DC Dimming IPS / Software brightness control

AlanSmith

Found a problem, all new (true 8bit) monitors have "software" brightness control through screen dimming (pixel flickering/dithering at 15Hz). When the brightness decreases, a "filter" is applied (the backlight brightness is always 100%). On all monitors from Redmi/Xiaomi, this is called DC Dimming. The backlight does not flicker on them/but the pixels flicker. Hardware brightness control does not work.

Take for example (8bit)

1) Redmi G24 VA 165Hz

2) Redmi G27 IPS 165Hz

3) Redmi G27Q IPS 2K 165Hz

4) Redmi Q27Q IPS 2025 180Hz

jordan

AlanSmith yup this is why I can't tolerate this fake DC dimming. Oppo also uses this method.

JTL

AlanSmith Found a problem, all new (true 8bit) monitors have "software" brightness control through screen dimming (pixel flickering/dithering at 15Hz).

If it really is 15Hz pixel modulations I wonder if a sensitive enough photodiode and oscilloscope could pick it up.

AlanSmith

It's just cheating buyers. Manufacturers do not write about the presence of dithering (pixel flickering). Even in the specifications (except for the word DC Dimming) there is nothing. How can a person understand that DC Dimming (an analogue of Flicker Free) can mean the exact opposite?

Even "true 8bit" VA monitors flicker. Before us is 8bit = (8bit + FRC) "red eye mode". You no longer need to buy professional monitors (to ruin your eyesight). Now you can do it for just $100. I suspect that IPS phones may have the same problem.

jordan

AlanSmith right its maddening! They are only taking advantage of us getting us to buy it. So they get rid of backlight flicker for pixel flickering at a LOW frequency.. it's absurd. Pixel flicker absolutely wrecks my head. Pwm is more tolerable.

PacificHike

AlanSmith

Hi, I went through your list of monitors on another thread from Feb 2024, but then saw this more recent post of yours. So are there NO true 8 bit monitors that do NOT have this pixel flickering issue?

AgentX20

This doesn't sound like DC dimming as I know it…

We all know that PWM switches the backlight on and off to control brightness. I always thought that DC dimming did something similar in that it lowered the backlight brightness, but did it in a way that didn't flicker using the current to control the brightness directly.

Reading up now, I now understand that DC dimming actually reduces current to the pixels therefore reducing their brightness. The whole point of this DC control is that it doesn't have to flicker to reduce the brightness. The downside is that at low brightness levels on OLEDs you get colour shifts. And I'm left wondering - what they heck then are they doing with the backlight? Is it full power all the time with DC dimmed devices?

So why is it stated here that DC Dimming == flickering pixels?

Or is this some new or different technique with the same name and what's labelled by @jordan as "fake DC Dimming"? If so, it reads like some frankenstein combination of both worlds. Is this just cheap DC dimming in that they're using PWM techniques on the pixels, rather than the backlight??!

JTL

AgentX20 Or is this some new or different technique with the same name and what's labelled by @jordan as "fake DC Dimming"? If so, it reads like some frankenstein combination of both worlds. Is this just cheap DC dimming in that they're using PWM techniques on the pixels, rather than the backlight??!

That's how this alleged issue reads to me.

Really curious if a sensitive enough oscilloscope and diode would pick it up.

PacificHike

(Deleted)

PacificHike

I contacted ViewSonic about their true 10 bit VP2786. I copied and pasted the explanation about the pixel flicker from this post. And ask them about it. This was their response. But maybe they might be wrong (coming from support staff) or not even realize their is pixel flicker because it's from some third-party board inside the monitor? They did take several days to investigate and get back to me. So I'm not sure who they spoke with internally.

*Thank you for your patience. Please see below in regards to "Pixel Flicker".

The VP2786-4K features hardware-based brightness control, adjusting the backlight without relying on pixel-level dithering or low-frequency dimming techniques. Additionally, the panel is a true 10-bit display, further eliminating the need for such methods.*

Sincerely,

ViewSonic^® Sales Support

jordan

PacificHike I've spoken to ViewSonic about that model and these were the responses.

"Thank you for your patience, the VP2786-4K is a DC dimming design."

"Hello Jordan,

I did some further looking, I found information I can share without the NDA, unfortunately it looks like this model does use a FRC.

Color Depth 1.07 Billion colors, 10 Bit with A-FRC"

PacificHike

jordan really? Ah man It even says "True 10 bit". What agent/department gave you that response? I want to send it to the guy that gave me my response.

Mine came from Ishtekharul in Sales Support

jordan

PacificHike Matthew from sales department. Yup false advertisement. Uperfect had a monitor listed as the same and after I called them out they fixed the spec page.

PacificHike

jordan

I shared the other agents response and here is my agent's response:

"*When it was stated that it does not use 'low frequency dimming techniques,' this was referring to the monitor not using PWM for backlight control. Instead, it uses DC dimming for this purpose.

Regarding the color depth, the monitor is indeed a true 10-bit monitor.*

*It’s possible the other agent (Matt) was misinformed at the time.

The information I shared with you has been verified by our engineering team.*

Sincerely,
Ishtekharul
ViewSonic® Sales Support"*

So I don't know if there really is FRC or not, but Perhaps the FRC doesn't matter & it's disabled as long as you set your display to 10-bit? Idk I didn't even know there would be FRC above 10 bits I thought it would be either 6-bit plus FRC or 8-bit plus FRC.

Intel though says if you have a 10-bit monitor and you set the graphics card to 10 bit, the CPU graphics won't use frc. On intels side that is. Heck maybe I'll just order it and see if it works anyways for me and if not I'm going to return it regardless.

technicalitch

how to see this issue and test my monitor?

jordan

PacificHike if you can I would try to ask for the panel model number. If you buy the monitor you may be able to check the panel model in the service menu as well.

PacificHike

jordan I tried asking, sales said "We cannot share information outside of what is stated on the part's description for the panel. Feel free to give it a look below. https://www.viewsonic.com/parts/e-00014495.html"

This was the panel number listed on the link he gave me is this what you're talking about?

Panel, LCD 27" LM270WR5-SSE1 LGD

I also found an owner of the monitor on a forum and asked him to check the menu settings, he said there was nothing regarding the panel number. So it seems like someone would have to take apart the monitor to find out if that number above is not it

jordan

PacificHike oh yes that's it. I looked and it seems to be 10bit according to panel look. It normally would say 8+2frc but it says 10 bit under the spec description. Hopefully it's correct but sure seems to be 10/1.07b colors

The person that checked in the menu, they would need to enter service menu with a certain button combination

PacificHike

jordan

Oh ok, so does mean you think there is no A-FRC then as that agent told you? He was mistaken?

The monitor owner I think did use service menu, not sure but here is what he said "Is the Service Menu the Information menu? If not where's is located?
The OSD Menu > Information shows minimal info like resolution, serial no., etc. no panel model."

jordan

PacificHike If panel look is correct then yes the agent must have given me wrong info. I wonder why they told me that because originally they told me its true 10 bit and then when I asked further they looked into it and said yes 8+2 frc. I looked online but couldnt find the LG datasheet pdf of the panel which should be most accurate.

The service menu is different from the normal OSD menu. Check this - https://forums.blurbusters.com/viewtopic.php?t=8113&start=990 - They show what the service menu looks like. It could be different monitor to monitor but other viewsonic monitors might have a similar service menu button shortcut to this model were talking about.