android – YUV_420_888解读三星Galaxy S7(Camera2)

我写了一个从YUV_420_888到Bitmap的转换,考虑到以下逻辑(据我所知)：

总结该方法：内核的坐标x和y与Y平面(2d分配)的非填充部分的x和y以及输出位图的x和y都是一致的.然而,U平面和V平面具有与Y平面不同的结构,因为它们使用1个字节覆盖4个像素,此外,可能具有多于一个的PixelStride,此外它们可能也有一个可以与Y平面不同的填充.因此,为了通过内核有效地访问U和V,我将它们放入1-d分配并创建索引“uvIndex”,给出相应的U-和V在该1-d分配中的位置,给定( x,y)坐标(非填充)Y平面(以及输出位图).

为了保持rs-Kernel的精简,我通过LaunchOptions限制x范围来排除yPlane中的填充区域(这反映了y平面的RowStride,因此可以在内核中忽略).所以我们只需要考虑uvIndex中的uvPixelStride和uvRowStride,即用于访问u值和v值的索引.

这是我的代码：

Renderscript内核,名为yuv420888.rs

  #pragma version(1)
  #pragma rs java_package_name(com.xxxyyy.testcamera2);
  #pragma rs_fp_relaxed

  int32_t width;
  int32_t height;

  uint picWidth, uvPixelStride, uvRowStride ;
  rs_allocation ypsIn,uIn,vIn;

 // The LaunchOptions ensure that the Kernel does not enter the padding  zone of Y, so yRowStride can be ignored WITHIN the Kernel.
 uchar4 __attribute__((kernel)) doConvert(uint32_t x, uint32_t y) {

 // index for accessing the uIn's and vIn's
uint uvIndex=  uvPixelStride * (x/2) + uvRowStride*(y/2);

// get the y,u,v values
uchar yps= rsGetElementAt_uchar(ypsIn, x, y);
uchar u= rsGetElementAt_uchar(uIn, uvIndex);
uchar v= rsGetElementAt_uchar(vIn, uvIndex);

// calc argb
int4 argb;
    argb.r = yps + v * 1436 / 1024 - 179;
    argb.g =  yps -u * 46549 / 131072 + 44 -v * 93604 / 131072 + 91;
    argb.b = yps +u * 1814 / 1024 - 227;
    argb.a = 255;

uchar4 out = convert_uchar4(clamp(argb, 0, 255));
return out;
}

Java方面：

    private Bitmap YUV_420_888_toRGB(Image image, int width, int height){
    // Get the three image planes
    Image.Plane[] planes = image.getPlanes();
    ByteBuffer buffer = planes[0].getBuffer();
    byte[] y = new byte[buffer.remaining()];
    buffer.get(y);

    buffer = planes[1].getBuffer();
    byte[] u = new byte[buffer.remaining()];
    buffer.get(u);

    buffer = planes[2].getBuffer();
    byte[] v = new byte[buffer.remaining()];
    buffer.get(v);

    // get the relevant RowStrides and PixelStrides
    // (we know from documentation that PixelStride is 1 for y)
    int yRowStride= planes[0].getRowStride();
    int uvRowStride= planes[1].getRowStride();  // we know from   documentation that RowStride is the same for u and v.
    int uvPixelStride= planes[1].getPixelStride();  // we know from   documentation that PixelStride is the same for u and v.


