Vertical Stepping

Elvis Deane

Elvis Deane

Active member
Just wrapping up work on a short film with some green screen shots, and I've run into a bit of an issue, was wondering if anyone had some ideas. After pulling a key on certain shots (well most really), I've gotten this vertical stepping effect across my actor.
green.jpg



It's almost not noticeable when viewed against the original green, but really jumps out when I key it and throw it against a white background (which is what I'm using for most of these shots).
white.jpg


Is this something we did wrong with some camera setting (shutter speeds, detail coring, whatever), or just an artifacting thing with DVCPRO 100 that I have no control over?

It isn't a problem I noticed on another project when I captured footage straight to FCP, and then keyed in After Effects. For this one we shot to P2 cards and used Raylight to convert. Could be that I just overlooked it the last time.
 
Well a 2 pixel horizontal blur on the alpha channel fixed it, but if there is another way around it in camera, I'd still love to know.
 
DVCProHD, while much nicer than HDV or DV, still compresses color by half which can lead to some stair stepping.
 
I used Keylight in both cases, my workflow the other time was recording straight to FCP, converting to a PNG compressed Quicktime, and then key in After Effects on my PC.
 
It was 720p, which is why I was surprised that there'd be any sort of stepping. I keyed out a ton of interlaced footage a few years back, and even after getting Ultimatte AdvantEdge it was still a huge pain, so I was hoping I'd never have to deal with that sort of thing now that I'm only shooting progressive.

Thanks for that procedural matte tutorial, I read it before but a refresher is always good.
 
Hi Elvis... Bottom line is that HVX 720 is much worse than HVX 1080 for keying.

This is a very commonly seen artifact of the macroblocking... more visually "bad" than the same artifacting if you had shot 1080. I knew it was 720 the moment I saw it. There really is no easy fix for this that works in all cases. This error will kill any semi-tranlucent area you're trying to key.

Here is an example from another thread that shows the difference between 1080 and 720p in the compression/artifacting arena...

http://ftp.datausa.com/imageshoppe/outgoing/HVX_TESTS/720_wipeTo_1080.mov

Regards,
 
The shoulder area is a little out of focus and that causes a blur between your pixels of the shirt and that of the green screen. You could post filter the footage and sharpen it a pixel and that would help. Also most keying programs have a threshold filter or adjustment that will allow you to fine tune your key on bllury areas. Green screen material/subjects should be as in focus as possible not to mention as high rez as possible so 1080 would be better. Just some thoughts, good luck.



Elvis Deane said:
Just wrapping up work on a short film with some green screen shots, and I've run into a bit of an issue, was wondering if anyone had some ideas. After pulling a key on certain shots (well most really), I've gotten this vertical stepping effect across my actor.
green.jpg



It's almost not noticeable when viewed against the original green, but really jumps out when I key it and throw it against a white background (which is what I'm using for most of these shots).
white.jpg


Is this something we did wrong with some camera setting (shutter speeds, detail coring, whatever), or just an artifacting thing with DVCPRO 100 that I have no control over?

It isn't a problem I noticed on another project when I captured footage straight to FCP, and then keyed in After Effects. For this one we shot to P2 cards and used Raylight to convert. Could be that I just overlooked it the last time.
Click to expand...
 
hubertuber said:
Green screen material/subjects should be as in focus as possible not to mention as high rez as possible so 1080 would be better. Just some thoughts, good luck.
Click to expand...

In the thread on 1080 vrs 720p we've been looking at some of the issues regarding compression differences between HVX recorded 720p and 1080... the 1080 material has more resolution, but more importantly has a finer and more pleasing compression pattern making it superior to 720p for this sort of work.

Regards,
 
Elvis Deane said:
Just wrapping up work on a short film with some green screen shots, and I've run into a bit of an issue, was wondering if anyone had some ideas. After pulling a key on certain shots (well most really), I've gotten this vertical stepping effect across my actor.
green.jpg



It's almost not noticeable when viewed against the original green, but really jumps out when I key it and throw it against a white background (which is what I'm using for most of these shots).
white.jpg


Is this something we did wrong with some camera setting (shutter speeds, detail coring, whatever), or just an artifacting thing with DVCPRO 100 that I have no control over?

It isn't a problem I noticed on another project when I captured footage straight to FCP, and then keyed in After Effects. For this one we shot to P2 cards and used Raylight to convert. Could be that I just overlooked it the last time.
Click to expand...


The little corners in your key was indeed a problem with old Raylight, but it's fixed in release 2.0. The problem was (if anybody wants to know) in the filtering of the chroma across 16-pixel boundaries. The new Raylight always filters across the entire scan line (in Raylight Blue).
 
mvb said:
The little corners in your key was indeed a problem with old Raylight, but it's fixed in release 2.0. The problem was (if anybody wants to know) in the filtering of the chroma across 16-pixel boundaries. The new Raylight always filters across the entire scan line (in Raylight Blue).
Click to expand...

Hi Marcus... you should know by now that we always "want to know" the smallest of details on the "details"... :)

Anyway, I decided to revisit some older bluescreen tests I did back in May using the new Raylight version, and yes, the "notches" are gone! This is true with both 720p and 1080 material. This effect was less apparent in 1080 because of the overall larger image, but it was still there.

