I connected QNX 7.1 HDMI output to an Xilinx video capture device and found that the pixel RGB value range is limited to
 [0x10~0xEB] but not [0x00~0xFF]. For example, when I display red (0xFF0000) color on QNX, we got color (0xEB1010) on 
video capture device, and when we display black (0x000000) color, we got color (0x101010). 
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Some pixels value mapping
Pixel on QNX  Pixel on video capture
------------  ----------------------
00            10
01            10
02            11
03            12
04            13
05            14
06            15
07            16
08            16
09            17
0A            18
0B            19
0C            1A
0D            1B
0E            1C

FD            E9
FE            EA
FF            EB

However, when we connected ubuntu/Window10 HDMI output to the same video capture device, everything works fine.
When I used screenshot utility to capture the display on QNX 7.1, we got the correct color(the RGB range is [0x00~0xFF])
.

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The graphics.conf is:

begin khronos

  begin egl display 1
    egl-dlls = libglapi-mesa.so libEGL-mesa.so
    glesv1-dlls = libglapi-mesa.so libGLESv1_CM-mesa.so
    glesv2-dlls = libglapi-mesa.so libGLESv2-mesa.so
    gpu-dlls = gpu_drm.so
  end egl display

  begin wfd device 1
    wfd-dlls = libwfdcfg-intel-generic.so libWFDintel-drm.so

    # Run "drm-probe-displays" to list the available displays and pipelines,
    # and "use $GRAPHICS_ROOT/libWFDintel-drm.so" for more information on
    # these driver-specific settings.

    # Here is displays map for DH370:
    # display 1: DisplayPort (DP-1)
    # display 2: DisplayPort (DP-2)
    # display 3: HDMI-A (HDMI-A-1)
    # display 4: DisplayPort (DP-3), default
    # display 5: HDMI-A (HDMI-A-2)
    # display 6: DisplayPort (DP-4)
    # display 7: HDMI-A (HDMI-A-3)

    # Pipeline IDs 1 to 9 are used for DRM CRTCs.  One should be assigned
    # to each display that will be used.
    pipeline1-display = 1
    pipeline2-display = 2
    pipeline3-display = 4 # this is the display id which identified by drm-probe-display, the only hdmi output on DH370
  end wfd device

end khronos

begin winmgr

  begin globals
    default-display = 4 # the default display id, 4 is the only one hdmi output on DH370
    # Adjust the stack size of Screen's resmgr threads.  The default size
    # is insufficient for blitters/compositors using Mesa (e.g., gles2blt).
    stack-size = 65536  # in units of bytes
    blit-config = inteldrm
    alloc-config = inteldrm
    requests-logsize = 65536
    blits-logsize = 4096
  end globals

  begin display 1
    video-mode = 1920 x 1080 @ 60
    # Adjust the stack size of Screen's composition thread; required when the
    # display's framebuffer uses Mesa (e.g., "usage = gles2"), as noted above.
    stack-size = 65536  # in units of bytes
  end display

  begin display 2
    video-mode = 1920 x 1080 @ 60
    # Adjust the stack size of Screen's composition thread; required when the
    # display's framebuffer uses Mesa (e.g., "usage = gles2"), as noted above.
    stack-size = 65536  # in units of bytes
  end display

  begin display 4
    video-mode = 1920 x 1080 @ 60
    # Adjust the stack size of Screen's composition thread; required when the
    # display's framebuffer uses Mesa (e.g., "usage = gles2"), as noted above.
    stack-size = 65536  # in units of bytes
  end display

  begin class framebuffer-1
    display = 1
    pipeline = 1
    format = rgba8888
    usage = inteldrm
  end class

  begin class framebuffer-2
    display = 2
    pipeline = 2
    format = rgba8888
    usage = inteldrm
  end class

  begin class framebuffer-3
    display = 4
    pipeline = 3
    format = rgba8888
    usage = inteldrm
  end class

end winmgr

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/root# cat...