    // rs creation just for demo. Create rs just once in onCreate and use it again.
    RenderScript rs = RenderScript.create(this);
    //RenderScript rs = MainActivity.rs;
    ScriptC_yuv420888 mYuv420=new ScriptC_yuv420888 (rs);

    // Y,U,V are defined as global allocations, the out-Allocation is the Bitmap.
    // Note also that uAlloc and vAlloc are 1-dimensional while yAlloc is 2-dimensional.
    Type.Builder typeUcharY = new Type.Builder(rs, Element.U8(rs));
    typeUcharY.setX(yRowStride).setY(height);
    Allocation yAlloc = Allocation.createTyped(rs, typeUcharY.create());
    yAlloc.copyFrom(y);
    mYuv420.set_ypsIn(yAlloc);

    Type.Builder typeUcharUV = new Type.Builder(rs, Element.U8(rs));
    // note that the size of the u's and v's are as follows:
    //      (  (width/2)*PixelStride + padding  ) * (height/2)
    // =    (RowStride                          ) * (height/2)
    // but I noted that on the S7 it is 1 less...
    typeUcharUV.setX(u.length);
    Allocation uAlloc = Allocation.createTyped(rs, typeUcharUV.create());
    uAlloc.copyFrom(u);
    mYuv420.set_uIn(uAlloc);

    Allocation vAlloc = Allocation.createTyped(rs, typeUcharUV.create());
    vAlloc.copyFrom(v);
    mYuv420.set_vIn(vAlloc);

    // handover parameters
    mYuv420.set_picWidth(width);
    mYuv420.set_uvRowStride (uvRowStride);
    mYuv420.set_uvPixelStride (uvPixelStride);

    Bitmap outBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    Allocation outAlloc = Allocation.createFromBitmap(rs, outBitmap, Allocation.MipmapControl.MIPMAP_NONE, Allocation.USAGE_SCRIPT);

    Script.LaunchOptions lo = new Script.LaunchOptions();
    lo.setX(0, width);  // by this we ignore the y’s padding zone, i.e. the right side of x between width and yRowStride
    lo.setY(0, height);

    mYuv420.forEach_doConvert(outAlloc,lo);
    outAlloc.copyTo(outBitmap);

    return outBitmap;
}

在Nexus 7(API 22)上进行测试,这将返回漂亮的彩色位图.然而,该器件具有平凡的像素值(= 1)并且没有填充(即,行距=宽度).在全新三星S7(API 23)上进行测试我得到颜色不正确的图片 – 除了绿色图片.但是图片并没有表现出对绿色的普遍偏见,只是看起来非绿色不能正确再现.注意,S7应用的u / v像素值为2,没有填充.

由于最关键的代码行是在rs代码中u / v平面的访问uint uvIndex =(…)我认为,可能存在问题,可能是在这里错误地考虑了像素.有人看到解决方案吗？谢谢.

更新：我检查了一切,我很确定关于y,u,v访问的代码是正确的.所以问题必须是u和v值本身.非绿色具有紫色倾斜,并且看到u,v值它们似乎处于约110-150的相当窄的范围内.是否真的有可能需要应对特定设备的YUV – > RBG转换……？！我错过了什么吗？

更新2：已经更正了代码,现在可以使用,感谢Eddy的反馈.

解决方法:

看着

floor((float) uvPixelStride*(x)/2)

它从Y x坐标计算你的U,V行偏移量(uv_row_offset).

如果uvPixelStride = 2,那么当x增加时：

x = 0, uv_row_offset = 0
x = 1, uv_row_offset = 1
x = 2, uv_row_offset = 2
x = 3, uv_row_offset = 3

这是不正确的.由于uvPixelStride = 2,因此uv_row_offset = 1或3时没有有效的U / V像素值.

你要

uvPixelStride * floor(x/2)

(假设你不相信自己要记住整数除法的关键向下舍入行为,如果你这样做的话)：

uvPixelStride * (x/2)

应该够了

有了它,您的映射变为：

x = 0, uv_row_offset = 0
x = 1, uv_row_offset = 0
x = 2, uv_row_offset = 2
x = 3, uv_row_offset = 2

看看是否修复了颜色错误.在实践中,这里的错误寻址将意味着每个其他颜色样本将来自错误的颜色平面,因为底层YUV数据可能是半平面的(因此U平面从V平面1字节开始,两个平面交错)

标签：android-camera2,yuv,android
来源： https://codeday.me/bug/20190918/1810629.html