Aliasing and Moire in fine details question(s)

[Antony Michael Wilson]

Hi Matt

What raster are you viewing at in the XF Utility? If it's not precisely 1920x1080, XF Utility is itself scaling the image and it's not going to do a good job!. It will introduce its own aliasing. XF Utility is in no way an appropriate way to judge aliasing. You need to view on a proper video monitor. A calibrated professional native 1080 display is best but a domestic 1080 TV will be a good start.

Lou, I've tested a lot on various monitors and with various charts and subjects. The bottom line is that you cannot entirely remove aliasing for a 1080i baseband viewing where there is motion on very fine detail. Detail at -7 or lower gets you close enough for most circumstances, though. The BBC settings are fine for a static zone plate test pattern but real life filming requires detail to be set at -7 or lower when shooting progressive. You don't need to go much lower than -3 shooting interlaced.

These cameras are very sharp indeed, so you do need to be extra careful with this issue, particularly if you need to keep SD deliverables in mind. I've had best results with SD down-converts keeping detail on acquisition at about -7 and then using AJA or Teranex hardware (not default settings) for the down-convert.

[Lou Bruno]

Thank you Mr. Wilson. I have noticed that even at -3 with an interlaced setting, fine details, such as tree branches produce the interline twitter. There is minimal, if any movement in the branches. Same goes for any striped patterns such as fabrics and even bricks. To address this issue, I have lowered the sharpening a bit on my HDTV as well as the -7 sharpening setting.


I guess we all agree that this is some sharp camera!

[Antony Michael Wilson]

To be honest, Lou, I have been doing nearly all of my testing shooting at 25P, so I defer to your experience shooting interlaced. My quick interlaced shooting test was nowhere near as thorough as progressive.

Of course, the aliasing/interline twitter I'm talking about is via a baseband 1080i output whether shot progressive or interlaced.

[Bill Weaver]

Originally Posted by Lou Bruno

Here we go MATT:


Sharpness Level: -7 or even -9

H Detail 8

HV Detail 2

Coring Level 5

Lower the sharpness on a HDTV as well.

Good luck.

worth a try -- but by doing this, are we subtracting from some of the image quality that attracted us to the camera in the first place?

[Bill Weaver]

Another thought --

I've been doing some test shooting, shoulder-held (so as to accent any potential aliasing problem), in 60P.

I haven't tried rendering to SD yet, but on playback on 720 HD TV and on 1080 res apple monitor, the is the most pleasing yet, with less aliasing, moire, etc.

Isn't this an alternative to cranking down the sharpness in the higher settings? HAs a nice, smooth, buttery look.

[Lou Bruno]

I never tried SD. I don't see the aliasing in HD that much defined on my PRO JVC HD studio monitor or even a VGA monitor. However, once rendered to a HD Blu-ray, I do see this sharpness on my HDTV. Perhaps it does smooth out due to less resolution in SD though.

On another note: This camera is so sharp that the -7 setting still produces a sharper image than my HVR-270 with the sharpen menu up to a +3.

[Antony Michael Wilson]

Originally Posted by Bill Weaver

worth a try -- but by doing this, are we subtracting from some of the image quality that attracted us to the camera in the first place?

No, not really. The sharpness of the XF300/305 out of the box is artificially enhanced (as is the case with nearly all cameras). Even with detail set to min (-10) you're still getting a very sharp, true HD image, as Alan Roberts says in his reports:

'Fig.1 shows a single quadrant of one pattern; for this exposure, the camera detail enhancement was turned down to minimum level (-10) which presumably means no correction, so this is probably the native performance of the camera. There are clearly no null zones, where the wanted lower frequencies mix with aliases produced by spectral folding of the unwanted higher frequencies, alias products. This is good evidence that the camera has 3 sensors of full 1920x1080 resolution, and that a “quarter-wave” filter (bi-refringent crystal or other fabricated filter) has been included in the optical path, and is well suited to the camera’s resolution.
There was no evidence of aliasing caused by out-of- band frequencies in the coloured zone-plate patterns. Usable resolution up to about 900 lines vertically and 1800 horizontally is clear. Also, there was no evidence through aliasing that “precision offset” (the spatial offsetting of the green sensor from red and blue by exactly 1⁄2 pixel spacing to improve luma resolution) is used in this camera.
It is rare to see resolution so clearly as this, which is very encouraging.'

