red bias & red gain - AVS Forum
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post #1 of 12 Old 04-07-2012, 06:15 AM - Thread Starter
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Hi,
Whats the difference in calibration between bias and gain? When use one or the other?
I have an Optoma HD20...
Thanks in advance
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post #2 of 12 Old 04-07-2012, 06:22 AM
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Originally Posted by evo5 View Post

Hi,
Whats the difference in calibration between bias and gain? When use one or the other?
I have an Optoma HD20...
Thanks in advance

Far from an expert but gain effects the entire ire range from my understanding. Bias affects the lower ire range for the most part.

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post #3 of 12 Old 04-07-2012, 06:26 AM - Thread Starter
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Originally Posted by chunon View Post

Far from an expert but gain effects the entire ire range from my understanding. Bias affects the lower ire range for the most part.



Thank you chunon...
What means for ire range?
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post #4 of 12 Old 04-07-2012, 06:27 AM
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They are typically interactive in they effect everything to some extent, but
Bias is for the low end 10-50 and gains are for 50-100. You would start out a 2 point gray scale adjustment by displaying a 30% white pattern and adjusting the RGB Bias to get you as close to D65 for that stimulus then display an 80% pattern and adjust the RGB gains to get close to D65. Then take readings of the complete 10 point scale and adjust either/or to get everything as flat as possible even if your 30 and 80 are now slightly off.
If you do not have an accurate meter and software do not mess with these adjustments as they can not be properly set by eye.

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post #5 of 12 Old 04-07-2012, 06:31 AM - Thread Starter
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Originally Posted by airscapes View Post

They are typically interactive in they effect everything to some extent, but
Bias is for the low end 10-50 and gains are for 50-100. You would start out a 2 point gray scale adjustment by displaying a 30% white pattern and adjusting the RGB Bias to get you as close to D65 for that stimulus then display an 80% pattern and adjust the RGB gains to get close to D65. Then take readings of the complete 10 point scale and adjust either/or to get everything as flat as possible even if your 30 and 80 are now slightly off.
If you do not have an accurate meter and software do not mess with these adjustments as they can not be properly set by eye.

Thank you airscapes...
Will work Spears & Munsil disc calibrator?
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post #6 of 12 Old 04-07-2012, 06:35 AM
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Originally Posted by evo5 View Post

Thank you chunon...
What means for ire range?

IRE is a term from the old Analog days (I think it stands for International Radio Engineers ) but it refers to the amount of luminous stimulates (how bright) a gray pattern is. A 10 point gray scale consists of 10 patterns of white, from video white which is 100% luminous down to 10% which is 10% above Video black and all the other percentages in between 10%,20%,30%,40%,50%,60%,70%,80%,90%,100%

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post #7 of 12 Old 04-07-2012, 06:45 AM - Thread Starter
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Thank you!!!!!
Spears & Munsil is a good calibrator? Any other?
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post #8 of 12 Old 04-07-2012, 11:48 AM
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Think of bias as the Brightness (AKA black level) control.
Think of Gain at the Contrast (AKA picture) control,

Bias or brightness is made up of a combination of RGB.

Gain or contrast is made up of a combination of RGB.

Bias affects the near black part of the image, Gain affects the near white part of the image.

Bias and gain interact.

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post #9 of 12 Old 04-07-2012, 01:14 PM - Thread Starter
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Originally Posted by Gregg Loewen View Post

Think of bias as the Brightness (AKA black level) control.
Think of Gain at the Contrast (AKA picture) control,

Bias or brightness is made up of a combination of RGB.

Gain or contrast is made up of a combination of RGB.

Bias affects the near black part of the image, Gain affects the near white part of the image.

Bias and gain interact.

Thank you, Gregg
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post #10 of 12 Old 04-07-2012, 03:26 PM
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Originally Posted by airscapes View Post

IRE is a term from the old Analog days (I think it stands for International Radio Engineers ) ---[snip]


Old analog days, indeed.

IRE stands for the Institute of Radio Engineers. It is now known as the Institute of Electrical and Electronics Engineers (IEEE.)

Some of us are members. Some of us even were members of the both the IRE and the American Institute of Electrical Engineers (AIEE) before the merger of the two and the subsequent name change in the early 1960s.

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post #11 of 12 Old 04-07-2012, 03:38 PM
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Originally Posted by LarryInRI View Post

Old analog days, indeed.

IRE stands for the Institute of Radio Engineers. It is now known as the Institute of Electrical and Electronics Engineers (IEEE.)

Some of us are members. Some of us even were members of the both the IRE and the American Institute of Electrical Engineers (AIEE) before the merger of the two and the subsequent name change in the early 1960s.

Larry

No offense meant..
I guess the point I was trying to making is calling something "20 IRE" does not really properly describe a white pattern at 20% stimulus.

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post #12 of 12 Old 04-07-2012, 03:57 PM
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Originally Posted by airscapes View Post

No offense meant..
I guess the point I was trying to making is calling something "20 IRE" does not really properly describe a white pattern at 20% stimulus.


No offense taken.

The IRE unit was defined to indicate relative amplitude of the voltage in an amplitude modulated TV signal waveform.

Long before digital TV, when digital signal technology was being developed in the 1960s and 1970s, the IRE unit was used only because it was convenient. It still has its uses but not in the context of HDTV.

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