So, with the goal of showing exactly the differences, I prepped a series of images showing the matte of a bluescreen foreground... how CineForm ConnectHD handled it, Raylight 1.05 and Raylight 2.01. Also I do a "difference" test between those versions of Raylight (REALLY shows off the notching effect) and a "difference" between 2.01 Raylight and the ConnectHD version.

http://ftp.datausa.com/imageshoppe/outgoing/HVX_TESTS/STILLS/RAYLIGHT_CINEFORM_BLUESCREEN.png

The results show that Raylight is clearly the choice for a cleaner matte over CineForm. The CineForm matte has thin vertical lines in the grey areas which give a "buzz" effect to the matte edges.

In the interest of fairness, this was a version of ConnectHD from May, so if David Newman is interested in extending my license for a couple days, I'd be glad to update this image with his latest/greatest codec version as well.

Good job Marcus!
 
Jim,

build 18 is very old, where up to build 33 now for Connect HD . Also you didn't mention what encoder options you used (progressive vs interlaced, the quality setting, and any conversion/scaling filters you may have used.) Download the latest Connect HD 3.2, it should automatically give you 15-days. If not, PM me and I'll send you a link.
 
Thanks David, I'll do that straight-away and update the png of the comparison. I assumed that once you downloaded and finished a trial, that was it.

The footage was 720PN, 24fps. I converted it way back then as 960 by 720, not full raster 1280 by 720. From memory, the quality was the best possible. I see those vertical edge artifacts in material converted as full raster, and also in 1080 material...

I'm also interested in how Edius, FCP and Avid handle the conversion and how both Raylight and CineForm stack up to those... it's amazing how much the coding and approaches impact the quality of the final image...
 
Okay, deleted old ConnectHD and Cineform codec, installed 3.23 version... double checked my settings... "large", "progressive", only difference for tonight, I scaled to 1280 by 720 (since Raylight was doing the same thing).

Interesting, the resulting AVI is right shifted by 1 pixel or more compared to the RAYLIGHT (1280 by 720), or a ConnectHD AVI at native (960 by 720) resolution. I'm pretty sure this isn't an error with my setup in AE, but an actual physical offset. Could this be?

Codec quality is the same as the version I used in May in terms of the fine vertical pattern in the alpha channel grey areas...
 
Jim,

Please send be your source material, so I can reproduce this and determine if you have made a misstep. If the is a scaling error we will be sure to fix it.
 
I sent David the original files and he figured out what I was seeing... remember the old issue with DV codecs? Some were designed to be pleasing "presentational" codecs and blurred the chroma of the 4:1:1 image, similar to the S-VID or component out's on higher end DV decks? Others were "generational", designed to be copied over and over and kept the chroma as originally sampled.

In essence, that's what's happening here, only with 4:2:2. CineForm is more "generational" and Raylight is more "presentational" (my terms, hopefully reasonably accurate).

A very slight blur on just the blue channel fixes the issue completely in After Effects before attempting the key. If this had been a green screen instead of a blue screen, this wouldn't have shown as the green channel is full luma as well as the green color component... the blue channel is only 50% of the horizontal in resolution compared to the green and needs to be "blended" a bit.

I'll update the .png to reflect this. Thanks to David... both Raylight and CineForm should key equally well if observing this information...
 
Jim Arthurs said:
I'll update the .png to reflect this. Thanks to David... both Raylight and CineForm should key equally well if observing this information...
Click to expand...

I'd be interested to see that result because I strongly disagree.

The core reason is that the Raylight codec was designed from the ground up for quality, using the Avid codec as a benchmark. The Panasonic decoder (used by Cineform) was put together to make the P2 viewer work. I suspect it uses the hardware acceleration designed for DVD players. Your test image above reveals some of that. Here is another example (thanks to Barry Green for the source footage)

http://dvfilm.com/raylight/compare.gif

Look at the horizontal bar artifacts in the Panasonic image to the left of the frame.

The blockiness around the pupil in the Panasonic codec is due to the lack of chroma smoothing and is expected.
 
Marcus,

When Jim updates his PNG you will see the artifact he was showing is a 4:2:2 processing choice alone, and has little baring on the source decoder. There maybe quality differences in the implementation of DVCPRO-HD, we are happy to use any decoder available. If you make a DirectShow version of Raylight that outputs the source 4:2:2 YUV, that can plug straight into CineForm's conversion tools, without any changes to our code. If it proves to deliver greater quality DVCPRO-HD decoding we will be sure to promote it, and recommend it over the free version from Pansonic.
 
Last edited:
Hi all... David, it's Marcus, not Mario... :)

Anyway, the png is updated with CineForm with a slight blur on the blue channel only before pulling the matte... honestly, I see a bit more hair detail on the Cineform matte... in any event, knowing how the act of pulling a matte can mess with things, I've uploaded a layered photoshop file with the raw original conversions of the blue screen frame if anyone wants to experiment more. The Raylight version has black and white levels that differ from CineForm, but that's easy to correct for testing...

http://ftp.datausa.com/imageshoppe/outgoing/HVX_TESTS/STILLS/RAYLIGHT&CINEFORM_source.psd

In general, thanks to you both for supporting us PC users with nice options for the HVX...
 
You must log in or register to reply here.
Back
Top