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Old 02-21-2020, 12:34 PM   #1
dmkvideo
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Default Primary Color Correction does not satify the ITU-R BT specs

Excuse my bad English.

I am an electronic engineer and I participated in the development of the ITU-R BT standards. Edius has always satisfy the full specs buts there is a clipping issue in this filter. I ask to correct this damageable situation.

Because many reader dont know works the math of YUV (and it's digital YCbCr sub part), I do first a very little introduction.

If you think that YUV has the same gammut and color depth than sRGB because they have the same bit depth, you are not right. YUV encodes colors in the same way as the LAB, XYZ and CIE 1931 color spaces with specific coeficients and complicated color transform math. I go not in the details but you must know that the YUV color space is wider than the sRGB color space and can even code for negative RGB value (see https://en.wikipedia.org/wiki/XvYCC, a good but incomplete introduction). Furthermore, even if you respec the Zebra at 100% to shoot in 16-235 range for Y, there are peeks in the bright saturated colors wich have RGB color values far above de max. 255 range. For Ex. my Sony has shoot Rec.709 YCbCr=244, 63, 207 (bright red part in a lava flow) = RGB 365.63!!, 219.75, 126.08. I have very often G or B=290. This values are above 1023 in the Videoscopes.

Edius has a full YUV and filter core so that there is never clipping of the wider YUV color space. Furthermore, Edius is fully comptible with the xvYCC color space. There is thus never clipping of the datas (even if you shoot at 109 IRE) to the lower gammut sRGB space limited to 255/1023 or even to 235/960 like by other NLE's. This is OK.

But the Primary Color Correction filter does no work in the good way. This filter that seems to work in RGB instead of YUV and clips the colors at 255 even if you don't apply a LUT and that all the cursors are to the default. I ask to update this filter to work in full range YUV with no clipping and to accept Shaper LUT's. Another way is to add an negative gain input cursor and a output cursor to gain the signal back up to his original level. This workaround will only produce little banding artifacts in a 8 bit project and can compromise real time but it's not as bad as clipping. At the moment, this filter don't satisfy the ITU-R BT wich says: "the signal under 0 and above 1 may never be clipped during production, mastering nor in the intermediate files". The dramatic consequences of clipping are for ex.: hue shift, greenish sky, not possible to decently import REC.709 in the wider Rec.2020 gammut or in HDR because the bright saturated Rec.709 colors where sadly clipped before the conversion.

I ask also to extend the upper scale of the Scopes to 1535 so that you can immediately see what is above 255/1023 like in the previous Edius Scopes.

TIP: the full unclipped YUV range is send to the external monitor trough the Intensity Pro 4K. The Panasonic, Philips and probably the Sony monitors and TV's display the above 255 RGB colors without clipping. You see thus exactly what you have shoot. This is not the case with almost all the other NLE's, even Resolve. Switch never to another NLE!

Computer: Intel i7 8700K with Intel Graphic 630 + Blackmagic Intensity Pro 4K
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Old 02-21-2020, 02:18 PM   #2
LewS
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Does this have anything to do with the Scene Light/Display Light setting in the PCC which changes the clipping level?
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Old 02-21-2020, 05:47 PM   #3
DigitalDave
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Demuynck your English is great!
I regularly send TVads to UK Broadcasters, who maintain Strict compliance to EBU R103.
Back in 2016 I fell FOUL of Gamut and got a FAIL. (isn't the English language wonderful)

This lead to Forum member Rob Wiejak developing a plugin to identify errors.
http://rgbgamut.zabcia.ca/

He and several members also provided LUTS for correction.

Amongst the things we discovered was simply adding a New Blue OFX Bridge was enough to correct many clips.
This is the UK spec:
Levels must be in accordance with ​ITU BT.601 ​ for SD content, ​ITU BT.709 ​ for HD content,* and ​EBU R103-2000 ​ recommendations:** * Luma = Level 16-235 (not RGB 0-255 level), equivalent to 0% - 100% or** 0mV - 700mV. Chroma = Level 16-240, equivalent to maximum 100% RGB.* * All content should be upper/first field dominant throughout and must be free of encoding artefacts, dropout, glitches, blocking, interlace issues or excessive aliasing and considered broadcast quality throughout.*

Since being able to IDENTIFY errors and then correct, I have not had a single fail.

I am not an engineer. I am but a simple editor who only understands Pass and Fail, but I also know that Broadcasters across the US, Japan and other parts of the civilised and tech savvy world, use systems based around Edius. I cannot and do not believe they are pushing out stuff that is out of spec.
David
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Old 02-21-2020, 06:16 PM   #4
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If you go to this Sticky thread and look at post #28, you will see the information that David is talking about.
https://forum.grassvalley.com/forum/...ad.php?t=36907
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Old 02-24-2020, 07:12 PM   #5
Seemedia
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Quote:
Originally Posted by DigitalDave View Post
Demuynck your English is great!
I regularly send TVads to UK Broadcasters, who maintain Strict compliance to EBU R103.
Back in 2016 I fell FOUL of Gamut and got a FAIL. (isn't the English language wonderful)

This lead to Forum member Rob Wiejak developing a plugin to identify errors.
http://rgbgamut.zabcia.ca/

He and several members also provided LUTS for correction.

Amongst the things we discovered was simply adding a New Blue OFX Bridge was enough to correct many clips.
This is the UK spec:
Levels must be in accordance with ​ITU BT.601 ​ for SD content, ​ITU BT.709 ​ for HD content,* and ​EBU R103-2000 ​ recommendations:** * Luma = Level 16-235 (not RGB 0-255 level), equivalent to 0% - 100% or** 0mV - 700mV. Chroma = Level 16-240, equivalent to maximum 100% RGB.* * All content should be upper/first field dominant throughout and must be free of encoding artefacts, dropout, glitches, blocking, interlace issues or excessive aliasing and considered broadcast quality throughout.*

Since being able to IDENTIFY errors and then correct, I have not had a single fail.

I am not an engineer. I am but a simple editor who only understands Pass and Fail, but I also know that Broadcasters across the US, Japan and other parts of the civilised and tech savvy world, use systems based around Edius. I cannot and do not believe they are pushing out stuff that is out of spec.
David
That's right Dave. At the end I protect the sequence by putting the PCC filter, where RGB closes the space at 16-235
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Last edited by Seemedia; 02-24-2020 at 09:28 PM.
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Old 03-21-2020, 09:06 AM   #6
DigitalDave
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The Perfect example of what we in the UK call a Seagull.
Flies in
DUMPS
Flies off
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