homeGeek CultureWebstoreeCards!Forums!Joy of Tech!AY2K!webcam

The Geek Culture Forums


Post New Topic  New Poll  Post A Reply
my profile | directory login | | search | faq | forum home
  next oldest topic   next newest topic
» The Geek Culture Forums   » Other Geeky Stuff   » Ask a Geek!   » Computer video question

 - UBBFriend: Email this page to someone!    
Author Topic: Computer video question
Ti
Assimilated
Member # 941

Member Rated:
5
Icon 1 posted January 22, 2006 19:53      Profile for Ti   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
Okay, here is a tough question for you video hardware nuts.

I'm trying to get a MacMini to produce an RGB video 400 horizontal x 234 vertical resolution NTSC signal with a 15.7khz refresh rate.

Anybody know of any hardware that can do this? Is it possible with OSX to send that sort of a resolution?

Thanks in advance,

Kevin

--------------------
Check out my webpage/blog/review stash
www.logichigh.com

Posts: 377 | From: Sunnyvale, CA | Registered: Oct 2001  |  IP: Logged
Zwilnik

Solid Nitrozanium SuperFan!
Member # 615

Member Rated:
4
Icon 1 posted January 23, 2006 02:00      Profile for Zwilnik   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
Sounds like a job for a video converter of some sort. If you use the TV adaptor for the mini, it will give you a PAL or NTSC signal via composite or S-Video that might be easier to convert to that particular resolution.

--------------------
The Universe is entirely made up of elements.
The most important of which is the element of surprise.

Posts: 1040 | From: West Sussex, UK | Registered: Dec 2000  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted January 23, 2006 04:00      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
Ti__________________________Ok heres the scoop. The 15.7 you are refering to is not the refresh rate it is the speed of the horizontal scan. This is the speed all TVs used up until about 1970, Then as VCRs came into use, the manufacturers slowed down the sweep speed so that VCRs would not tear the top edges of the screen. All anilog TV stations broadcast at 60 frames, 15750 Hz and 535 lines modulated into the AM part of the Channel, most VCRs out put 30 frames 7875 Hz and 267 lines most people cannot see the loss of frames. There are still some TVs that have two speed clocks one to use on VCRs and one for the full signal.
So any device that puts out a NTSC should have the TV standard. 60 Frames 15750 Hz sweep rate and 535 lines, actually you only get 500 lines as 35 are used to return the sweep generater back to the top of the screen.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5836 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
Ti
Assimilated
Member # 941

Member Rated:
5
Icon 1 posted January 23, 2006 18:24      Profile for Ti   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
Sorry, you are right that is the horizontal scan rate I was refering to 15.75khz...

The screen is a 400x234 LCD display, that takes the NTSC signal. If you feed it any other resolution then it looks fuzzy or doesn't display very readable. I'm looking for a readable, albiet small display. From what I have seen from scalers and converters there aren't any that can put out that resolution spefically, and even if there were, sending the wrong resolution to the scaler would just end up with a scrunched or screwy image.

So ultimately I think I'm going to need to use the MacMini to produce the proper video signal. I've done a little research on it, and so far here's what I've got:

Macmini DVI to composite video out and plug the composite video into a Composite to SCART adapter because the device I'm trying to hook into uses a specially wired SCART connector for the RGB-NTSC signal. Then I'll use ScreenResX to force the output from the MacMini to be the right resolution and sweep rate.

Any A/V or Macheads see any reason why that wouldn't work?

Thanks for all your thoughts, and help!

Kevin

--------------------
Check out my webpage/blog/review stash
www.logichigh.com

Posts: 377 | From: Sunnyvale, CA | Registered: Oct 2001  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted January 24, 2006 10:06      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
Ti_______________I would think that any screen resolution that used sixty frames per second, would work. It might even work at one twenty but then you would have twice as much info. I would think that you do not want to change frame rate as that is when some problems arrise. I would go with the highest resolution that you can put on sixty frames per second, that is thirty five frames faster than your eye can see.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5836 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
zesovietrussian
SuperBlabberMouth!
Member # 1177

Icon 1 posted January 24, 2006 12:07      Profile for zesovietrussian     Send New Private Message       Edit/Delete Post   Reply With Quote 
Try finding a Mac equivalent of a Windows utility called Powerstrip. That program lets you use all sorts of weird resolutions that normally aren't supported by the video card driver.
Posts: 1094 | From: Boston | Registered: Mar 2002  |  IP: Logged
TomtheMacMan
Geek Larva
Member # 2127

Member Rated:
5
Icon 1 posted January 24, 2006 19:17      Profile for TomtheMacMan     Send New Private Message       Edit/Delete Post   Reply With Quote 
I'd say that you should just grab the Mac Mini-Video adaptor and feed it in there, and put it on 640x480. Just try it. It should actually look decent. It may not be incredibly readable, but it should work. Remember, all NTSC video is 720x480, which in square pixels (Aka computer pixels) is 640x480. If this monitor's anything like the LCDs I've used, it should perform well under this resolution, which is about double what it actually has in pixels. It may not be perfect, but it works. Look into small touchscreen LCDs, they run at 800x640 sometimes. Just make sure that the box reads that. If you're stuck with the LCD, nothing's going to pipe it to the LCD at native resolution. It'd be out of NTSC spec.

