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

[Corbin Simpson]

Amos Tibaldi wrote:
> 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?

Which driver, exactly? Most drivers provide RGB Xv formats, and those
that don't probably could be hacked to add it.

~ C.