[KSF phosphor] How does Red Frame Insertion work and does it have the potential I think does?
Posted: 24 Jan 2023, 01:03
I have an AOC ultrawide monitor and while I was messing around with the OSD, I noticed there was an option called "MBR" (motion blur reduction) and I decided to turn it on and look at it through a slow-motion camera out of curiosity. I was expecting to see black frames in between the frames or some black flicker. But I was surprised when I saw what appeared to be red frames instead. I've uploaded some slow motion footage on YouTube so you can get an idea of how it looks (the red frames are not visible in real life).
I tried looking up red frame insertion online, but there's hardly any mention of it. I also believe that this monitor isn't fully utilizing red frame insertion as it has a slow VA panel which isn't fast enough to drive the monitor's 144Hz refresh rate without significant overshoot. I've heard that there projectors with red frame insertion, and if they have a fast enough response time, it should be easier to see how RFI (Red Frame Insertion) Compares to BFI (Black Frame Insertion).
I do see some potential upsides of RFI (especially for OLED) and these may or may not be true. I'm speculating based on my observations and knowledge. The first potential upside is the lower brightness penalty. I've noticed that setting the MBR slider all to way to 20 on my monitor doesn't reduce the brightness as much as I expected, unlike other monitors/TV's I've seen with BFI/backlight strobing. This lower brightness penalty makes sense if you understand Talbot Plateau's law. Basically, the increase in motion clarity from strobing is proportional to the decrease in brightness (assuming no bottlenecks in GtG response time). So, if you strobe enough to double motion clarity/cut MPRT by half, the brightness gets also gets cut in half. This makes more sense if you think of it like averages. Imagine you're strobing and half of the time your monitor is displaying completely black frames at 0 nits and the other half of the time your monitor is displaying 400 nits. (400-0)/2= 200, so the brightness you perceive will be 200 nits. The fact that the red frames appear red on camera tells me that its brightness is a non zero number, otherwise they would be black.
It seems like magic that my eyes are unable to perceive these red frames, but I'm sure there's some scientific explanation. My main question would be, why is there a brightness penalty at all? Could we not match the brightness of the inserted red frames with the normal frames? Would the red frames being too bright somehow make it visible to the human eye? If Red Frame insertion could be done without brightness loss, that would be especially huge for OLED as it's not very bright to begin with and black frame insertion kills the brightness even further. I could also see RFI + HDR being implemented together, as the brightness of certain highlights can be matched proportionally on the red frames.
The last potential upside of RFI I see, specifically benefits OLED and self emissive technologies. Basically, OLED's slowest GtG times tend to be when the pixels turn off and on (when colors change to and from black), which is exactly what BFI is doing. I don't think this is an issue with OLED's right now, but it may become a problem as OLED's approach those higher refresh rates. With redframe insertion, the OLED pixel changes it's color to and from red, so the pixel response times when strobing with OLED should always be faster with red frames over black frames. LCD's can turn off their backlight independent of their pixels, so only the laws of physics would limit how fast the backlight could turn on and off. With RFI, the limit at which LCD's could flicker would be limited by it's GtG response times. So possibly excluding brightness, BFI still seems to be superior over RFI on LCD displays.
I tried looking up red frame insertion online, but there's hardly any mention of it. I also believe that this monitor isn't fully utilizing red frame insertion as it has a slow VA panel which isn't fast enough to drive the monitor's 144Hz refresh rate without significant overshoot. I've heard that there projectors with red frame insertion, and if they have a fast enough response time, it should be easier to see how RFI (Red Frame Insertion) Compares to BFI (Black Frame Insertion).
I do see some potential upsides of RFI (especially for OLED) and these may or may not be true. I'm speculating based on my observations and knowledge. The first potential upside is the lower brightness penalty. I've noticed that setting the MBR slider all to way to 20 on my monitor doesn't reduce the brightness as much as I expected, unlike other monitors/TV's I've seen with BFI/backlight strobing. This lower brightness penalty makes sense if you understand Talbot Plateau's law. Basically, the increase in motion clarity from strobing is proportional to the decrease in brightness (assuming no bottlenecks in GtG response time). So, if you strobe enough to double motion clarity/cut MPRT by half, the brightness gets also gets cut in half. This makes more sense if you think of it like averages. Imagine you're strobing and half of the time your monitor is displaying completely black frames at 0 nits and the other half of the time your monitor is displaying 400 nits. (400-0)/2= 200, so the brightness you perceive will be 200 nits. The fact that the red frames appear red on camera tells me that its brightness is a non zero number, otherwise they would be black.
It seems like magic that my eyes are unable to perceive these red frames, but I'm sure there's some scientific explanation. My main question would be, why is there a brightness penalty at all? Could we not match the brightness of the inserted red frames with the normal frames? Would the red frames being too bright somehow make it visible to the human eye? If Red Frame insertion could be done without brightness loss, that would be especially huge for OLED as it's not very bright to begin with and black frame insertion kills the brightness even further. I could also see RFI + HDR being implemented together, as the brightness of certain highlights can be matched proportionally on the red frames.
The last potential upside of RFI I see, specifically benefits OLED and self emissive technologies. Basically, OLED's slowest GtG times tend to be when the pixels turn off and on (when colors change to and from black), which is exactly what BFI is doing. I don't think this is an issue with OLED's right now, but it may become a problem as OLED's approach those higher refresh rates. With redframe insertion, the OLED pixel changes it's color to and from red, so the pixel response times when strobing with OLED should always be faster with red frames over black frames. LCD's can turn off their backlight independent of their pixels, so only the laws of physics would limit how fast the backlight could turn on and off. With RFI, the limit at which LCD's could flicker would be limited by it's GtG response times. So possibly excluding brightness, BFI still seems to be superior over RFI on LCD displays.