Why -3db gain? - Page 2 at DVinfo.net

Go Back   DV Info Net > Canon EOS / MXF / AVCHD / HDV / DV Camera Systems > Canon HDV and DV Camera Systems > Canon XL and GL Series DV Camcorders > Canon XL1S / XL1 Watchdog

Canon XL1S / XL1 Watchdog
Can't find it on the XL1 Watchdog site? Discuss it here.


Reply
 
Thread Tools Search this Thread
Old December 30th, 2002, 02:46 PM   #16
Retired DV Info Net Almunus
 
Join Date: Dec 2001
Location: Chicago, IL
Posts: 6,943
Andre,
Confucious said: "Never argue with man who have technical reference manual for camera and knows what he read." ...which Don has and does. <g>

Actually, isn't this getting awfully thick and irrelevent to Charles' original question?
__________________
Lady X Films: A lady with a boring wardrobe...and a global mission.

Hey, you don't have enough stuff!
Buy with confidence from our sponsors. Hand-picked as the best in the business...Really!

See some of my work one frame at a time: www.KenTanaka.com
Ken Tanaka is offline   Reply With Quote
Old December 30th, 2002, 04:48 PM   #17
Wrangler
 
Join Date: Feb 2002
Location: Cleveland, Ohio
Posts: 1,929
Well I'm interested in the inner workings of the XL1S.

_____ thick and irrelevant
|
V
__________________
All the best,
Robert K S

Search DVinfo.net for quick answers | The best in the business: DVinfo.net sponsors
Robert Knecht Schmidt is offline   Reply With Quote
Old December 30th, 2002, 04:51 PM   #18
Wrangler
 
Join Date: Feb 2002
Location: Cleveland, Ohio
Posts: 1,929
If the XL1S gain control is analog, why is the knob designed to be discrete adjust (versus being a continuously variable pot)? That is, why can't I turn the knob between settings to get +4 dB etc.?
__________________
All the best,
Robert K S

Search DVinfo.net for quick answers | The best in the business: DVinfo.net sponsors
Robert Knecht Schmidt is offline   Reply With Quote
Old December 31st, 2002, 04:32 AM   #19
Major Player
 
Join Date: Sep 2002
Location: Belgium
Posts: 804
I didn't know that confuscious (+/- 500 B.C.) already knew about the existance of technical ref manuals for camera's...Because I was for over 30 years, toroughly involved in circuit and chip design for simular signal processing, and I know about the strip down exercises to be done for so called ref manuals to make them useable for repair people, I am not impressed by the "interconnected blocks" style wiring diagrams which are published through such channels...Sorry Don. Happy Newyear anyway!
Andre De Clercq is offline   Reply With Quote
Old December 31st, 2002, 05:51 AM   #20
Major Player
 
Join Date: Sep 2002
Location: Belgium
Posts: 804
Because the unusual 9-bit processing mentioned by Don I searched and found some info from Chris Hurd http://www.dvinfo.net/canon/skinny.php. Now I understand why Jeff Donald allways sees banding in the sky on his DV camera(XL1s I suppose) where it is seldon mentioned (although possible)in other DV articles. The XL1s apparently has only a 6-bit equavalent grayscale resolution... of course resampled on a 8-bit structure for the DV format. This makes me also conclude that gamma and WB are done in the (9-bit) digital domain. These are the two processes by which you "loose bits": 2 for gamma (4xgain at black) and 6 db for WB (=1-bit). Other processes ( pixel shift, noise reduction...) don't reduce grayscale resolution.
Andre De Clercq is offline   Reply With Quote
Old January 2nd, 2003, 06:11 AM   #21
Warden
 
Join Date: Mar 2002
Location: Clearwater, FL
Posts: 8,267
That makes a lot of sense. Thanks for doing the research on it. It's very useful information.

Jeff
Jeff Donald is offline   Reply With Quote
Old January 2nd, 2003, 07:02 PM   #22
Wrangler
 
Join Date: Sep 2001
Location: Northern VA
Posts: 4,294
> ... If the XL1S gain control is analog, why is the knob designed to be discrete adjust ...

The gain control is a switch that selects a specific voltage step on a voltage divider. That voltage is sent to the control/logic circuit. Depending on the voltage level you get the differnt gain settings, or automatic gain. The analog gain is selected in descrete steps, which works for video. If the control directly controlled the gain via a potentiometer (like many stereo volume controls) it could introduce noise, especially as it ages and would be hard preseed to provide logic selections as well.

As for the 6-bit grayscale. Not sure how that computes. Would be easy to check. Someone shoot a gray wedge and read the luma levels in the output. 6-bit implies only 64 possible values for the luma signal. The XL1 DSP shows 9-bit input, 8-bit output.

FYIW, the old L2 and Ai-Digital camcorders Hi-8 system used 6-bit for the color portion of their internals DSP.
Don Palomaki is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

Professional Video
(800) 833-4801
Portland, OR

B&H Photo Video
(866) 521-7381
New York, NY

Z.G.C.
(973) 335-4460
Mountain Lakes, NJ

Abel Cine Tech
(888) 700-4416
N.Y. NY & L.A. CA

Precision Camera
(800) 677-1023
Austin, TX

DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > Canon EOS / MXF / AVCHD / HDV / DV Camera Systems > Canon HDV and DV Camera Systems > Canon XL and GL Series DV Camcorders > Canon XL1S / XL1 Watchdog

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



Google
 

All times are GMT -6. The time now is 01:00 AM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2017 The Digital Video Information Network