Strobing/flashing socks - Help

[Travis Wheaton]

G'day,

I have just burnt a test run of my showcase DVD, and discovered that a pair of black and white socks, and a grill at the bottom of a refrigerator are both strobing/flashing in one of the films.

When viewing the DV movie file on my computer, or via AppleTV, it looks fine, but once it's been through DVD Studio Pro (4) and converted to VOB for the DVD, the two things strobe quite noticeably.

Should I be looking at increasing the settings in DVD Studio... or should this be corrected via flicker filter (?) in Final Cut Pro (5.1)?

Thanks


Travis

[Travis Wheaton]

Am I using the wrong terminology?

[Geoffrey Cox]

No, I think you make things clear, it's just one of those very annoying issues that could be caused by so many things - I've certainly had it and not always solved it, it even varying depending on the TV. Is it interlaced material? De-interlacing that clip might help. You could give more detail - it might help with the responses.

[Les Wilson]

It sounds like Moire. It's something that happens for various reasons one of which is shooting certain small patterns at certain angles and focal length in an interlaced format such as DV. Deinterlace the material as early in the workflow as possible as already suggested.

[Travis Wheaton]

Revisiting this issue, as I'm sending my DVD off for a job as a tech officer, so better look like I know what I'm doing...

The footage was recorded as 1080p25 on a Sony XDCam... When it was captured to hard drive using (a Sony app?), it has come over as 1440x1080p25... rather than 1920x1080p25... (I've seen talk of this issue around the web... not sure if we had the camera set to record in this reduced setting or if it was the software when doing the import...)

I don't have the original footage - only the 1440 files.

As that ratio looks wrong (ie not quite widescreen, nor 4:3), I had set my sequence as "HDTV 1080i (16:9)", as it was the only 1080 preset listed (FCP5.1)... and the footage was destined for DVD anyway... (which I was thinking was an interlaced format...?) I then used "distort" in the Motion tab to "stretch" the 1440 footage to the 1920 width... (And frankly, it doesn't look stretched at all to my eyes)

Should I have chosen a different setting for the Sequence? Which one? Is there a better way to adjust the 1440 ratio?

As to the socks... I tried reducing the white levels (someone elsewhere suggested "knocking out the luma")... this didn't help sadly...


Thankyou

[Geoffrey Cox]

Travis I always let FCP set the sequence settings itself by dragging a file into the timeline of a fresh session - it then asks you if you want to adjust the settings to match the clip to which you say yes. This has always worked for me.

1440 x 1080 will provide the same size as 1920 x 1080 as in the former the pixels are rectangular rather than square, so there is no reason to distort the images. Cheaper cameras use 1440 to save on resolution.

DVD is an interlaced medium but if you search this forum you will find discussion on this with people with far more technical knowledge than me explaining it is not quite as simple as that. Either way I always use interlaced material for DVD without de-ionterlacing and it looks great. Occasionally i find clips with very fast motion or strangely, stills, do need de-interlacing for some reason but I process these separately and bring them back into the timeline before mastering for DVD. Mind you if you have 25p footage why are you worrying about interlacing? FCP should have a 108025p setting unless your version is too old (FCP6 has it).

[Eric Olson]

Originally Posted by Travis Wheaton

a pair of black and white socks, and a grill at the bottom of a refrigerator are both strobing/flashing in one of the films.

This sounds like aliasing produced when your HD source is converted to SD resolution for the DVD. Scaling routines that avoid aliasing are computationally expensive, so many NLEs choose simpler algorithms. The typical work around is to blur the original HD source before it is down converted. The blur will make the original HD footage look blurry, but after that footage is scaled down to DVD resolution it will look sharp again and the flashing should be gone. Note that it may take some experimentation to find the correct level of blur. I would first try a 2x2 or 3x3 box blur because it is simple and fast.

[Travis Wheaton]

Originally Posted by Geoffrey Cox

Travis I always let FCP set the sequence settings itself by dragging a file into the timeline of a fresh session - it then asks you if you want to adjust the settings to match the clip to which you say yes. This has always worked for me.

1440 x 1080 will provide the same size as 1920 x 1080 as in the former the pixels are rectangular rather than square, so there is no reason to distort the images. Cheaper cameras use 1440 to save on resolution.

Aha.... 1440 is a pixel ratio thing! I'd read various other queries regarding this issue... mostly people scratching their heads thinking they'd done something wrong somewhere.

(runs away and plays around in Final Cut...)

I see... I just tried changing the Sequence to the "HD 1440 x 1080 16:9" setting, with "HD 1440 x 1080" for the pixel aspect ratio... When I dragged some raw footage to this sequence, it defaulted the "Aspect Ratio" in the Motion tab to 33.333... which gave a 4:3 looking image with black bars on either side, however by changing the ratio to 0, it filled the screen properly. Comparing the two images - my 1920x1080 with distorted corners, and this 1440x1080 "natural" approach - they produce the same image... however Final Cut needed to render my method, so I know which one my uni tutor would tell me to use...

Thanks!

Originally Posted by Geoffrey Cox

DVD is an interlaced medium but if you search this forum you will find discussion on this with people with far more technical knowledge than me explaining it is not quite as simple as that. Either way I always use interlaced material for DVD without de-ionterlacing and it looks great. Occasionally i find clips with very fast motion or strangely, stills, do need de-interlacing for some reason but I process these separately and bring them back into the timeline before mastering for DVD. Mind you if you have 25p footage why are you worrying about interlacing? FCP should have a 108025p setting unless your version is too old (FCP6 has it).

My version of FCP (5.1 - yep, old...) doesn't have a 1920x1080p25 Sequence frame size option... I will now use the 1440x1080 setting anyway, so hopefully wont be an issue now....

ALTHOUGH - I have a Panasonic TM900, which records 1920x1080p50, for which there is no setting for in my Final Cut.... only the HD 1080i...

Maybe an upgrade really is becoming an issue...

Originally Posted by Eric Olson

This sounds like aliasing produced when your HD source is converted to SD resolution for the DVD. Scaling routines that avoid aliasing are computationally expensive, so many NLEs choose simpler algorithms. The typical work around is to blur the original HD source before it is down converted. The blur will make the original HD footage look blurry, but after that footage is scaled down to DVD resolution it will look sharp again and the flashing should be gone. Note that it may take some experimentation to find the correct level of blur. I would first try a 2x2 or 3x3 box blur because it is simple and fast.

I found a blur filter to try out... Will give it a go.

[Travis Wheaton]

Not sure if it's what you had in mind, but I used a gaussian blur, set to luminance, radius 2, and it worked.

No real loss of picture quality, but loss of the strobing.

Just used it again for a video of a weekend trip to the snow... stark trees against a snowy backdrop, and a grille on the back of the snow-machine, both caused strobing, which I could fix the same way.

Thank-you.