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benareeno
Joined: 22 Mar 2006
Posts: 1614
Location: ottawa, canada
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| Posted: Tue Sep 14, 2010 7:15 pm Post subject: blanking...what is it for? how to manipulate with powerstrip |
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and why more blanking for higher resolutions? I've never quite understood this one...what is the logic behind it?
Also, what parameters in a powerstrip timing do I manipulate to reduce blanking?
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akajester
Joined: 09 Jul 2008
Posts: 934
Location: Wisconsin
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| Posted: Tue Sep 14, 2010 8:58 pm Post subject: |
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do you mean front porch and back porch? That controls the amount of blank lines you want in front or behind the projected image.
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benareeno
Joined: 22 Mar 2006
Posts: 1614
Location: ottawa, canada
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| Posted: Tue Sep 14, 2010 9:34 pm Post subject: |
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in front or behind? What do you mean?
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akajester
Joined: 09 Jul 2008
Posts: 934
Location: Wisconsin
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Ile
Joined: 09 Mar 2006
Posts: 1491
Location: Jyväskylä, Finland
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| Posted: Tue Sep 14, 2010 9:44 pm Post subject: |
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Blanking is display feature to blank crap from picture edges. It was good for standard video, there was all kind crap for example colorburst and text tv lines etc.
Porches are what you are after, here's some info.
http://en.wikipedia.org/wiki/Back_porch
There is back and front porch settings for horizontal and vertical direction in Powerstrip.
Projector deflection and black restoration circuits need certain duration for different timings to operate correctly. When higher resolutions are used, also timing duration have to be higher. So that pulse last as long that with lower resolution.
Simplified example.
I'm assuming this projector need timings that last 10% of one horizontal scanline, to keep this simple.
Back and front porches (/) and sync width (!) takes 10% each of one scanline duration. Numbers are actual pixels in your picture.
/1234567/!
Now two times bigger resolution
//12345678901234//!!
Porches and sync width need to be two pixel wide to get same 10% duration.
Scott have posted some mathematical formulas for Marquee timings.
Most projectors also have jailbars (raster ringing) in left edge if too small porches are used. When there is porch before actual picture scanline have time to stabilize before it.
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Wed Sep 15, 2010 7:22 am Post subject: |
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is this why 720p from my Faroudja scaler comes up really narrow? 576p comes up full screen and so does 1080i.
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benareeno
Joined: 22 Mar 2006
Posts: 1614
Location: ottawa, canada
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| Posted: Wed Sep 15, 2010 5:38 pm Post subject: |
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yes indeed...
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ecrabb
Forum Moderator
Joined: 13 Mar 2006
Posts: 15909
Location: Utah
TV/Projector: JVC RS40, Epson 5010
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| Posted: Wed Sep 15, 2010 6:37 pm Post subject: |
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There's vertical blanking interval or VBI...
http://en.wikipedia.org/wiki/Vertical_blanking_interval
A gap of time (used to allow for retrace) between the end of the last line of one frame of video and the beginning of the first line of the next frame of video.
SC
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