Q: Why should you care about accurate color decoding on your Blu-ray/DVD player? - AVS Forum
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post #1 of 34 Old 01-23-2012, 08:20 PM - Thread Starter
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A: If you're using the player to calibrate your TV, then incorrect color decoding can potentially foul up the color settings/adjustments on the TV for other inputs/devices.

I mention this because I recently went shopping for a Blu-ray player, and went through 3 different models before finding one that could pass a simple SD color decoding test when upscaling DVDs to HD.

Some players may also output accurate color with one type of media or resolution, but not others. I've tested a number of upscaling DVD players for example, and some could pass color decoding tests at 480i/p, but not when scaling DVDs to 720p or 1080i/p.

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post #2 of 34 Old 01-23-2012, 08:39 PM
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Ok, I'll bite. Which BD players did you test and what were the results?
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post #3 of 34 Old 01-23-2012, 09:00 PM - Thread Starter
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The Panasonic DMPBD75 and Sony BDPS185 failed to pass SD color decoding tests when scaling DVDs to HD in RGB mode. These are both lower-end models. The Sony BDPS185 had a noticeable green push. The Panny had other issues.

The unit which passed the tests (edit: in RGB mode only) was a Sony BDPS580 (the one with built-in WiFi). That model also has a fan though, which was somethin I didn't really want.

I did not test the color decoding with Blu-ray discs btw, only with DVDs.

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post #4 of 34 Old 01-23-2012, 09:59 PM
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Well then I'd just have to buy equipment that are THX certified!

Solution: FREE. Explanation: I will have to charge$ you.

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post #5 of 34 Old 01-23-2012, 10:57 PM
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Buy an OPPO. Problem solved.
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post #6 of 34 Old 01-24-2012, 08:01 AM
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Secrets of Home theater did a great test for this and found that many fail the decoding test including the high end McIntosh and others.

EVRYTHING based on an OPPO passed with flying colors.

http://www.hometheaterhifi.com/techn...roduction.html

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post #7 of 34 Old 01-24-2012, 09:09 AM
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I believe the Panasonic 210/215 does to but can't find the link to the data..

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post #8 of 34 Old 01-24-2012, 09:29 AM
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The tests and resulting article from secrets was great.

My 2 players I use are both from the Sony X70 series (BDP-S370 and BDP-S470.)

Although the BDP-S570 showed a failure to measure 100% correct the errors were small.

In my case,.. I got both my players from Ebay for under $50 shipped so the idea of replacing with Oppo (provided I can get 3D capability from Oppo) isn't too tempting.

Also... Blu Ray is 99.9653% of what I watch so I don't care if dvd playback is skewed or broadcast playback is off. (The only HD broadcast I watch is football and it looks fine.) I also don't even want to try to calibrate 3D. I just calibrate for 2D Blu and the rest has to cope...


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post #9 of 34 Old 01-24-2012, 09:45 AM
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post #10 of 34 Old 01-24-2012, 11:13 AM
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Quote:
Originally Posted by PlasmaPZ80U View Post

How does the PS3 perform in this respect?

The writeup of the PS3 still hasn't appeared, but I tested both an original model, and a slim model, with different firmware versions, and found that you can get the PS3 to pass the data correctly. There is a chart attached showing the different results based on what mode (YCbCr or RGB) and if you select Superwhite or Limited for those modes. It doesn't go into depth on it, but that should help anyone that wants to use the PS3.

The Panasonic 210 is perfect as well if you use Normal mode and don't enable Advanced Chroma. Sony has also released firmware updates for the S570 and S580 since we tested those, so performance might have improved, but I haven't retested them to see.

For the original poster, what did you use to test that it's doing the Rec 601 to Rec 709 color-twist correctly? I had considered testing this but hadn't gotten around to doing so yet.
LL

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post #11 of 34 Old 01-24-2012, 11:36 AM
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Chris,

Always nice to see the experts pop up

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post #12 of 34 Old 01-24-2012, 11:44 AM
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If the player only converts 4:2:0 -> 4:2:2, no scaling, no color space conversion, I guess that the receiver/display have access to all of the information they need in order to do a correct conversion? Are they typically able to?

