android - 将 NV12 yuv 转换为 RGB 的 Renderscript

Question

我在下面编写代码将 NV12 yuv 转换为 RGB，但颜色不正确。yuv2rgb.rs

#pragma version(1)
#pragma rs java_package_name(com.example.myexam)
#pragma rs_fp_relaxed

rs_allocation gYUV;
uint32_t gW;
uint32_t gH;

uchar4 __attribute__((kernel)) YUV2RGB(uint32_t x,uint32_t y)
{
    uchar yps = rsGetElementAt_uchar(gYUV, x, y);
    uchar u = rsGetElementAt_uchar(gYUV,(x & ~1),gH + (y>>1));
    uchar v = rsGetElementAt_uchar(gYUV,(x & ~1)+1,gH + (y>>1));
    uchar4 rgb = rsYuvToRGBA_uchar4(yps, u, v);
    return rgb;
}

java代码:

public Bitmap NV12_toRGB(byte[] yuv,int W,int H) {
    RenderScript rs = RenderScript.create(this);
    Type.Builder yuvBlder = new Type.Builder(rs, Element.U8(rs))
            .setX(W).setY(H*3/2);
    Allocation allocIn = Allocation.createTyped(rs,yuvBlder.create(),Allocation.USAGE_SCRIPT);
    Type rgbType = Type.createXY(rs, Element.RGBA_8888(rs), W, H);
    Allocation allocOut = Allocation.createTyped(rs,rgbType,Allocation.USAGE_SCRIPT);

    ScriptC_yuv2rgb scriptC_yuv2rgb = new ScriptC_yuv2rgb(rs);
    scriptC_yuv2rgb.set_gW(W);
    scriptC_yuv2rgb.set_gH(H);
    allocIn.copyFrom(yuv);
    scriptC_yuv2rgb.set_gYUV(allocIn);
    scriptC_yuv2rgb.forEach_YUV2RGB(allocOut);

    Bitmap bmp = Bitmap.createBitmap(W, H, Bitmap.Config.ARGB_8888);
    allocOut.copyTo(bmp);

    allocIn.destroy();
    scriptC_yuv2rgb.destroy();
    return bmp;
}

我猜 (x,y) 是矩阵坐标，所以 y 应该在 (x,y)，u 应该在 ((x/2)*2,H + y/2)，v 应该是在你旁边，((x/2)*2+1,H + y/2)。听起来这个逻辑是错误的!

Answer 1

需要修复两个错误:

1. -1 应该是 ~1，因为 x & -1 刚好等于 x，但 x & ~1 会屏蔽掉最后一位，因此保持值均匀。
2. yuv 矩阵大小不正确。由于 uv 向量存储在 y 数据的末尾，因此总矩阵大小应为 W*H*3/2。

应用这两个更改后，它工作正常。java:

public Bitmap YUV_toRGB(byte[] yuv,int W,int H) {
        RenderScript rs = RenderScript.create(this);
        Type.Builder yuvBlder = new Type.Builder(rs, Element.U8(rs))
                .setX(W).setY(H*3/2);
        Allocation allocIn = Allocation.createTyped(rs,yuvBlder.create(),Allocation.USAGE_SCRIPT);
        Type rgbType = Type.createXY(rs, Element.RGBA_8888(rs), W, H);
        Allocation allocOut = Allocation.createTyped(rs,rgbType,Allocation.USAGE_SCRIPT);

        ScriptC_yuv2rgb scriptC_yuv2rgb = new ScriptC_yuv2rgb(rs);
        allocIn.copyFrom(yuv);
        scriptC_yuv2rgb.set_gW(W);
        scriptC_yuv2rgb.set_gH(H);
        scriptC_yuv2rgb.set_gYUV(allocIn);
        scriptC_yuv2rgb.forEach_YUV2RGB(allocOut);

        Bitmap bmp = Bitmap.createBitmap(W, H, Bitmap.Config.ARGB_8888);
        allocOut.copyTo(bmp);

        allocIn.destroy();
        scriptC_yuv2rgb.destroy();
        return bmp;
    }

yuv2rgb.rs

#pragma version(1)
#pragma rs java_package_name(com.example.myexam)
#pragma rs_fp_relaxed

rs_allocation gYUV;
uint32_t gW;
uint32_t gH;

uchar4 __attribute__((kernel)) YUV2RGB(uint32_t x,uint32_t y)
{
    uchar yps = rsGetElementAt_uchar(gYUV, x, y);
    uchar u = rsGetElementAt_uchar(gYUV,(x & ~1),gH + (y>>1));
    uchar v = rsGetElementAt_uchar(gYUV,(x & ~1)+1,gH + (y>>1));
    uchar4 rgb = rsYuvToRGBA_uchar4(yps, u, v);
    return rgb;
}