[Bug 1896186] Re: Raspberry Pi HDMI output looks dull, low contrast

[Dave Jones]

>From the Pi's config.txt docs at
https://www.raspberrypi.org/documentation/configuration/config-
txt/video.md :

  "The hdmi_pixel_encoding command forces the pixel encoding mode. By
default, it will use the mode requested from the EDID, so you shouldn't
need to change it."

Which would suggest that if the wrong encoding is being selected for
your monitor, then it's because your monitor is transmitting the wrong
information in its EDID. However, the table below that states that the
default is "RGB limited for CEA, RGB full for DMT" which suggests (to me
at least) that the heuristic is rather simpler and that any CEA (TV)
mode gets the limited 16-235 range (which is typical for TVs), while any
DMT (monitor) mode gets the full 0-255 range.

It might be useful to query what EDID the Pi is getting from your
monitor. I don't *think* this works when the KMS overlay is loaded, but
if you boot the server image, install "libraspberrypi-bin" on it, then
run "tvservice -d edid.dat" that should dump the EDID the pi's firmware
received from your monitor. If you could attach that we could take a
look at what might be going on?

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https://bugs.launchpad.net/bugs/1896186

Title:
  Raspberry Pi HDMI output looks dull, low contrast

Status in linux-firmware-raspi2 package in Ubuntu:
  Triaged

Bug description:
  HDMI colour looks dull, low contrast on Raspberry Pi.

  Workaround/fix: Edit /boot/firmware/usercfg.txt and add a new line:

    hdmi_pixel_encoding=2

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