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# Blog: Since When Is Black and White Green?

I found the following blog while researching ITU Recs. 601 and 709 in the hope of learning more about what might be causing some Sony SXRD owners to report a dreaded greenish tinge, especially on SD material: http://whatsonhdtv.blogspot.com/2006...ite-green.html

...the blogger basically hypothesizes that the greenish tinge is being caused by incorrect color matrix conversion somewhere along the way.

Does the blogger's theory have merit? I'd appreciate any insight from those in the know...

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Quote:
Originally Posted by 1920x1080

Does the blogger's theory have merit? I'd appreciate any insight from those in the know...

Not for black and white material. In both 601 and 709 matrices, Cb and Cr are equal to 128 when there is absence of color. Both matrices will output the same RGB values when Cb and Cr are 128. Just look at the equations:

601
R = Y + 1.371(Cr - 128)
G = Y - 0.698(Cr - 128) - 0.336(Cb - 128)
B = Y + 1.732(Cb - 128)

709
R = Y + 1.54(Cr - 128)
G = Y - 0.459(Cr - 128) - 0.183(Cb - 128)
B = Y + 1.816(Cb - 128)

When Cb and Cr are 128, both equations become R = G = B = Y.

Ron
Green blob is a problem with SXRD light engines, not incorrect color matrix conversions.
Quote:
Originally Posted by eapleitez

Green blob is a problem with SXRD light engines, not incorrect color matrix conversions.

...and lumping everything into the "green blob" problem is an oversimplification.
FWIW, There's a lot of so-called "B&W" programming that suffers from poor encoding at some point along the way to your set. Case(s) in point: episodes of the original "Twilight Zone" (on SciFi) and "The Andy Griffith Show" (from one of my local stations.) ...
Quote:
Originally Posted by HDTVChallenged

FWIW, There's a lot of so-called "B&W" programming that suffers from poor encoding at some point along the way to your set. Case(s) in point: episodes of the original "Twilight Zone" (on SciFi) and "The Andy Griffith Show" (from one of my local stations.) ...

I wonder if there is something odd going on with DVD authoring? I note much excess green on many British TV-on-DVD titles. I have very slight excess green on other material with my system: Oppo 971 (DVI)->Westinghouse 37w3.

-Bill
I think it was still a calibration issue. The blogger did not specify what Plasmas he had. Some have different gray scale memories for different scan rates - so his gray scale for 1080i might have been OK, but 480i was off.

He also mentioned that he had issues getting these plasmas calibrated.
Quote:
Originally Posted by wmcclain

I wonder if there is something odd going on with DVD authoring?

If so, it wouldn't be the first (or last) time. One well known and respected calibration disk has a documented red contamination in some of it's greyscale patterns.
Quote:
Originally Posted by dr1394

Not for black and white material. In both 601 and 709 matrices, Cb and Cr are equal to 128 when there is absence of color. Both matrices will output the same RGB values when Cb and Cr are 128. Just look at the equations:

601
R = Y + 1.371(Cr - 128)
G = Y - 0.698(Cr - 128) - 0.336(Cb - 128)
B = Y + 1.732(Cb - 128)

709
R = Y + 1.54(Cr - 128)
G = Y - 0.459(Cr - 128) - 0.183(Cb - 128)
B = Y + 1.816(Cb - 128)

When Cb and Cr are 128, both equations become R = G = B = Y.

Ron

Thank you Ron, quite clear. But how about when color information is present? The coefficients for 709 are "less negative" than for 601, so for any given value of Y, the values of R, G and B are larger with 709 than they are with 601, with G having the greatest difference. Given this, if something in color were encoded with 601 but decoded with 709, wouldn't the resultant values of R, G and B be higher that they should be, with G having the greatest difference?
Quote:
Originally Posted by 1920x1080

I found the following blog while researching ITU Recs. 601 and 709 in the hope of learning more about what might be causing some Sony SXRD owners to report a dreaded greenish tinge, especially on SD material: http://whatsonhdtv.blogspot.com/2006...ite-green.html

...the blogger basically hypothesizes that the greenish tinge is being caused by incorrect color matrix conversion somewhere along the way.

Does the blogger's theory have merit? I'd appreciate any insight from those in the know...

The green tinge I complain about with my Sony A2000 is not present with black and white material. My previous TV had the problem of green streaks in B&W material but my A2000 looks great with B&W.

With my A2000 some peoples faces are too green and soemtimes you see green in the shadows of faces.
Quote:
Originally Posted by 1920x1080

Thank you Ron, quite clear. But how about when color information is present? The coefficients for 709 are "less negative" than for 601, so for any given value of Y, the values of R, G and B are larger with 709 than they are with 601, with G having the greatest difference. Given this, if something in color were encoded with 601 but decoded with 709, wouldn't the resultant values of R, G and B be higher that they should be, with G having the greatest difference?

Yes.

http://www.avsforum.com/avs-vb/attac...chmentid=32137

Ron
Quote:
Originally Posted by HDTVChallenged

If so, it wouldn't be the first (or last) time. One well known and respected calibration disk has a documented red contamination in some of it's greyscale patterns.

That's true (if your speaking of AVIA ) and a good example of how things get blown out of proportion around here. That "contamination" can't be detected by eye, at least not mine. Example, who can see the difference between .xxx8 and .xxx1
Quote:
Originally Posted by 1920x1080

Thank you Ron, quite clear. But how about when color information is present? The coefficients for 709 are "less negative" than for 601, so for any given value of Y, the values of R, G and B are larger with 709 than they are with 601, with G having the greatest difference. Given this, if something in color were encoded with 601 but decoded with 709, wouldn't the resultant values of R, G and B be higher that they should be, with G having the greatest difference?

Yes but only if there is color present. If it's just B&W it should only be Y, so there should be no error.

In addition to the colorbars that ron posted, the illustrations at the bottom of this page are with real images showing matrix mismatches:

Notice how white portions are unaffected, while strongly colored portions are visibly altered when a matrix mismatch occurs.

This is also why display red push problems are NOT solvable with grayscale alterations.
Quote:
Originally Posted by holtzd

The green tinge I complain about with my Sony A2000 is not present with black and white material. My previous TV had the problem of green streaks in B&W material but my A2000 looks great with B&W.

With my A2000 some peoples faces are too green and soemtimes you see green in the shadows of faces.

I have same problem with my 50A2000. I have October build date. The green tinge is driving me crazy. The questio is, what can we do to correct it???
I have the same problem. Has there been any news?
sounds like a gray scale issue...either make the gray scale more blue and hide or get it calibrated to D65 gray.

There is also a chance of it being the Sony LCOS green blob issue. I have seen this 20-30 times now. The last time I saw it was on a GEN 2 XBR LCOS. It was mild but it was there.

regards

Gregg
I have the XBR2 and I don't think its the green blob issue. When I look at a black and white source the screen is quite homogeneous. It is also very close to D65. It has to be something else, I just don't know what.
Quote:
Originally Posted by holtzd

...With my A2000 some peoples faces are too green and soemtimes you see green in the shadows of faces.

A few months ago, after reading an article that discussed how the iris affected color rendition in the Sony Pearl, I tuned to a channel notorious for greenish 5 o'clock shadows, paused an obvious example and started fiddling with my KDS-60A2000. To make a long story short, I found that the iris, green bias and white level controls interacted with each other with respect to the greenish 5 o'clock shadows. It took awhile, but IIRC, I basically ended up going from medium to auto-2 on the iris, cutting G-bias by a few steps and boosting white level a few steps relative to settings I had achieved using DVE, SpyderTV and InHD, etc.
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