TV backlight compensation (2020)

Here is an up to date fork with some example shaders: https://github.com/Hello1024/gse-shader

I use it to make sure a 'sensitive' pixel on my screen never turns on (it's a row of pixels which, if the difference between it and the pixels to the side have more than a certain difference in brightness, the whole screen fails - presumably due to a power supply fault in the column driver circuitry).

Love the hacker mindset. Once the problem is solved, the underlying issue loses its appeal :)

Glad I caught this post, I hope the solution can contribute to my problem (although I do not have a way to obtain a fixed ground truth — lighting will change for each picture.)

This exact idea has been floating around in my head for ages, and I always wondered how well it actually worked - now I don't need to wonder. I started thinking about it as a potential solution to OLED burn-in. Thankfully, my OLED TV doesn't have any burn-in yet, so I never needed to investigate further.

I didn't know there was a version of MPC with a live shader editor, that is also very cool. This is actually a pretty good use case for such a feature.

Just looking at the pictures, this does not look like a backlight problem but rather degradation of the liquid crystal layer. Yes, sure, there's interaction between the two. The purple shift, however, is very much something that was happening twenty years ago with some liquid crystal chemistries. Back then you could definitely tell which panels were not using high quality LC fluid.

Apple had this issue with their second generation HD Cinema Display product (the first aluminum enclosure, 24 in, 1920 x 1200 model). Some percentage of them would turn purple. I don't have Apple's stats on this. From my own experience the number fluctuated between 15% to as much of 50% of the panels in a batch going bad after moderate burn-in.

Having said all that, this type of compensation or fix might be OK for a TV at home or the computer monitor on the desk of a doctor or even a coder. Not good --at all-- for someone doing critical color work, such as a graphic artist. The reason is that you introduce spatial nonlinearities and differential errors.

The simplest way to put it is that you no-longer have the full 256 (or 1024) steps per R, G, B channel between 0 and 100%. Hypothetically, you might have 256 for green and, say, 200 for red and 175 for blue. This means that the path from black to white is no longer monotonic. You can have serious color rendering errors through the color space. For example, it might be impossible to make an accurate 50% gray because you just don't have the RGB values needed to accomplish that. Worse yet, everything between 47% and 53% gray might look exactly the same.

You can also introduce serious gamma distortion. If, on top of that, you add a temporal element (video), well, it can be a real mess.

The real solution (for critical workflows) is to replace the panel.

BTW, this can apply to RGB OLED as well.

I was meaning to do something similar to the author[0], but couldn't make time and just used this opportunity to buy an external screen.

I'm glad someone put in the work so that now I may be able to use my original screen again.

[0] My most desperate idea was to run a RDP session locally and process the displayed image. Seemed simpler than trying to modify the content of the screen directly.

I wonder, when applying a linear transformation like in the shader described, will the total available color space decrease? Simply put, if a one-dimensional color value on the arbitrary scale between 1 and 100 needs to be decreased by 20 for correction, the resulting maximum will be 80. Does that mean the total available color values will be less?

Would it be possible to create an inverted image that would correct the backlight by burning in the bright areas? It would seem like a more difficult task to accomplish because pixel burn-in time is a variable that’s hard to measure.

How easy would be to place a cheap LCD at the back of the main screen and mirror the same output (in horizontally inverted mode)?

Technically it might require synchronizing the frame latency differences between the two devices, but would such a hack improve the perceived quality?

The constant ramping of brightness is rather distracting.

But it's a damn shame that you can't throw enough money at manufacturers to make them make monitors without glaring QA problems. No matter how much you spend they sell you shit.