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Blur reduction possible on any monitor via software ?

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Re: Blur reduction possible on any monitor via software ?

Postby Curi0 » 09 Nov 2017, 06:37

Chief Blur Buster wrote:No guarantees.

Monitor firmware not designed for strobing may still mess timing up enough to cause it to flicker.

Or it might do things like poll the register only once a refreah cycle, making it impossible to get sub-refresh-cycle persistence.

But give it a try, it would be fun to see how deterministic we can get DDC/CI signalled strobing! If you are determined (pun) to do it.


How should I flash the backlight like how many milliseconds after VSYNC should I turn back on the backlight
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Re: Blur reduction possible on any monitor via software ?

Postby Chief Blur Buster » 09 Nov 2017, 12:14

Curi0 wrote:How should I flash the backlight like how many milliseconds after VSYNC should I turn back on the backlight

Remember VSYNC is part of the blanking interval (called VBI -- Vertical Blanking Interval) which is the time period between the last pixel row of the previous refresh cycle, and the first pixel row of the next refresh cycle. Usually this is only 0.5ms or less for VESA GTF (Generalized Timings Formula) so that's why I recommend Large Vertical Totals instead of using default Custom Resolution settings.

Strobe length:
--> As briefly as possible, you ideally want to flash as short as you can. Between 1ms to 2ms
--> It needs to be short enough to be shorter flash than the time period of a VBI
--> It needs to be long enough not to be too dim
--> Expect a 80-90% dimmer picture since the backlight is off 80-90% of the time.
This is normal for non-boosted strobing. Some monitors use voltage-boosted strobes since you can often flash a LED approximately 3x brighter than steady-state. Monitors not designed for strobing, will not support this.

Strobe phase (flash timing offset)
--> Begin your flash at least half a GtG cycle after the beginning of VBI. Ideal strobe phase varies a lot depending on VBI size, refresh rate, overdrive settings, panel type.
You want a real-time strobe phase adjustment (onscreen slider or application window) so you can adjust while viewing http://www.testufo.com/crosstalk in order to "calibrate" your strobe phase. Earlier flash timing will shift the "crosstalk-band" upwards and later flash timing will shift the "crosstalk-band" downwards. You adjust this until it's vertically symmetric: Center clearest with top/bottom edges equal crosstalk

Make sure you don't forget large blanking intervals!
For a longer strobe flash with less crosstalk, modify your resolution (e.g. ToastyX CRU) so the VBI is longer than your planned strobe flash length.
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Re: Blur reduction possible on any monitor via software ?

Postby Curi0 » 09 Nov 2017, 20:22

Chief Blur Buster wrote:
Curi0 wrote:How should I flash the backlight like how many milliseconds after VSYNC should I turn back on the backlight

Remember VSYNC is part of the blanking interval (called VBI -- Vertical Blanking Interval) which is the time period between the last pixel row of the previous refresh cycle, and the first pixel row of the next refresh cycle. Usually this is only 0.5ms or less for VESA GTF (Generalized Timings Formula) so that's why I recommend Large Vertical Totals instead of using default Custom Resolution settings.

Strobe length:
--> As briefly as possible, you ideally want to flash as short as you can. Between 1ms to 2ms
--> It needs to be short enough to be shorter flash than the time period of a VBI
--> It needs to be long enough not to be too dim
--> Expect a 80-90% dimmer picture since the backlight is off 80-90% of the time.
This is normal for non-boosted strobing. Some monitors use voltage-boosted strobes since you can often flash a LED approximately 3x brighter than steady-state. Monitors not designed for strobing, will not support this.

Strobe phase (flash timing offset)
--> Begin your flash at least half a GtG cycle after the beginning of VBI. Ideal strobe phase varies a lot depending on VBI size, refresh rate, overdrive settings, panel type.
You want a real-time strobe phase adjustment (onscreen slider or application window) so you can adjust while viewing http://www.testufo.com/crosstalk in order to "calibrate" your strobe phase. Earlier flash timing will shift the "crosstalk-band" upwards and later flash timing will shift the "crosstalk-band" downwards. You adjust this until it's vertically symmetric: Center clearest with top/bottom edges equal crosstalk

Make sure you don't forget large blanking intervals!
For a longer strobe flash with less crosstalk, modify your resolution (e.g. ToastyX CRU) so the VBI is longer than your planned strobe flash length.


Instead of using long VBI will sleeping before the strobe flash work ?

Also could something like this work on CCFL monitors
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Re: Blur reduction possible on any monitor via software ?

Postby Chief Blur Buster » 11 Nov 2017, 18:56

Curi0 wrote:Instead of using long VBI will sleeping before the strobe flash work ?

By asking this question, it indicates you may not fully grasp the "law-of-physics" problem.
So I'll attempt to explain diagrammatically soon.

