| Author |
Message |
AFryia
Joined: 09 Mar 2006
Posts: 965
Location: S.E. Michigan VPH-G70Q
|
| Posted: Sat Mar 15, 2008 4:32 pm Post subject: Bias vs. Brightness Adjustment |
|
|
I'm a little confused on the BIAS and Brightness setup. My PJ is a G70 so there is no G2 control, strictly BIAS and Brightness.
With my colorimeter (HFCR) I can drop the BIAS of the Blue to almost zero and balance the R&G. I can run Blue at say 80 and still match the R&G for good white/grey balance. How do I determine the proper settings?
Does lowering the BIAS equate to lowering the Brightness? Which do you set first? What do you look for other than white balance?
|
|
| Back to top |
|
 |
Sonynut
Joined: 08 Aug 2006
Posts: 367
Location: Bradford,PA
|
| Posted: Sat Mar 15, 2008 5:11 pm Post subject: |
|
|
BIAS is basically brightness adjustment, but for each color individually. BRIGHTNESS adjusts all three at once.
Personally(I do not have a colorimeter), I adjust BIAS rather high(almost all the way up on all three) to achieve even and visible gray -no tinting- at lower IRE, but not true black. I then drop BRIGHTNESS way down to get my true blacks. Not sure if this helps shadow detail or not, but it definitely works to keep my brightness adjustment value low.
_________________
1272 Stack coming soon:)
|
|
| Back to top |
|
|
macgyver655
Joined: 22 Aug 2007
Posts: 8508
|
| Posted: Sun Mar 16, 2008 3:39 pm Post subject: |
|
|
|
I'll give you a method to try that I have used on many devices with great success. First you need no signal or black signal to projector. Set bias to full on all 3. Now turn briteness all the way full. If you have good tubes you should see a raster on all 3 tubes looking into the lens. Now slowly turn down the master briteness until one of the rasters disappear. Now useing the bias, turn down the remaining color raster's until each of them disappear. Now to double check your adjustment, turn up the master briteness and all 3 rasters should come on at the same time. Adjust master briteness back down and all 3 should go off at the same time. Its worth a try with nothing to loose. How do you blacks and greys look now?
|
|
| Back to top |
|
|
Zebu Fellenz
Joined: 21 Dec 2006
Posts: 2567
|
| Posted: Sun Mar 16, 2008 4:29 pm Post subject: |
|
|
|
Sounds like a good way to set black level, I'll try it now
|
|
| Back to top |
|
|
AFryia
Joined: 09 Mar 2006
Posts: 965
Location: S.E. Michigan VPH-G70Q
|
| Posted: Sun Mar 16, 2008 8:34 pm Post subject: |
|
|
| macgyver655 wrote: | | How do you blacks and greys look now? |
Pitch Black!
Maybe too much. I believe that is what they call crush? Grey scale is good, much improved after de-focusing the Blue tube.
I have a follow up question.
My Bias setting is scaled 0-255(max). My Bias setting are in the 40-80 range with Bightness set to 45 on a scale 0-100. With your method I would start by turning all Bias to full on, max setting (255)? Just curious why not start at a mid range setting for Bias?
|
|
| Back to top |
|
|
macgyver655
Joined: 22 Aug 2007
Posts: 8508
|
| Posted: Sun Mar 16, 2008 9:02 pm Post subject: |
|
|
| AFryia wrote: | | macgyver655 wrote: | | How do you blacks and greys look now? |
Pitch Black!
Maybe too much. I believe that is what they call crush? Grey scale is good, much improved after de-focusing the Blue tube.
I have a follow up question.
My Bias setting is scaled 0-255(max). My Bias setting are in the 40-80 range with Bightness set to 45 on a scale 0-100. With your method I would start by turning all Bias to full on, max setting (255)? Just curious why not start at a mid range setting for Bias? |
The reason to start with bias at full on is because as tubes get older and with master briteness at full on a tube may not produce a raster at 50 % bias. So then you wouldn't know where to start. I have see some tubes (lower output ones) that wouldn't even produce a raster at full on for bias and briteness. As far as your number of 255 seeming high.....Its just a number. If the manufacture wanted the scale to be 1-10, where 10 was full bias and 10 was the same as your 255, it wouldnt sound like a big number then.
You could try with your bias at 125 (mid) to start and briteness at full, and if you had a raster on all 3 tubes you would find that as you dropped the master briteness for the first color to disappear, it would be double the briteness number on your scale then if you started at 255 bias.
You may find that at 50% bias and full briteness, one or more tubes may not have a raster.
It still comes out the same except for the number of your master briteness when all 3 tubes loose there raster.
