 8192;
    int C0 = 22987, C1 = -11698, C2 = -5636, C3 = 29049;

    int y1, y2, u1, v1;

    unsigned char *pY1 = nv21;
    unsigned char *pY2 = nv21 + width;
    unsigned char *pUV = nv21 + width * height;

    unsigned char *pD1 = pixels;
    unsigned char *pD2 = pixels + width;
    int pixel = 0;

    for (h = 0; h < height; h += 2) {
        for (w = 0; w < width; w += 2) {
            pixel = 0;
            v1 = *pUV - 128;
            pUV++;
            u1 = *pUV - 128;
            pUV++;


            y1 = *pY1;
            y2 = *pY2;

            pixel |= CLAP(y1 + ((u1 * C3 + offset) >> shift));
            pixel |= CLAP(y1 + ((u1 * C2 + v1 * C1 + offset) >> shift)) << 8;
            pixel |= CLAP(y1 + ((v1 * C0 + offset) >> shift)) << 16;
            *pD1++ = pixel;
            pixel = 0;
            pixel |= CLAP(y2 + ((u1 * C3 + offset) >> shift));
            pixel |= CLAP(y2 + ((u1 * C2 + v1 * C1 + offset) >> shift)) << 8;
            pixel |= CLAP(y2 + ((v1 * C0 + offset) >> shift)) << 16;
            *pD2++ = pixel;

            pY1++;
            pY2++;
            y1 = *pY1;
            y2 = *pY2;
            pixel = 0;
            pixel |= CLAP(y1 + ((u1 * C3 + offset) >> shift));
            pixel |= CLAP(y1 + ((u1 * C2 + v1 * C1 + offset) >> shift));
            pixel |= CLAP(y1 + ((v1 * C0 + offset) >> shift));
            *pD1++ = pixel;
            pixel = 0;
            pixel |= CLAP(y2 + ((u1 * C3 + offset) >> shift));
            pixel |= CLAP(y2 + ((u1 * C2 + v1 * C1 + offset) >> shift));
            pixel |= CLAP(y2 + ((v1 * C0 + offset) >> shift));
            *pD2++ = pixel;
            pY1++;
            pY2++;

        }
        pY1 += width;
        pY2 += width;
        pD1 += width;
        pD2 += width;
    }
}

Pixels to Nv21(bytes)

需要这个的原因是，项目有个功能需要接的 api 是用的 camera1 接口出来的 yuv420 数据（byte[] frame）。

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byte[] encode_yuv420(int[] argb, int width, int height) {
    int size = (int) ((Math.ceil(width / 2.0)) * (Math.ceil(height / 2.0)));
    int frameSize = width * height;
    byte[] yuvs = new byte[frameSize + size * 2];
    int y = 0, u = 0, v = 0;
    int r = 0, g = 0, b = 0;
    int index = 0, uvindex = frameSize;
    for (int i = 0; i < height; i++) {
        for (int j = 0; j < width; j++) {
            r = (argb[index] >> 16) & 255;
            g = (argb[index] >> 8) & 255;
            b = argb[index] & 255;
            y = (int) (0.299 * r + 0.587 * g + 0.114 * b);
            u = (int) (-0.1687 * r - 0.3313 * g + 0.5 * b + 128);
            v = (int) (0.5 * r - 0.4187 * g - 0.0813 * b + 128);
            yuvs[index++] = (byte) ((y < 0) ? 0 : ((y > 255) ? 255 : y));
            if (((i | j) & 1) == 0) {
                yuvs[uvindex++] = (byte) ((u < 0) ? 0 : ((u > 255) ? 255 : u));
                yuvs[uvindex++] = (byte) ((v < 0) ? 0 : ((v > 255) ? 255 : v));
            }
        }
    }
    return yuvs;
}