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Sony XDCAM PXW-FS7 / FS5
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Old June 17th, 2016, 11:06 PM   #1
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Nasty compression macroblocking against blue sky

I'd like to draw your attention guys to what I call a "white line compression artefact" problem and sincerely ask you for some help. Ever since I first noticed it, it keeps coming back with all lenses I have (and I'm using 4 of them); it doesn't depend on the recording format (although most noticeable in 4K and QFHD) - but it's present regardless of bitrate and codec flavor (XAVC-I as well as L-GoP) or fps (50 as well as 25). I can notice it in both HG and Slog material..

It's still present in the same part of the frame (upper half), and has a form of what looks like a very thin white line crossing the blue sky perfectly horizontally. To be honest, I'm not 100% positive it's never present elsewhere - but whenever I have blue sky in my scene will it appear. Upon closer inspection, what looks like ever so thin "line" on a PC screen turns out to be compression errors in the form of macroblocking along the said "line"; it's almost like the blue color is not present inside (a white "hole" surrounded by macroblocking)...

I uploaded a quick and dirty sample of my original short clip (straight from camera) here:

Mail a Big File to Matobo - Your File

- and some full size screen grabs for enlargement and inspection here:

Mail a Big File to Matobo - Your File

Mail a Big File to Matobo - Your File

Just please enlarge one of those stills and you will see what I mean by "horizontal line artefact" - it will be easier then to locate it in the video sample (see pic).

Please note that what may go unnoticed on a computer screen is very clearly visible on my 50" UHD TV. This is something much below the picture quality standard I expected from the FS7!

So I'm very kindly asking you guys for your opinions, and some suggestions on what my options are. Of course, my camera is still under warranty - but how do I convince Sony service anything is wrong with the camera, if I didn't convince you? Please help!

Piotr

PS. My biggest concern is the suspicion there is a flaw in my FS7's sensor - otherwise, why should macroblocking (or any other compression artefact) be created along a precisely horizontal line, and seemingly only on the blue background color?

PPS. I forgot to mention that when such a "line" of macroblocking appears, it's not fixed to a given scene location - as when I pan camera (e.g. down or sideways), it follows the camera movement so it stays in the very same position in relation to the frame. This is why originally I suspected my lens - but since it happens with any of my 4 lenses, it's even more probable it has something to do with the sensor...
Attached Thumbnails
Nasty compression macroblocking against blue sky-line-smear-artefact.png  

Last edited by Piotr Wozniacki; June 18th, 2016 at 12:59 AM.
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Old June 18th, 2016, 05:07 AM   #2
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Re: Nasty compression macroblocking against blue sky

Just to add my own comment, while waiting for others to chime-in:

1. Apart from the evident whitish (purplish?) line, the entire blue sky are is heavily blocked; again: expected better from the 500 Mbps XAVC-Intra codec!

2. As to the "line" itself: when looking at the black contrasty wire below it, and then moving my eyes away - I can "see" sort of its "echoes" in the form of white lines appearing and momentarily disappearing on the sky area; these are of course phantom images our brain creates... But the electric current conveying them from my eye to my brain is real; could it be possible that a similar mechanism of "digital echo" is the real reason of my "white line artefact"? With the difference that even if it isn't a picture of an existing object(s), unlike my sight illusion it actually gets recorded, and makes the codec break creating blockiness... The analogy is spoiled though by the fact my eye illusionary "lines" are parallel to the black wire, while the line is always horizontal.

Just a thought...
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Old June 19th, 2016, 04:35 AM   #3
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Re: Nasty compression macroblocking against blue sky

I for one am stunned with the artefacts seen in this image. At one stage I thought it may even be horizontal banding like you see when domestic fluorescent lighting is used and is slightly out of phase with the shutter, possibly in this shot via 50/60Hz power line interference with the camera or something. But probably not.

See the attached pic where I have downloaded one of your frame images in Photoshop and accentuated what is there in the red channel. (It's the blue channel that is famously noisy when it comes to image sensors ... and is politely well behaved this time.)