The biggest question would be bt601 vs bt709. I think that bt601 is generally used for SD and 709 for HD, but is this always true? Can HDMI signal explicitly?

-k
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post #13 of 34 Old 01-24-2012, 11:49 AM
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Quote:
Originally Posted by Smackrabbit View Post

...

Hi Chris

In this chart, it is stated that actual value is equal to R_reference/G_reference/B_reference, but still the delta_e is >0. How can that be?
http://www.hometheaterhifi.com/image...mi-1-large.gif

Did you test consider dithering (if any)? If a sufficiently large flat patch was used, spatial averaging of the output should return the "pre-dithering/quantization" value that we probably are most interested in.

It would also be interesting to see if >8bpc HDMI links actually contain useful information in the lsb (given that the source does any processing that warrants more than the 8 bits of Bluray), or if they are just zero-padded.
Quote:
Originally Posted by Smackrabbit View Post

For the original poster, what did you use to test that it's doing the Rec 601 to Rec 709 color-twist correctly? I had considered testing this but hadn't gotten around to doing so yet.

I think that a really proper conversion would involve BT601 4:2:0 -> BT601 4:4:4 -> rgb -> inverse gamma -> linear 3x3 matrix -> gamma -> rgb -> BT709 4:4:4 ->...

I guess that no-one does all of that, and Poynton claims that this procedure can be simplified with minor errors.

It would also be interesting to know what filter kernels they are using in the 4:4:4/4:2:2/4:2:0 resampling. Simple 2-tap linear interpolation?

-k
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post #14 of 34 Old 01-24-2012, 11:55 AM - Thread Starter
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^Interesting remarks/questions.

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Originally Posted by rovingtravler View Post

Secrets of Home theater did a great test for this and found that many fail the decoding test including the high end McIntosh and others.

EVRYTHING based on an OPPO passed with flying colors.

http://www.hometheaterhifi.com/techn...roduction.html

Thanks for the link to this article, David. For the record, my comments above should not be regarded as an "endorsement" of the Sony S580. The only thing I've tested for so far is color decoding on upscaled DVDs. My primary way of doing that is by looking at color bar patterns like this with only one color component (either red, green or blue) enabled on the TV at a time.



I have not run any other tests yet on the Sony S580 for clipping, WTW, BTB, banding/contouring or resolution issues (e.g. vertical/horizontal multiburst). Nor have I done any tests using full HD resolution Blu-ray patterns. After my experience with the first 3 players though (and reading about issues on the Sony 570 in the Secrets link above), I'll definitely be scrutinizing BD players more closely.

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post #15 of 34 Old 01-24-2012, 12:08 PM - Thread Starter
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Quote:
Originally Posted by Brian Hampton View Post

Blu Ray is 99.9653% of what I watch so I don't care if dvd playback is skewed or broadcast playback is off. (The only HD broadcast I watch is football and it looks fine.) I also don't even want to try to calibrate 3D. I just calibrate for 2D Blu and the rest has to cope...

My situation is basically the reverse. 95% of the discs I own are DVDs, so the color accuracy when upscaling is an important aspect of a player's performance to me.

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post #16 of 34 Old 01-24-2012, 12:21 PM - Thread Starter
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Quote:
Originally Posted by Smackrabbit View Post

Sony has also released firmware updates for the S570 and S580 since we tested those, so performance might have improved, but I haven't retested them to see.

FWIW, I purchased the S580 over the holidays, and have not upgraded the firmware on it yet. I'll check to see what version is currently installed though, and get back to you with that info.

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post #17 of 34 Old 01-24-2012, 12:34 PM
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Quote:
Originally Posted by knutinh View Post

Hi Chris

In this chart, it is stated that actual value is equal to R_reference/G_reference/B_reference, but still the delta_e is >0. How can that be?
http://www.hometheaterhifi.com/image...mi-1-large.gif

This is, I fully admit, the single most confusing thing, and something that always comes up, so I'll break it down as to why it looks that way. All of these patterns have to be encoded at YCbCr 4:2:0 since they are on a Blu-ray disc. In order to get a pattern that has, for example, Red 234, it is going to have corresponding blue and green values as well. These values for the test pattern are always under 16, which for most video cases renders them as virtually insignificant. However, for Red 234, our RGB reference value might be (234, 9, 11), and the value being returned is (234, 10, 11). In that case, there is no error for the Red value, which is what we are looking for, but there is a very, very minute error in green, which causes a dE error still.