First, view this high speed video of http://www.testufo.com/flicker:

phpBB [video]


This comes from Understanding LCD Refresh Behavior Via High Speed Video.

In short:
--> LCDs are scanned top-to-bottom over the period of a refresh cycle.
--> The blanking interval is like a pause between refresh cycles.
--> Large blanking interval means more time to finish pixel transitions at bottom edge of the screen, before beginning top edge for next refresh cycle.
--> You want to flash the backlight in between refresh cycles.
--> If the time period between refresh cycles is too small (small blanking interval), LCD GtG is not finished at bottom edge when LCD GtG begins at top edge. GtG overlaps refresh cycles. That's bad for strobing. You have more strobe crosstalk overlapping refresh cycles.
Therefore, the height of VBI needs to be taller than the "GtG" zone (the vertical wipe effect) to successfully fit pixel transitions offscreen between refresh cycles.

Sometimes the GtG zone is taller than a refresh cycle (like on an old 33ms 60Hz LCD) then you've essentially instead got streaking (3 refresh cycles overlapping each other) -- this is extremely streaky-looking.

Even today, GtG barely fits in the VBI, but that's the name of the game for a good strobe backlight.
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Re: Blur reduction possible on any monitor via software ?

Postby Curi0 » 12 Nov 2017, 22:01

Chief Blur Buster wrote:
Curi0 wrote:Instead of using long VBI will sleeping before the strobe flash work ?

By asking this question, it indicates you may not fully grasp the "law-of-physics" problem.
So I'll attempt to explain diagrammatically soon.

First, view this high speed video of http://www.testufo.com/flicker:

phpBB [video]


This comes from Understanding LCD Refresh Behavior Via High Speed Video.

In short:
--> LCDs are scanned top-to-bottom over the period of a refresh cycle.
--> The blanking interval is like a pause between refresh cycles.
--> Large blanking interval means more time to finish pixel transitions at bottom edge of the screen, before beginning top edge for next refresh cycle.
--> You want to flash the backlight in between refresh cycles.
--> If the time period between refresh cycles is too small (small blanking interval), LCD GtG is not finished at bottom edge when LCD GtG begins at top edge. GtG overlaps refresh cycles. That's bad for strobing. You have more strobe crosstalk overlapping refresh cycles.
Therefore, the height of VBI needs to be taller than the "GtG" zone (the vertical wipe effect) to successfully fit pixel transitions offscreen between refresh cycles.

Sometimes the GtG zone is taller than a refresh cycle (like on an old 33ms 60Hz LCD) then you've essentially instead got streaking (3 refresh cycles overlapping each other) -- this is extremely streaky-looking.

Even today, GtG barely fits in the VBI, but that's the name of the game for a good strobe backlight.


I'm currently writing a kernel module for this.

I recorded a 120fps video slowed down to x0.125

60hz
phpBB [video]

106hz
phpBB [video]


[Chief Blur Buster's Editor Note: These videos are not possible to correctly interpret without using a higher speed camera, such as 1000fps.]
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Re: Blur reduction possible on any monitor via software ?

Postby Sparky » 12 Nov 2017, 23:03

Kinda hard to tell what's the backlight flashing, and what's the test pattern. Maybe try the moving photo test?
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Re: Blur reduction possible on any monitor via software ?

Postby Curi0 » 13 Nov 2017, 00:07

Sparky wrote:Kinda hard to tell what's the backlight flashing, and what's the test pattern. Maybe try the moving photo test?


In the video the backlight isn't flickering it's just on normally
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Re: Blur reduction possible on any monitor via software ?

Postby Sparky » 13 Nov 2017, 16:34

Curi0 wrote:
Sparky wrote:Kinda hard to tell what's the backlight flashing, and what's the test pattern. Maybe try the moving photo test?


In the video the backlight isn't flickering it's just on normally
Looks like overdrive isn't set high enough. Even in the 60hz video you can see 3 frames in a single exposure.
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Re: Blur reduction possible on any monitor via software ?

Postby Curi0 » 15 Nov 2017, 07:59

Sparky wrote:
Curi0 wrote:
Sparky wrote:Looks like overdrive isn't set high enough. Even in the 60hz video you can see 3 frames in a single exposure.

The LCD has no overdrive option.Is there a timing or setting which I can use to reduce the ghosting.I've hit some limitations of the Linux DRM (cannot execute something on VSYNC in kernel module) but I'm working on it.
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Re: Blur reduction possible on any monitor via software ?

Postby lexlazootin » 15 Nov 2017, 08:29

Not really, you can kinda help it with a fast scanout by raising the vertical total to a higher value but you might need to lower your refreshrate to do that to fit within the pixelclock limit but even if you do a fast scanout with a high vertical total 3 frames of ghosting will still be there.
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