Definitely some image artefacting here.

Andrew
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Nasty compression macroblocking against blue sky-red-channel-image-artefacting.jpg  
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Old June 19th, 2016, 09:26 AM   #4
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Re: Nasty compression macroblocking against blue sky

Thanks Andrew; at least I will have something to show to Sony PrimeSupport...

Piotr
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Old July 25th, 2016, 11:39 PM   #5
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Re: Nasty compression macroblocking against blue sky

So I thought guys I owe you some update, after so many of you engaged in the debate in this thread - in one or another way Therefore I'm baking it up, and here is the story:

After making sure that I as not hallucinating, and the "faint white line across the sky" was really present in my footage (BTW it was just the macroblocking and loss of color due to the codec errors) - I notified Prime Support service, sending them the original clip. It took them almost 2 weeks to admit something is definitely wrong, but they would need my camera for testing. I postponed sending my still brand new camera for who knows how long, and continued using it in the normal fashion - of course checking for similar artefacts in all my footage - but this time during grading only, and with the Cinema-style preview full screen preview on my 50" UHD TV, using Resolve...

With lots of footage gathered over the last 2 months, I can positively say the codec breaking only occurs in material shot using CineEI mode, and Slog3 curve with S-Gamut3.Cine color space - I didn't try Slog2 yet, but it definitely doesn't happen in my HG footage! This alone makes me even more reluctant to send the camera in, as it looks more and more like a codec rather than hardware issue... But I'd like to make sure, so I'm again asking you guys to help me make 100% sure it's a codec issue in Slog3 - and this is only possible if you carefully check your own footage, and find similar artefacts. Casue if it's really the codec at fault, it should be present in your footage as well, right?

Now - where to look for it: whenever you have a bright area of blue sky, and some contrasty objects at both (left and right) sides of it, the codec is prone to produce something like on my 2 pics (artificial horizontal stripe of macroblocking between those contrasty edges and sort of connecting them with what may look like a thin line on a small display across the sky; yes I did emphasize them by playing with color curves and levels, but isn't Slog3.S-Gamu3.Cine supposed to give us more freedom of stretching the picture to the limits? ).

Sorry - for some reason, could upload the images here, here are the links:

https://www.dropbox.com/s/pxvyn5w8g7...mage4.jpg?dl=0
https://www.dropbox.com/s/h8g10j1y1d...mage3.jpg?dl=0
https://www.dropbox.com/s/dm932e2gj0...mage1.jpg?dl=0

Piotr

PS. I have no idea whether the semi-horizontal wire plays any role here...
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Old July 26th, 2016, 08:14 AM   #6
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Re: Nasty compression macroblocking against blue sky

Hi Piotr. Does it appear in all players outside your NLE?
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Old July 26th, 2016, 02:30 PM   #7
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Re: Nasty compression macroblocking against blue sky

Hi Nigel,

I never rendered out such a convoluted grade, but why wouldn't it? Also - with my "normal" renders (i.e. ones where there is no posterization and other weird effects) of the Slog3 footage does show severe pixel business in the very same areas which I showed as exhibiting codec breaking effects...

Piotr
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Old July 27th, 2016, 11:43 AM   #8
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Re: Nasty compression macroblocking against blue sky

Might be worth taking an untouched clip into something like Catalyst Browse just to be 100% sure this is a camera issue.
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Old July 28th, 2016, 12:17 AM   #9
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Re: Nasty compression macroblocking against blue sky

Here you go, Nigel:
https://www.dropbox.com/s/aq3j29cvhe...052_1.MXF?dl=0

Please not that although the clip shows the scenery I've always used for testing all my cameras, it is NOT the same clip I've taken the linked-to frame grabs from. You must try and fine a frame with this "'faint horizontal line" between the wooden bran and the birch, just below the electric cable - than play with it in your grading/cc app. The reason I uploaded this particular clip (with the offending artifacts not being THAT obvious) has simply been its small size vs. my lousy upload Internet connection speed :(

Piotr
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