I've been working on ways to better process and evaluate this data, and that might include running dE tests where we consider those secondary values, and ones where we don't, and then seeing what the difference is. Since those errors cause only around a dE of 0.2, which is so insignificant as to make it almost meaningless, I wouldn't worry about them myself. That said, some players do get those 100% perfect, and I think we should recognize those players. Some take any value below 16 and make it 16, and while in most cases that will be fine, there is no reason to do that and so recognizing players that don't do that is important.

I hope this clears that up. I could put all the data on the results page, but then it becomes incredibly messy and hard to deal with, and I don't think that makes it better for anyone if they can't read the data. I could also just ignore those numbers, but the last thing I want is someone to accuse me of making the numbers look better by playing around with them instead of being totally accurate.

Quote:


Did you test consider dithering (if any)? If a sufficiently large flat patch was used, spatial averaging of the output should return the "pre-dithering/quantization" value that we probably are most interested in.

It would also be interesting to see if >8bpc HDMI links actually contain useful information in the lsb (given that the source does any processing that warrants more than the 8 bits of Bluray), or if they are just zero-padded.

I haven't really tried the DeepColor testing yet, where something like a color gradient would be more useful than color patches for that to see how it interpolates the values between two figures, but I have thought about the dithering issue. Right now we know that some players dither, and so reference values can be +/- 1 on some players. If I think I notice this going on, I usually check out more points and see if it really is dithering it, as we don't consider dithering to be bad.

I'm starting to advance the test processing to the point that I might be able to sample 9 or 25 points instead of a single point and then get an average and median value from those, which would put to rest any worries about dithering in a sample. That might be the nest target I am for on the test, as it leads to even better results, which is what we want.

Chris Heinonen
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post #18 of 34 Old 01-24-2012, 12:43 PM
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Quote:
Originally Posted by Smackrabbit View Post

This is, I fully admit, the single most confusing thing, and something that always comes up, so I'll break it down as to why it looks that way. All of these patterns have to be encoded at YCbCr 4:2:0 since they are on a Blu-ray disc. In order to get a pattern that has, for example, Red 234, it is going to have corresponding blue and green values as well. These values for the test pattern are always under 16, which for most video cases renders them as virtually insignificant. However, for Red 234, our RGB reference value might be (234, 9, 11), and the value being returned is (234, 10, 11). In that case, there is no error for the Red value, which is what we are looking for, but there is a very, very minute error in green, which causes a dE error still.

I've been working on ways to better process and evaluate this data, and that might include running dE tests where we consider those secondary values, and ones where we don't, and then seeing what the difference is. Since those errors cause only around a dE of 0.2, which is so insignificant as to make it almost meaningless, I wouldn't worry about them myself. That said, some players do get those 100% perfect, and I think we should recognize those players. Some take any value below 16 and make it 16, and while in most cases that will be fine, there is no reason to do that and so recognizing players that don't do that is important.

I hope this clears that up. I could put all the data on the results page, but then it becomes incredibly messy and hard to deal with, and I don't think that makes it better for anyone if they can't read the data. I could also just ignore those numbers, but the last thing I want is someone to accuse me of making the numbers look better by playing around with them instead of being totally accurate.

What do you use for encoding the YCbCr to Bluray? Are you assuming an sRGB-ish 16-235 matrixed using BT601/709?

I thought that it was considered cosher to do anything to levels outside of the 16-235 range? (including clipping). However, for xvYCC they are important.

I fail to see the utility of using rgb primaries in the test. Would it not be equally useful to generate test-stimulus directly in YCbCr, and (if needed) generate a reference rgb output to compare against?

-k
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post #19 of 34 Old 01-24-2012, 12:48 PM
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Quote:
Originally Posted by ADU View Post

The Panasonic DMPBD75 and Sony BDPS185 failed to pass SD color decoding tests when scaling DVDs to HD. These are both lower-end models. The Sony BDPS185 had a noticeable green push. The Panny had other issues.