I would suggest that it is a good idea to set detail to min/off and dial it back in to taste.

[Jerry Laurence]

I am awaiting delivery of my XF-300 and therefore extremely interested in these posts. Looking at Alan Robert's report, as well as all these posts, it seems that much could be done just by adding more noise reduction, which reduces sharpness to acceptable levels anyway. Wouldn't this control alone reduce unwanted aliasing and noise at the same time?

[Antony Michael Wilson]

Yes, NR will reduce aliasing but it's a bit of a blunt instrument, to be honest. We tested all this quite thoroughly and in order to reduce aliasing in fine detail with NR resolution takes a big hit. It's much better to reduce sharpening since the underlying (un-sharpened) image is plenty sharp enough - if that makes any sense!

It's also important to remember that NR doesn't just reduce effective resolution, it also introduces many other artefacts, so is best avoided where possible. Careful, gentle approach is necessary with all forms of DNR - even the best algorithms. Certain other cameras suffer because NR cannot be reduced or disabled. The XF300/305 is a well engineered camera, so you can control and disable NR. Also, the automatic NR is pretty good and is on the gentle side, so I would leave it off or on automatic unless there are real issues with noise and/or aliasing on specific occasions/shots.

[Matt Ford]

Originally Posted by Antony Michael Wilson

Hi Matt

What raster are you viewing at in the XF Utility? If it's not precisely 1920x1080, XF Utility is itself scaling the image and it's not going to do a good job!. It will introduce its own aliasing. XF Utility is in no way an appropriate way to judge aliasing. You need to view on a proper video monitor. A calibrated professional native 1080 display is best but a domestic 1080 TV will be a good start.

Lou, I've tested a lot on various monitors and with various charts and subjects. The bottom line is that you cannot entirely remove aliasing for a 1080i baseband viewing where there is motion on very fine detail. Detail at -7 or lower gets you close enough for most circumstances, though. The BBC settings are fine for a static zone plate test pattern but real life filming requires detail to be set at -7 or lower when shooting progressive. You don't need to go much lower than -3 shooting interlaced.

These cameras are very sharp indeed, so you do need to be extra careful with this issue, particularly if you need to keep SD deliverables in mind. I've had best results with SD down-converts keeping detail on acquisition at about -7 and then using AJA or Teranex hardware (not default settings) for the down-convert.

Thanks Antony

Screen res on the macbook pro is only 1440 by 900, That could be it!

This is excellent info and Im sure helpful to all.

So it appears that turning down the sharpness to -3 and more is the way to go for real life use.
So what about the other settings? Im trying Bruno's out but will not have access to a decent screen until I return to the UK on the 28th. How are you setting you detail, I note your recommendation to turn it right down, do you mean both? and coring? Would I be right in presuming that this will help with gain noise, smooth it out slightly?

Its good to be approaching the best CP settings.

Matt

[Bill Weaver]

I did a test shoot in a local cemetery (apple blossoms, bare trees, grass, rugged stone, etc) in 30p, with the BBC settings modified further with sharpness to -7 and coring at 5, etc.

Then, I went to DVD with the test footage via Ken Stone's formula (except that I started with native timeline - XDCam HD 8 50mps 422.)

Exporting HDV Video from the Timeline to Standard Definition DVD

Really good results. Wide shots were a bit mushy as one would expect with so much challenging subject matter, but overall the footage was stunning on my 42" 720 HDTV.

This has been a great thread with a lot of useful info.

Would it make sense to start a general XF thread on post production, deliverables, etc, where we could keep editing, grading, etc, issues within our realm? Just a thought. And thanks again everyone, for all the excellent information and perspectives!