Scan rate really doesn't apply at all here. If it's over 60hz, the video converter takes it back down. Change scan rates all you want, same result.

--------------------
-Tom

Posts: 20 | Registered: Apr 2003  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted January 27, 2006 03:50      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
Back to the topic__________________NTSC is not a digital standard it is anilog. There are 500 lines of picture information 250 odd and 250 even lines, each line is sent one at a time. That is why the first attempts at computer generated vidio looked so bad. If you were to go to a high end TV store and watch a very large screen TV (projection or CRT) you will actually see the lines especially if it is from a VCR. Because the VCR when it recorded the program threw out the even numbered lines. The less work the digital converter has to do is better so go with the highest resolution you can get at 60 frames, because that is the native frame rate of NTSC.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5836 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
drunkennewfiemidget
BlabberMouth, a Blabber Odyssey
Member # 2814

Member Rated:
4
Icon 1 posted January 27, 2006 05:18      Profile for drunkennewfiemidget     Send New Private Message       Edit/Delete Post   Reply With Quote 
To go into a little more detail:

TheMoMan is absolutely correct (as usual).

You may remember Hz from electronics class. It's a measurement of oscillations per second.

On a television or monitor, the refresh in Hz is the number of times the screen is updated per second.

60Hz means the screen is updated 60 times a second.

The funny thing though, is interlacing.

When a screen is interlaced (which all cable and televisions are unless you have progressive scan turned on), you actually only get 30 FULL pictures per second.

The image is redrawn 60 times, but each time, it's only half the screen.

The first update will update scan lines 1, 3, 5, 7, 9, 11, 13, etc.

The second update will update scan lines 2, 4, 6, 8, etc.

On a progressive scan, every line is updated every time, so you get 60 full new images per second.

Your computer monitor is inevitably in 85Hz or 75Hz or something non-interlaced, which is the same as progressive scan. That means it updates the whole screen 85 or 75 times respectively per second.

And I would imagine nobody here is still running on an interlaced monitor. The flickering would make you go nuts that close to the screen for any lengthy amount of time.

Of course, IANAL, YMMV, IMNHSO, IRAH.

Posts: 4897 | From: Cambridge, ON, Canada | Registered: Jun 2004  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted January 27, 2006 07:15      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
DNF_______________________Thanks for the vote of confidence, lets go back even farther when the term base band vidio was the standard for black and white TV then came Color what a nightmare, there was not enough room during the 190 nano seconds of B/W info to put in the color. The color for each line was broadcast later during retrace, now you are saying how can that be because they both have to hit the screen at the same time. Enter the delay line, at first it was eleven feet of coax between the last vidio IF stage and the Horizontal timing Oscilator so that the color image could catch up with the B/W image, now it is handled in a chip, back then there was the delay line. Because not all stations used the same standard one was proposed and it became NTSC so that all broadcasters and manufacturers could build to the same rules. It does not matter how wide the TV screen is the sweep takes 190 nanoseconds then retrace. Now with the new digital TVs and High Def I have to go and relearn how the picture is going to be painted onto the screen.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5836 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
Ti
Assimilated
Member # 941

Member Rated:
5
Icon 1 posted January 27, 2006 12:53      Profile for Ti   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
Fascinating. But it does seem all to fit. From other peoples experience with this unit (which I have since ordered and will soon find out first hand what works and what doesn't), they said that 640x480 works, but looks terrible. It seems that the 400x234 oddball resolution is what is listed for the hardware and what works best. I dropped the numbers into Switch Res X and interestingly enough produced a 64hz refresh rate.

Thanks for your input, I hope it all works out [Smile]

Kevin

--------------------
Check out my webpage/blog/review stash
www.logichigh.com

Posts: 377 | From: Sunnyvale, CA | Registered: Oct 2001  |  IP: Logged


All times are Eastern Time  
Post New Topic  New Poll  Post A Reply Close Topic    Move Topic    Delete Topic next oldest topic   next newest topic
 - Printer-friendly view of this topic
Hop To:

Contact Us | Geek Culture Home Page

2015 Geek Culture

Powered by Infopop Corporation
UBB.classicTM 6.4.0



homeGeek CultureWebstoreeCards!Forums!Joy of Tech!AY2K!webcam