The unit which passed the tests was a Sony BDPS580 (the one with built-in WiFi). That model also has a fan though, which was somethin I didn't really want.

I did not test the color decoding with Blu-ray discs btw, only with DVDs.

I calibrated my set with a Panasonic BDT-210. Looks great for Blu-rays, DVDs, and OTA.
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post #20 of 34 Old 01-24-2012, 01:24 PM - Thread Starter
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^Good to know.

Quote:
Originally Posted by Smackrabbit View Post

For the original poster, what did you use to test that it's doing the Rec 601 to Rec 709 color-twist correctly?

This is something I've asked a couple times on this a forum (so I guess one more time won't hurt )...

If a player correctly re-matrixes 601 -> 709, then should it pass a simple SD color bar test like the one I posted above (or like you'd find on DVD editions of DVE or AVIA) when upscaling DVDs to HD? Or does the re-matrixing introduce "errors" into the SD patterns?

My assumption has always been that the player should pass the SD tests when upscaling. That seems to fit with my subjective assessments of the color differences. I'm still not 100% sure this is correct though.

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post #21 of 34 Old 01-24-2012, 01:32 PM
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Quote:
Originally Posted by knutinh View Post

I thought that it was considered cosher to do anything to levels outside of the 16-235 range? (including clipping). However, for xvYCC they are important.

I fail to see the utility of using rgb primaries in the test. Would it not be equally useful to generate test-stimulus directly in YCbCr, and (if needed) generate a reference rgb output to compare against?

-k

Kosher means within dietary laws for judaism, but colloquially means simply acceptable.

YCbCr, doesn't say anything about RGB values, it's only the YCbCr values that have nominal ranges. Those values are 16-235 for Y and 16-240 for Cb and Cr. This means many of the legal YCbCr values create values that are outside 16-235 range in the RGB world.

Of course you can encode values outside of the nominal range, and every disc that has a BTB or WTW pattern does this, it's perfectly fine and should work.

xvYCC, uses the fact that some YCbCr values actually create negative RGB values to create extra saturation. So if you have Y:42, Cr:250, Cb:100 it transforms to r235,b-10,g-10 you would end up with a red that was even more saturated than rec709.

I don't know of any pattern generators that support xvYCC nor any calibration software that supports it.

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post #22 of 34 Old 01-24-2012, 01:34 PM
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Quote:
Originally Posted by knutinh View Post

What do you use for encoding the YCbCr to Bluray? Are you assuming an sRGB-ish 16-235 matrixed using BT601/709?

I thought that it was considered cosher to do anything to levels outside of the 16-235 range? (including clipping). However, for xvYCC they are important.

I fail to see the utility of using rgb primaries in the test. Would it not be equally useful to generate test-stimulus directly in YCbCr, and (if needed) generate a reference rgb output to compare against?

-k

You can do content outside of 16-235, and there is commercial content with values that fall outside of this range on the market. Some people will argue that this data shouldn't exist, and some receivers and Blu-ray players will truncate it, but the data can be there, so a player should pass it as it is encoded.

We do test YCbCr as well, and for a player the process of converting YCbCr to RGB should be trivial, but we find that sometimes it is not. Some displays do better when processing RGB instead of YCbCr and so you would want a player that does perfect RGB in this case. Similarly you might have a receiver that handles RGB better, and the same case would apply.

The test patterns were generated by Stacey Spears (of Spears and Munsil). I can't tell you for certain how he created them as I wasn't there for that step.

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post #23 of 34 Old 01-24-2012, 01:37 PM
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Quote:
Originally Posted by Smackrabbit View Post

You can do content outside of 16-235, and there is commercial content with values that fall outside of this range on the market. Some people will argue that this data shouldn't exist, and some receivers and Blu-ray players will truncate it, but the data can be there, so a player should pass it as it is encoded.

Yes, I agree. I think the reason we have this headroom is because the makers of the spec wanted to have some headroom for intermediate processing (filtering/scaling) that might generate overshoots. Guess they wanted a linear signal chain.

For all I know, it is directly inherited from analog signalling standards.
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I don't know of any pattern generators that support xvYCC nor any calibration software that supports it.

