wrong colors with Xv extension and image format id: 0x59565955 (UYVY) from an rgb mapping

[Amos Tibaldi]

Hello,
  I am trying to use the Xv extension in order to display images on windows.
I have obtained the image formats with
 xvc.fo = XvListImageFormats( xvc.display, xvc.port, (int *)&formats );
and I have chosen the format
      id: 0x59565955 (UYVY)
        guid: 55595659-0000-0010-8000-00aa00389b71
        bits per pixel: 16
        number of planes: 1
        type: YUV (packed)

I'd like to convert from RGB to UYVY and I have found that for the struct

typedef struct {
  int id;                      /* Unique descriptor for the format */
  int type;                    /* XvRGB, XvYUV */
  int byte_order;              /* LSBFirst, MSBFirst */
  char guid[16];               /* Globally Unique IDentifier */
  int bits_per_pixel;
  int format;                  /* XvPacked, XvPlanar */
  int num_planes;

  /* for RGB formats only */
  int depth;
  unsigned int red_mask;
  unsigned int green_mask;
  unsigned int blue_mask;

  /* for YUV formats only */
  unsigned int y_sample_bits;
  unsigned int u_sample_bits;
  unsigned int v_sample_bits;
  unsigned int horz_y_period;
  unsigned int horz_u_period;
  unsigned int horz_v_period;
  unsigned int vert_y_period;
  unsigned int vert_u_period;
  unsigned int vert_v_period;
  char component_order[32];    /* eg. UYVY */
  int scanline_order;          /* XvTopToBottom, XvBottomToTop */
} XvImageFormatValues;

that image format has: ysb 8; usb 8; vsb 8; hyp 1; hup 2; hvp 2; vyp 1; vup
1; vvp 1; 'UYVY'slo: 0

So I'm trying to convert the bytes from rgb with:


void RGBToUYVY(unsigned short int r,
               unsigned short int g,
               unsigned short int b,
               unsigned short int * u,
               unsigned short int * y,
               unsigned short int * v)
{
    //cout << "r=" << r << " g=" << g << " b=" << b;
    r &= 0x00FF; g &= 0x00FF; b &= 0x00FF;
   *y = (unsigned short
int)(0.299f*(float)r+0.587f*(float)g+0.114f*(float)b);
    *u = (unsigned short
int)(-0.147f*(float)r-0.289f*(float)g+0.436f*(float)b);
    *v = (unsigned short
int)(0.615f*(float)r-0.515f*(float)g-0.100f*(float)b);
    *y &= 0x00FF;
    *u &= 0x00FF;
    *v &= 0x00FF;
    //cout << " y=" << *y << " u=" << *u << " v=" << *v <<endl;
}

and to display the image with
void XVWindow::Redraw()
{
    unsigned short int u, y, v;
    RGBToUYVY(255,255,0,&u,&y,&v);
    unsigned short int thecolor =  u << 12 | y << 8 | v << 4 | y;

      for ( int y=0; y<ImageHeight; y++ )
    for ( int x=0; x<ImageWidth; x++ )
      ((unsigned short int *)BGimage->data)[ y * ImageWidth + x ] =
thecolor;

    counter++;
            XvPutImage( xvc.display, xvc.port, window, gc,
                    BGimage, 0, 0, ImageWidth, ImageHeight,
                       0, 0, WindowWidth, WindowHeight );
}

but the colors are always different. I have tried to use the blue, the red
and the green to see if I could obtain them separately but the mapping was
always wrong and different colours were showing on the window with respect
to those that I'd like to use in RGB.

What can I do? Is my RGB to UYVY correct? Why do I obtain on the screen
different colours. There are some kind of manual on how to map colors with
XV images?

Thanks in advance,

Amos Tibaldi
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