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Solving banding issue with 8770w "DreamColor" screen

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Posted (edited)

After spending significant time and effort to obtain "DC" screen for 8770w (which is essentially a regular IPS panel with fancy board that converts 8bpc LVDS to 10bpc DP), I have finally got and installed one. All works great, except of the one problem...

It has pretty bad banding / posterization in lower shadows. I have tried profiling it in different modes (full range, sRGB, rec709) - issue persists, and it indeed shows only in the lowest part of the characteristic curve. Mids and highlights are represented fine and show low deviation from reference values.

GPU is HP K4000M, Nvidia drivers installed "as it is", video-card is identified without a hitch.

Banding was not present with the original TN panel using the same GPU.


While checking a software side, I have noticed that Win10 has bit depth set to 8-bit...




My initial reaction was, - "Easy, let's change it in `nvidia-settings` and we're all set":


...but that would be too easy, right? After selecting 10bpc and clicking "Apply" screen went off and back on, only to show that depth stayed at 8bpc. Repeating the above few times yielded exactly the same result and I'm not in a hurry to meet a cliched (and laymen) definition of insanity.


Let's check GPU-Z. So far so good, nothing unusual. Notice the highlighted BIOS version and subvendor string: M0RNBhk.png


Time to delve into other tabs. We are running WDDDM v2.4 which supports GPU dithering, but hey... BIOS version has changed! pLZ3jD0.png


Briefly back to `nvidia-settings` to check what is reported by vendor's own utility:



So far, we have two strings for BIOS version:

  1. 80.04.5A.00.02 (let's call it an "A")
  2. (let's call it a "B")


Notice how 2nd one seems to not follow hexademical notation. Lastly, "NVIDIA BIOS" drop-down, reports "A" version: 8eGIP0c.png


...and monitor section which confirms that rig is indeed capable of 10bpc, but currently running at mere 8bpc:



Windows "Adapter settings", reports version "B". It's 2019, diversity is a must.



"NVidia inspector" is of the same opinion:



Now, let's use some seriously legit tools and check-in exported BIOS file in `nvflash`:



Here we have two three interesting findings:

  1. Reported vendor is Dell, not an HP. See this link for details.
  2. BIOS version is back to "A". Have I already mentioned diversity?
  3. MXM module uses MX25L2005 flash storage in WSON-8 packaging. If things go real nasty, we should be able to rescue a patient via Pomona clip and external programmer.


Loading the same file in "Kepler BIOS tweaker" confirms the facts:



EDID settings, courtesy of NVidia Control Panel. Hex dump can be found at the bottom of this post. ZnpmdDk.png

...Shall I be worried about "60.02Hz" refresh rate?


To summarize:

  1. Why two different BIOS versions are reported? Anything to do with UEFI (e.g. HP is sideloading its own during boot)?..
  2. Why two different vendors reported? As far as I remember, this is branded HP GPU.
  3. Where to get "clean" BIOS of K4000M for future experiments? Ideally from 8770w equipped with "DreamColor" panel from a factory.


Link to the dumps, BIOS ROM and monitor EDID: https://mega.nz/#F!zGgRmQIL!9q2QFZtHuK2RQ-WHXMA4Mg (also attached to this post)


Edited by ounces
formatting and files

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Posted (edited)

Fun ensues. As suggested on other forum, I have tried to install v388.16 which has failed  on Windows 10:

Afterwards, I have decided to explore options of updating BIOS.
Here is the latest build I have found: ftp://ftp.hp.com/pub/softpaq/sp62501-63000/sp62640.html

Extracted .ROM from the installation package:

Installing with the latest version of `nvflash`:

Then, I have installed NVidia driver v411.63 (oldest one available in "Archive" section).
Now, it reports HP as vendor, however "persistent 8bpc" bug stayed exactly as before.


While I can switch to 10bpc in NVidia Control Panel, display briefly blinks and returns to 8bpc.

BIOS version reporting is still confusing. This is after re-flashing:

Edited by ounces

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Posted (edited)

Ok, this deserves a new post, I was able to obtain 10bpc output. Here is what was done:

  1. Install HP display assistant --> reset to factory settings --> set colourspace to "native/user"
  2. Reboot in "Safe Mode", use DDU to remove previous NVidia drivers.
  3. Download and install ancient v385.67 directly from HP(sp82364.exe)
  4. Voila!


While banding is much less visible now, I can still see it on 16b gradient. Meh. Questions:

  1. How to update drivers while preserving 10bpc capability?
  2. Could people with DC panel please download the gradient and check if they see any banding at all?


For the record, here is my data from "Display Assistant":

Abovementioned .PNG: https://i.imgur.com/v9W9ou7.png (also, attached to this post)

Photo of my screen (not like it's overly representative...)




Edited by ounces

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