Author Topic: BUG v1.02.11 Color decoding is wrong most of the time  (Read 14856 times)

May 07, 2009, 01:08:44 PM
Read 14856 times

Hokeysmoke

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If you go to the bottom of this web page you can see what incorrect color decoding looks like.
http://www.sigmadesigns.com/public/Support/chromaticity.html

Videos are almost always encoded using component video (YCrCb) in order to save space compared to RGB.  Therefore, in order to be displayed the component video must be decoded back into RGB.  The decoding standard for Standard Definition sources such as DVDs is known as BT.601 and the one for HDTV is BT.709.  Therefore, you would expect the WDTV to decode HDTV video files using BT.709 unless told otherwise by flags in the source file.  However, it does not.  It uses BT.601.

The actual behavior is as follows:
If the video file is flagged as BT.601, then it will be decoded using BT.601.
If the video file is flagged as BT.709, then it will be decoded using BT.709.
If the video file is not flagged, then it will be decoded using BT.601.

Unfortunately, most video files are not flagged.  Since almost all HDTV content is made using BT.709, then most of these files will be decoded incorrectly.

The above behavior is correct if this product were a DVD player, but almost all Blu-ray, HD-DVD, and ATSC set-top boxes act differently.  They assume that all HD content is BT.709 unless the flags say otherwise.

Note that this error in decoding occurs internally before the signal even gets to the HDMI transmitter.  So you cannot fix it at the display.
« Last Edit: October 01, 2009, 06:53:45 PM by Hokeysmoke »

May 07, 2009, 03:12:38 PM
Reply #1

Monkeyface66

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On the "feature requests voting site" the WD Team accepted this feature request :


"Black level and HDMI color space options in the settings menu to adjust picture quality"

http://wdtv.uservoice.com/pages/17442-general/suggestions/182951-black-level-improved



Maybe the issue with the wrong BT.601 color will be coincidentally fixed then .......

May 07, 2009, 04:44:11 PM
Reply #2

Hokeysmoke

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Unfortunately, these are two separate issues.  The color decoding issue is happening in the Sigma Designs chip, and the black level issue is happening in the HDMI transmitter.  But one can always hope...
« Last Edit: May 07, 2009, 07:36:28 PM by Hokeysmoke »

May 07, 2009, 07:30:05 PM
Reply #3

Hokeysmoke

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By the way, this bug is not exclusive to the WDTV.  It also affects the NMT products, and I have reported that bug to Syabas as well.  It would be interesting to see who fixes it first.

(Yes, I do have both products now)

May 28, 2009, 10:38:27 AM
Reply #4

Hokeysmoke

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This is still not fixed in 1.02.08.

June 17, 2009, 11:40:50 AM
Reply #5

Hokeysmoke

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This is still not fixed in v1.02.10.  Updated thread title.

June 26, 2009, 01:35:22 PM
Reply #6

GuyWD

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Hi Hokeysmoke, can you please send me a link to an untagged file that reproduces this issue? I would appreciate it.

June 29, 2009, 09:38:43 AM
Reply #7

Hokeysmoke

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Go to http://www.spectracal.com/downloads.html and download the AVCHD version.  This is a suite of test patterns called AVS HD 709 and the one I linked to is the version 1.2b (at least as of this morning) which is unflagged.  The file is a DVD UDF .iso file.  The file with all of the color decoding patterns is 00005.m2ts.  You can copy that directly to the WDTV and it will play fine.

The newer version is 1.3 and is flagged for BT.709, and can be found here: http://www.avsforum.com/avs-vb/showthread.php?t=948496

You can use a green filter with any of the color bar or decoder patterns to see that the color brightness of green is too high, or you can directly see the green brightness problem using the color brightness ramp pattern which is about 6 minutes into the clip.  In the unflagged version the top two green bars are clipped no matter how you set the display's contrast control, which indicates a problem in the YCbCr conversion to RGB.

Let me know if you need any more information.  I also have some MPEG2 files that I made myself with various flag settings.  I'd be happy to send them to you.

By the way, of the 34 HD-DVD and Blu-Ray discs I checked, only 8 or 24% had BT.709 flagged.  So the WDTV would decode the colors incorrectly the vast majority of the time.  Also, about 50% of the off-air ATSC recordings I have are unflagged.
« Last Edit: June 29, 2009, 10:19:39 AM by Hokeysmoke »

July 01, 2009, 03:29:15 PM
Reply #8

Hokeysmoke

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Here's some more information that may be helpful.  Since both the NMTs and the WDTV suffer from the same color space conversion issue, I've linked below two threads from the NMT forums.  There is a lot of useful discussion from myself and others, including a successful attempt by a developer on another platform to write an application to test the issue.  Not everything is pertinent, but the root cause probably is the same on both products.

http://www.networkedmediatank.com/showthread.php?tid=19366
http://www.networkedmediatank.com/showthread.php?tid=20381

July 02, 2009, 12:10:20 AM
Reply #9

sparky909

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Hi,

Just a quick note - anyone know if this issue occurred in earlier versions of firmware also? e.g. 1.02,1.03...etc...?
Im on old firmware and wondering if its a dealbreaker for upgrading to v10firmware.

many thanks! sparks

July 02, 2009, 07:29:46 AM
Reply #10

Hokeysmoke

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Since this is a bug in the default behavior of the SDK from Sigma Designs, it is likely to have existed from day one.

July 02, 2009, 12:00:06 PM
Reply #11

khkg

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Is there any simple way to properly tag my .MKV collection for 709?

July 03, 2009, 03:51:03 PM
Reply #12

Hokeysmoke

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I know of no easy way to modify the colorimetry flags without remastering.

July 06, 2009, 01:43:09 PM
Reply #13

khkg

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I know of no easy way to modify the colorimetry flags without remastering.

Darn.  Not hopeful that this is going to be resolved anytime soon by either WD or Sigma.
 

July 15, 2009, 03:51:18 PM
Reply #14

Hokeysmoke

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Here's a link to a file that also shows the problem.  Every second it switches from BT.709 flagged to unflagged.  Anyone, even with a completely incorrectly calibrated display, should be able to see the difference.  The correct colors only appear when the "BT.709 Settings" image is displayed.

http://www.cypheros.de/files/Testbild_colour_description_alternating_120sec.ts
« Last Edit: July 16, 2009, 09:48:40 AM by Hokeysmoke »