I think I explained this so you could understand it but if your still not sure I'll try again.
|
|
| Back to top |
|
|
Gino
Joined: 22 Apr 2006
Posts: 1363
Location: Trinity Beach, AUSTRALIA
|
| Posted: Tue Mar 18, 2008 1:16 am Post subject: |
|
|
Bring up a pluge pattern for setting your black level. Once you've set that right, then you do your grey scale calibration.
_________________
( B ) ( G ) ( R ) Blendzilla Down Under ( R ) ( G ) ( B ) - Tubes of Fury
|
|
| Back to top |
|
|
Tinman
Joined: 09 Mar 2006
Posts: 1326
Location: Carson City Nevada
|
| Posted: Tue Mar 18, 2008 3:05 am Post subject: |
|
|
I set brightness at 50 (or 60 on some sets) and store that. THEN adjust Bias (cutoff) for each tube to JUST go black on a black image.
You DON'T adjust bias at full brightness. Usually 50%. NEC's recomend 60 but I personally use 50%.
The rest is then adjusted for greyscale using the DRIVE, WHITE,or whatever they are called for your particular brand. However, the Bias and Drive interact, so must be adjusted several times back and forth for optimal.
You THEN use the pluge pattern and fine adjust the global Brightness control so black and blacker than black are the same.
Marc
_________________
This space for rent.
|
|
| Back to top |
|
|
macgyver655
Joined: 22 Aug 2007
Posts: 8508
|
| Posted: Tue Mar 18, 2008 2:16 pm Post subject: |
|
|
| Tinman wrote: | I set brightness at 50 (or 60 on some sets) and store that. THEN adjust Bias (cutoff) for each tube to JUST go black on a black image.
You DON'T adjust bias at full brightness. Usually 50%. NEC's recomend 60 but I personally use 50%.
The rest is then adjusted for greyscale using the DRIVE, WHITE,or whatever they are called for your particular brand. However, the Bias and Drive interact, so must be adjusted several times back and forth for optimal.
You THEN use the pluge pattern and fine adjust the global Brightness control so black and blacker than black are the same.
Marc |
Your not adjusting bias at full brightness, your just starting there and then lowering it from there until you loose your first color, then useing bias to loose the remaining too. If your tubes are strong enough to produce a raster at 50% brightness then great, you can do like you say, and its basically the same as I said in the beginning. I described a method for all crt devices in general. And as far as factory recommendation's...... Thats fine if the projector has new or fairly good tubes, but after some time, like all other crt's you'll have to start with the brightness up higher. As I said your only starting at full. then reduceing from there. You may make it all the way down to 30% brightness before you loose the first color, then reduce bias for the remaining.
If you start at 50% brightness with weaker tubes, you wont even be able to produce a raster at all with bias.
The key is for all three tubes to come on and go off at the same time useing the brightness control, regardless of the numbers.
|
|
| Back to top |
|
|
Gino
Joined: 22 Apr 2006
Posts: 1363
Location: Trinity Beach, AUSTRALIA
|
| Posted: Wed Mar 19, 2008 12:11 am Post subject: |
|
|
| Tinman wrote: |
You THEN use the pluge pattern and fine adjust the global Brightness control so black and blacker than black are the same. |
After adjusting your global brightness, youll need to do more tweaking to your grey scale as this will change things again
_________________
( B ) ( G ) ( R ) Blendzilla Down Under ( R ) ( G ) ( B ) - Tubes of Fury
|
|
| Back to top |
|
|
Frank D
Joined: 20 Jun 2006
Posts: 73
|
| Posted: Wed Mar 19, 2008 4:31 am Post subject: |
|
|
| macgyver655 wrote: | | I'll give you a method to try that I have used on many devices with great success. First you need no signal or black signal to projector. Set bias to full on all 3. Now turn briteness all the way full. If you have good tubes you should see a raster on all 3 tubes looking into the lens. Now slowly turn down the master briteness until one of the rasters disappear. Now useing the bias, turn down the remaining color raster's until each of them disappear. Now to double check your adjustment, turn up the master briteness and all 3 rasters should come on at the same time. Adjust master briteness back down and all 3 should go off at the same time. Its worth a try with nothing to loose. How do you blacks and greys look now? |
Wont you bias change again once you use it to adjust for gray scale at 30 ire thereby throwing it off in relation to what you have stated above?
|
|
| Back to top |
|
|
perisoft
Joined: 29 Aug 2007
Posts: 2920
Location: Ithaca, NY
|
| Posted: Wed Mar 19, 2008 3:53 pm Post subject: |
|
|
Presumably this all interacts with G2 as well? Makes me think there's something off about my G2 (though I set it according to the Barco manual) because I can see the screen start to get gray (ie, rasters lighting up the screen surface visibly) at anything over about 20 brightness, with the biases set default. If I put brightness at 100 it'd light up the whole damned room!  Is something messed up there? My tubes aren't exactly stellar...
_________________
|
|
| Back to top |
|
|
|
|
