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Why the lines???


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#1 David Cunningham

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Posted 30 September 2013 - 09:31 AM

Not sure if anyone can recommend a solution or even explanation.

 

I have been using this footage as an example of Super 8 2K reversal scanning on the LaserGraphics ScanStation:

 

 

The problem, you'll see it in the very first seconds, is the odd horizontal (almost interlacing looking) lines, especially on the outer edges of his red sweatshirt.  

 

I have even tried youtube with a 2K Prores 4444 10GB file.  It's much more subtle on youtube, but it's STILL there.

 

Where is this coming from and can I get rid of it?  It's not there at all in the original.  The original is beautifully sharp... almost a perfect Super 8 reversal scan except maybe some dynamic range issues and over-exageration of the red.  The grain is beautifully resolved and the original Prores 4444 2K looks amazing here on my desktop.

 

Thoughts?

 

Dave


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#2 David Mullen ASC

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Posted 30 September 2013 - 10:44 AM

I can't see any lines, not even watching in HD on Vimeo.


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#3 Phil Rhodes

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Posted 30 September 2013 - 10:48 AM

Also not seeing it. Can you post a full-resolution (or crop therefrom), uncompressed PNG file demonstrating the problem?

 

It strikes me that you may just be seeing the colour subsampling inherent to the sort of compression used by YouTube and Vimeo, which is often most obvious on the edges of highly saturated subjects like that. If so, there's nothing you can do about it - that's what internet video looks like.

 

An example:

 

post-29-0-63540700-1292716082.png


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#4 David Cunningham

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Posted 30 September 2013 - 12:46 PM

Hi Phil, That's exactly what I'm seeing.  That's extremely annoying!


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#5 David Cunningham

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Posted 30 September 2013 - 12:48 PM

Hi Mr Mullen,

 

Much respect for all your work and humbled and grateful to be able to speak with you on this forum.

 

Take a look at his left shoulder (the right side of the image for you).  You get those very lines Phil is talking about.

 

Dave


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#6 David Cunningham

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Posted 30 September 2013 - 01:02 PM

You can compare it to:

 

 

Much less of it going on.  It actually almost looks like aliasing the closer I look at it.


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#7 Stephen RK

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Posted 19 October 2013 - 02:37 PM

i think the problem is at the aspect ratio. try cropping it. 


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#8 Justin-Bendo

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Posted 13 December 2013 - 04:13 AM

Phil is right, it's chroma subsampling.

 

Film is RGB, but most codecs are Y CrCb (sometimes abbreviated as YUV).   RGB is converted by a mathematical formula into a luma channel and two chroma channels, which are sampled at 1/2 or 1/4th of the luma (full) resolution (4:2:2 or 4:1:1).  

 

So your 1920 * 1080 Cr and Cb channels, if sampled into 4:1:1, are both actually only 480 * 270 !  

Hence the horrible blockiness, particularly of red because it's the 'widest' wave in the color spectrum.

And the blue channel is generally the noisiest because it's the smallest/narrowest in the color spectrum.

 

The low resolution chroma due to chroma subsampling is why it's extremely difficult to key 4:1:1 and 4:2:2 material without serious help.

 

You can't get rid of it on YouTube, they control their compression encoding settings.  

You can change the playback Quality settings to 720HD, but that's about it.


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