I guess a start would be to make a disk of values in the full 0-255 range (properly flagged if Bluray spec says so), set the player in "source direct" and hookup a HDMI analyzer/display to see if the player is transparent wrgt the extended ranges.

-k
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post #24 of 34 Old 01-24-2012, 01:44 PM
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Quote:
Originally Posted by ADU View Post

^Good to know.

This is something I've asked a couple times on this a forum (so I guess one more time won't hurt )...

If a player correctly re-matrixes 601 -> 709, then should it pass a simple SD color bar test like the one I posted above (or like you'd find on DVD editions of DVE or AVIA) when upscaling DVDs to HD? Or does the re-matrixing introduce "errors" into the SD patterns?

My assumption has always been that the player should pass the SD tests when upscaling. That seems to fit with my subjective assessments of the color differences. I'm still not 100% sure this is correct though.

On this I can't really provide you a definite answer until I attempt to test it out. There are color bar test patterns out there that are incorrect, so the first step is making sure the one you are using is known to be good. The second issue is that as Rec 601 and 709 have different primary and secondary points, and white is a different combination between the two, so there could be a chance that during the 601 to 709 conversion you are having a secondary color that is no longer just two primaries fully saturated, but introducing a third color as well, or it isn't fully saturated by both colors.

I really can't answer this one for certain, I'm hoping someone else can, but I can try to take a DVD color pattern (I'll use AVIA or Video Essentials), pass it from an Oppo 93 to an HDMI analyzer and see what I get. That should result in an accurate image, but what those values are I'm not certain.

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post #25 of 34 Old 01-24-2012, 01:51 PM
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Quote:
Originally Posted by knutinh View Post

I guess a start would be to make a disk of values in the full 0-255 range (properly flagged if Bluray spec says so), set the player in "source direct" and hookup a HDMI analyzer/display to see if the player is transparent wrgt the extended ranges.

-k

The trick with xvYCC is that it's not 0-255 for RGB. xvYCC is an amphorous blob of YCbCr values that create negative RGB values. xvYCC really can't be properly represented in RGB space, at least not in discrete bit levels.

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post #26 of 34 Old 01-24-2012, 02:14 PM - Thread Starter
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Originally Posted by Smackrabbit View Post

On this I can't really provide you a definite answer until I attempt to test it out. There are color bar test patterns out there that are incorrect, so the first step is making sure the one you are using is known to be good. The second issue is that as Rec 601 and 709 have different primary and secondary points, and white is a different combination between the two, so there could be a chance that during the 601 to 709 conversion you are having a secondary color that is no longer just two primaries fully saturated, but introducing a third color as well, or it isn't fully saturated by both colors.

I really can't answer this one for certain, I'm hoping someone else can, but I can try to take a DVD color pattern (I'll use AVIA or Video Essentials), pass it from an Oppo 93 to an HDMI analyzer and see what I get. That should result in an accurate image, but what those values are I'm not certain.

Thanks for the reply, Chris. Any further light that you're able to shed on this would be appreciated.

I suspect that the color bar/decoding tests on the 2003 Component video edition of DVE are not 100% accurate btw (though they seem pretty close), which is why I also create and burn my own to DVD in DVD-Video compliant MPEG-2.

FWIW, the pattern posted above is in 75% "full-swing" RGB levels as follows...

Black: 0,0,0
Red: 191,0,0
Magenta: 191,0,191
Green: 0,191,0
Yellow: 191,191,0
White: 191,191,191
Cyan: 0,191,191

I also use patterns with 100% color levels.

If you could correctly convert a pattern like this to 16-235 "studio-swing" DVD-Video and try it out, I'd be very curious to hear your results. (You're welcome to use the one posted above btw.)

ADU
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post #27 of 34 Old 01-24-2012, 04:59 PM
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Quote:
Originally Posted by ADU View Post

Thanks for the reply, Chris. Any further light that you're able to shed on this would be appreciated.

I suspect that the color bar/decoding tests on the 2003 Component video edition of DVE are not 100% accurate btw (though they seem pretty close), which is why I also create and burn my own to DVD in DVD-Video compliant MPEG-2.

