How to show a pic for exactly 12.5ms? [tachitoscope]

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ShadowIllusion
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Joined: 23 Feb 2014, 14:51

How to show a pic for exactly 12.5ms? [tachitoscope]

Post by ShadowIllusion » 23 Feb 2014, 15:11

I want to present a pic(human face) last only for 12.5ms or even shorter time period. But after read some of the articles that posted here, I've got really lost.
Could anyone help me on this problem, what should I do to show a pic on screen for exactly 12.5ms(and disappears)? Or what should I have/buy?
Does 120HZ or 144HZ monitor only matters? Or I should also consider on other special technology such as use black frame to remove the persistence?

[Editor's Note: What you're looking for is a "tachitoscope"]

HeLLoWorld
Posts: 33
Joined: 07 Jan 2014, 18:44

Re: How to show a pic for exactly 12.5ms?

Post by HeLLoWorld » 23 Feb 2014, 23:39

Seems like research on subliminal images.
Right now the best solution I think of is a gsync display with a custom written program, if the timing has to be exact. That should give you 7 to 33ms in about 1ms steps then 40 to maybe 66 etc. Maybe I might write it. However gsync is out of stock right now. Or consider modding a led monitor send a variable pulse of light if you just want black before and after.
If you need insertion into a stream and standard display a 144Hz monitor will give you multiples of 7ms and 120Hz multiples of 8. Lightboost could give you between 1.4 and 2.4 but that's it. Maybe a slide projector, an hl led flashlight and an arduino is all you want and maybe a smartphone flash could do it.

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Chief Blur Buster
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Re: How to show a pic for exactly 12.5ms?

Post by Chief Blur Buster » 23 Feb 2014, 23:52

ShadowIllusion wrote:I want to present a pic(human face) last only for 12.5ms or even shorter time period. But after read some of the articles that posted here, I've got really lost.
What you are probably looking for is a tachitoscope.
http://en.wikipedia.org/wiki/Tachistoscope

You can do a hardware-based modification of a computer monitor (e.g. LightBoost) to flash the backlight for a specific time duration, to accomplish this. StrobeMaster has written about this at Display Corner: http://display-corner.epfl.ch/index.php/Main_Page
See the left sidebar.

Another option of trying to pull off 12.5ms with an existing monitor would require an exactly (1000ms/12.5ms = 80 refresh cycles per second) (12.5ms = 1/80sec) which means you need 80Hz sample-and-hold display (e.g. LCD) with a fast pixel response (preferably 1ms or less). Some LCD displays, including GSYNC, can clock to exactly 80Hz, which would give you frametimes of 12.5ms, but if you get a non-GSYNC display, make sure you do the TestUFO Frame Skipping Test at http://www.testufo.com/frameskipping ... and be aware that GtG pixel transitions can fuzzy up the 12.5ms period with a significant error margin. You'll want a TN LCD, for the fastest GtG, and you'll want one that is multisync so you can configure a custom refresh rate that matches the refresh cycle duration you are targetting. Some colors will transition fast and some colors will transition slow, so you may end up with 12.5ms +/- 2ms error, if you try to do a refresh-controlled method. Refresh controlled methods can include GSYNC, which is capable of any arbitrary refresh rate in very tiny increments (sub-millisecond increments). If some error margin is acceptable, there are a few TN LCDs that are multisync and would be suitable for this. However, if you need ultra precision, you instead want to use a monitor that can be hacked to flash the backlight for a custom duration of your choice.

Modifying a LCD monitor into a tachitoscope (making backlight to flash for a specific duration) is a lot more guaranteed way of doing things, to get 12.5ms frame times.

Since this is a scientific topic, I'm moving this thread to Area51.
Feel free to ask further questions.
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spacediver
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Re: How to show a pic for exactly 12.5ms? [tachitoscope]

Post by spacediver » 25 Feb 2014, 04:07

great response. For my own research, I'd love to have a strobed backlight (as opposed to a scanning backlight), as I'm measuring responses to faces that are presented for very brief intervals, and am particularly interested in the onset and offset transients associated with the onset and offset of the stimuli. As it stands, it takes a whole frame for the image to disappear, and while this probably doesn't affects things significantly, it would be nice to have the option of a tachistoscopic presentation.

ShadowIllusion
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Re: How to show a pic for exactly 12.5ms? [tachitoscope]

Post by ShadowIllusion » 26 Feb 2014, 19:37

Thanks for the help.
I try to find some tachitoscope, but most of them were too old. So I'm start thinking of buy a LCD with GSYNC or LightBoost.
Meanwhile, there is another hardware I want to ask. It's called Sony hmz t3, I tried to find it's specific, but sony didn't post anywhere. So I just wandering did you guys have any clue about this thing?Like it's gtg or refresh rate?

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Chief Blur Buster
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Re: How to show a pic for exactly 12.5ms? [tachitoscope]

Post by Chief Blur Buster » 06 Mar 2014, 14:11

ShadowIllusion wrote:Thanks for the help.
I try to find some tachitoscope, but most of them were too old. So I'm start thinking of buy a LCD with GSYNC or LightBoost.
Meanwhile, there is another hardware I want to ask. It's called Sony hmz t3, I tried to find it's specific, but sony didn't post anywhere. So I just wandering did you guys have any clue about this thing?Like it's gtg or refresh rate?
The Sony HMZ T3 personal entertainment viewer? I'm not sure. I would not think it is suitable as a tachitoscope.

If you want to build your own tachitoscope from scratch, check this out:
http://display-corner.epfl.ch/index.php/TachistoscopeSetup
Head of Blur Busters - BlurBusters.com | TestUFO.com | Follow @BlurBusters on Twitter

       To support Blur Busters:
       • Official List of Best Gaming Monitors
       • List of G-SYNC Monitors
       • List of FreeSync Monitors
       • List of Ultrawide Monitors

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