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Old 09-12-2018, 12:01 PM   #1
Peterjames
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Default YUV or RGB and Edius working color space

Does Edius 8 and 9 work in YUV or RGB color space internally for processing? IIRC earlier versions of Edius worked in YUV?

Some editing software I believe work in RGB (or YRGB) and have to convert YUV camera files into RGB for edit and grading and then convert on export out to YUV files for TV etc viewing. Does or can this conversion process introduce image quality issues?

If Edius works in YUV are there benefits over those that use RGB (and YRGB) such as color accuracy and also when down scaling UHD to HD?

Thanks Peter
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Old 09-13-2018, 06:06 PM   #2
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Originally Posted by Peterjames View Post
Does Edius 8 and 9 work in YUV or RGB color space internally for processing? IIRC earlier versions of Edius worked in YUV?
YUV also known as: Y'UV, YCbCr, YPbPr, etc. are names for method of encoding video information where there is one luminescence and two color difference channels. The difference is whether you are referring to analog, digital, lin or log signal. EDIUS internally is processes in YCbCr (digital) format.

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Some editing software I believe work in RGB (or YRGB) and have to convert YUV camera files into RGB for edit and grading and then convert on export out to YUV files for TV etc viewing. Does or can this conversion process introduce image quality issues?
Every conversion introduces a very small amount of error. Imagine two rulers: first imperial and the second metric. Each can approximate the other's measurements but it can never be exact. It is a very small error: in 8bit signal the maximum rounding error is 0.19%, in 10bit system it is 0.05% and in 12bit system it is 0.01%. So the question is: Will you see it? Are we talking abut 10's and 100's of conversions to the same signal, or are we are talking about just one on the way in and one on the way out... Also, whatever processing you are going to do in the middle will make the conversion error insignificant.

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If Edius works in YUV are there benefits over those that use RGB (and YRGB) such as color accuracy and also when down scaling UHD to HD?
In my opinion no to accuracy and scaling, but the speed is the advantage YUV has over RGB. YUV has less data to process when compared to RGB. For example: One full HD frame (1920 x 1080 in 8bit 422) in YUV is 4,147,200 bytes and the same frame in RGB is 6,220,800 bytes: 1/3 more data per frame to move and process.

BTW: You keep using YRGB as if it was encoding method, I can't find any technical reference to that. The only reference I can see is a mention of DaVinci's processing method where they add luminescence adjustment to RGB. But all it really means is that they add/subtract the same amount from each of the RGB channels when adjusting the Y to lighten or darken but to keep the same hue, like an offset in this case.
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Old 09-13-2018, 07:04 PM   #3
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Thanks Rob for your very detailed reply. I was not sure if Edius processing was RGB which I gather is not quite so good when downscaling UHD to HD, EDIUS internally processing as you say is in YCbCr so should be better for this.

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BTW: You keep using YRGB as if it was encoding method, I can't find any technical reference to that. The only reference I can see is a mention of DaVinci's processing method where they add luminescence adjustment to RGB. But all it really means is that they add/subtract the same amount from each of the RGB channels when adjusting the Y to lighten or darken but to keep the same hue, like an offset in this case.
My reference to YRGB was to internal processing not encoding to file. As well as Edius 8 I also use Resolve that works in YRGB but try to avoid mentioning competitors software when possible. Thanks Peter

Last edited by GrassValley_PS; 09-14-2018 at 06:45 PM.
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Old 09-13-2018, 08:45 PM   #4
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It is a very small error: in 8bit signal the maximum rounding error is 0.19%, in 10bit system it is 0.05% ...
How will this be calculated?
Thx - kurt
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Old 09-13-2018, 10:08 PM   #5
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How will this be calculated?
Thx - kurt
How to calculate rounding error?

Data is stored as an integer (whole numbers: 1, 2, 3, 4, etc…)

Math rounding rule dictates that if a result of a calculation is less than 0.5 then you round it down, if it is equal or more than 0.5 then you round it up.
For example if a result of a calculation is 78.49 then it will be stored as 78, on the other hand if it is 78.50 then it is stored as 79.
So the maximum possible rounding error here is ±0.4999999999….

Another way to look at it:

78.0 … 78.4999 = 78
78.5 … 78.9999 = 79

To see what that ±0.4999999999…. error represents, you calculate what that number represents over the full range of each system ( * 100 to get the correct % value):

8bit : 0.4999999999 / 2^8 * 100 = 0.19531249996 %
10bit : 0.4999999999 / 2^10 * 100 = 0.04882812499 %
12bit : 0.4999999999 / 2^12 * 100 = 0.01220703124 %
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Old 09-13-2018, 11:34 PM   #6
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Quote:
Originally Posted by 7hbg View Post
How to calculate rounding error?

Data is stored as an integer (whole numbers: 1, 2, 3, 4, etc…)

Math rounding rule dictates that if a result of a calculation is less than 0.5 then you round it down, if it is equal or more than 0.5 then you round it up.
For example if a result of a calculation is 78.49 then it will be stored as 78, on the other hand if it is 78.50 then it is stored as 79.
So the maximum possible rounding error here is ±0.4999999999….

Another way to look at it:

78.0 … 78.4999 = 78
78.5 … 78.9999 = 79

To see what that ±0.4999999999…. error represents, you calculate what that number represents over the full range of each system ( * 100 to get the correct % value):

8bit : 0.4999999999 / 2^8 * 100 = 0.19531249996 %
10bit : 0.4999999999 / 2^10 * 100 = 0.04882812499 %
12bit : 0.4999999999 / 2^12 * 100 = 0.01220703124 %

Thanks:
What I was unsure was how you did the computations with integer values. Now I see you made first a float computation with the integer values and then you rounded the result to get back an integer.
The rest to get % is clear.

// BTW: You know that .499999... (infinite 9s) is math. equal 5.000000... :-).
Regards kurt
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Old 09-14-2018, 06:43 PM   #7
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Let's keep the comments focused on the OP question. All other posts will be deleted.
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Old 09-14-2018, 07:27 PM   #8
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Let's keep the comments focused on the OP question. All other posts will be deleted.
Pat, can GV confirm that Edius 8 and 9 are processing in YCbCr as mention by Rob in reply to my original post. Thanks Peter
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Old 09-15-2018, 02:01 AM   #9
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Pat, can GV confirm that Edius 8 and 9 are processing in YCbCr as mention by Rob in reply to my original post. Thanks Peter

yes, the only software I know of that edits in RGB is Final Cut
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Old 09-15-2018, 08:16 AM   #10
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Thanks Anton.
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