FWIW, the pattern posted above is in 75% "full-swing" RGB levels as follows...

Black: 0,0,0
Red: 191,0,0
Magenta: 191,0,191
Green: 0,191,0
Yellow: 191,191,0
White: 191,191,191
Cyan: 0,191,191

I also use patterns with 100% color levels.

If you could correctly convert a pattern like this to 16-235 "studio-swing" DVD-Video and try it out, I'd be very curious to hear your results. (You're welcome to use the one posted above btw.)

I have zero experience in DVD authoring, so I'll need to figure out what patterns I can use that are 100% accurate. Even if I create a pattern using those values, I have no way of knowing that doing the conversion to 4:2:0 will go correctly in a way that will return those exact values when encoded. Factor in that the Blu-ray player is now doing the 601 to 709 twist, and you have an issue knowing:

- Did the original data encode correctly
- Did the player decode the DVD data correctly
- Did the player perform the twist correctly

Since any of those can fail, it means I need a reference point to start from, and creating my own patterns is just going to lead to problems so I need to find out which ones on a DVD are correct already.

Chris Heinonen
Senior Editor, Secrets of Home Theater and High Fidelity, www.hometheaterhifi.com
Displays Editor, AnandTech.com
Contributor, HDGuru.com and Wirecutter.com
ISF Level II Certified Calibrator, ReferenceHomeTheater.com
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post #28 of 34 Old 01-24-2012, 08:00 PM - Thread Starter
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Quote:
Originally Posted by Smackrabbit View Post

I have zero experience in DVD authoring, so I'll need to figure out what patterns I can use that are 100% accurate...

Fair enough. I haven't tried all the different calibration discs out there, so maybe someone else can offer some input on that. (Or perhaps I can figure out some way to upload an MPEG or DVD image of my patterns, though I can't be sure my MPEG encoder is 100% accurate either).

After reading your article on the Sony S570, I decided to go back and do a more thorough series of DVD tests on the S580 in both RGB and YCbCr modes, using 25%, 50%, 75% and 100% color patterns like the one posted above. And I found that the S580 does indeed appear to be pushing some green in both the 4:2:2 and 4:4:4 YCbCr modes when upscaling DVDs to 1080i/p. (Since I mainly used the player on an older Sony HDTV with a DVI/RGB input, I apparently didn't check the YCbCr modes as closely as I thought.)

The color decoding patterns checked out ok though in the RGB color mode with all 4 tests. The color decoding on this player is very similar to my old Sony NS77H HDMI DVD player (which also pushes green in the YCbCr mode, but does a pretty good job on color decoding tests in the RGB mode).

I also ran a couple other DVE DVD tests on the S580 in RGB/1080i/p mode, and FWIW it does appear to pass both BTB and WTW info (so there's no clipping of the standard 16-235 DVD color palette), and it also passes the full vertical resolution on DVDs in that mode. Did not get a chance to do a thorough test for banding/contouring issues though. (Looks like the RGB mode may be preferable on this model, at least for upscaling DVDs.)

The software version on the S580 player is M07.R.0263.

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post #29 of 34 Old 01-24-2012, 10:36 PM
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Quote:
Originally Posted by sotti View Post

The trick with xvYCC is that it's not 0-255 for RGB. xvYCC is an amphorous blob of YCbCr values that create negative RGB values. xvYCC really can't be properly represented in RGB space, at least not in discrete bit levels.

My suggestion was actually to test the player using "YCbCr"/xvYCC as input and output, just checking that all codes are retransmitted and that the handshaking over HDMI is such that the display/receiver knows what it is getting.

-k
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post #30 of 34 Old 01-25-2012, 05:19 AM
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I love this topic and hope I understand it eventually.

Here's a thought though...

If you watch mostly (upconverted) DVDs,... does it make sense to use a up converting DVD player instead of a Blu Ray player?

Maybe having 2 settings on the display is useful (one aiming for 601 and the other for 709.)

I always assumed that if you tuned with a calibration DVD you would optimize best for DVD (601) and if you tuned with a Blu Ray calibration disc you would optimize best for HD (709.)

Forgive me if I'm still very confused but I like all the disussions about this... I am confused and hopefully I'll learn something.

-Brian
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