View Full Version : Digital signal to Analog signal : Alot of jitters
02 February 2005, 06:30 AM
Has anyone had the problem of having 3D footage that has been totally comped, looks fine on a computer monitor, but then you view it on an analog source through a Broadcast monitor, and it is extremely flickery with alot of banding?
The footage in question has alot high frequency textures in it (extreme closeups of concrete), but if it looks fine on a computer monitor then it should look fine on a TV right (obviously not including colours etc). Do I need some sort of anti-aliasing filter? Not sure what the solution is.
I have even burnt the footage to DVD and the problem occurs (when I view the burnt DVD footage on my DVD player on my computer monitor, the footage jitters alot, but if i view the frames through a compositing program, they are fine.) Something happens when the footage is prepared for TV, and i dont know what.
Any help would be greatly appreciated.
02 February 2005, 01:27 PM
What frame rate are you rendering at? If you have a composition program you could try and do a horizontal blur of about 1 or 2. Not sure as to why it doing that, most likely the textures. what is the resolution of the textures?
02 February 2005, 03:27 PM
This may be helpful to you -
The luma range for NTSC video is 16-235, while in computer graphics the RGB range is 0-255. Before you create 3D files or graphics, adjust the output levels of your file to 16 and 235.
As with the luma values, all color values should be within 16-235, with black being 16,16,16 and white 235,235,235. However, you should stay away from using saturated colors, which tend to bleed even if they are within the legal range. A rule of thumb is to not use values higher than 180 for colors. Also, be very careful when using red. Even with values a bit lower than 180 you still might see some bleeding with red. As stated above, these colors will look darker than the colors you are usually accustomed to working with in graphics, but on video they will look better.
Graphics programs often have filters that allow only NTSC-safe colors, but these vary in quality. Some might permit some illegal colors to sneak through, while others, like the one in most Adobe products, can be too aggressive and reduce your color too much. For the most control and best results, it's best to take note of the colors you're using yourself.
Lines and Edges
Avoid using thin horizontal lines, which can flicker or "twitter" due to video's interlacing. Lines should be at least two pixels high, although preferably larger than that. Also avoid using serifed fonts, unless they are large or bold (in fact, any fonts you use should be large and bold, since small fonts may become unreadable on a television.)
Overly sharp edges can cause a problem for video as well. Since a scan line in video is represented by an analog waveform, it cannot instantaneously change from white to black; it needs some room to "ramp." When video attempts this instant change, it often overshoots, creating a ringing effect around the edge or causing the image to pulsate. Overly sharp edges can also create mosquito noise artifacts when compressed to DV or MPEG-2 or, in extreme cases when they are combined with illegal colors, the overmodulated picture signal leaks into the sound subcarrier and causes a buzzing noise.
The solution to the issue of overly sharp edges is to add a gaussian blur of between 0.2-1.0 pixels. The will have the effect of antialiasing the image and eliminating the hard edges. I know it seems counter-intuitive to be blurring your images to make them look better, but pretty much nothing about NTSC is intuitive.
02 February 2005, 05:11 PM
Ahhh.... the wonders of NTSC.....
A friend of mine who works at the BBC tells me that they call it "Never Twice the Same Colour"
(that said, what Cathy said holds true for PAL too.... PAL's just a lot more reliable when it comes to colour reproduction....)
02 February 2005, 04:25 AM
some 3d programs offer settings for anti aliasing. you may loose some of your detail, but you may have to smooth out the 3d images to keep them from looking weird on TV. I know 3ds MAX has a VIDEO setting that really smooths out an image, or you can apply blurs in your compositing software.
but don't worry about it to much, most TV are going to throw away all your hard work anyway. that's why they are cheap compared to a computer montor, your NTSC TV is only 720x486 and you may be lucky to get 400 lines out from a good DVD player. Whiel your monitor, well geeze, they can go up to 1600x1200 or more now a days.
I know when I match live action with CG, I have to really blur up the CG to make it fit into DV compressed footage.
ALWAYS CHECK YOUR STUFF ON A TV BEFORE RENDERING IT ALL OUT.
can't stress that enough. even if it cost you some extra time, render out just that material on a flat object, or a sphere, pump it out to a TV and see if the texture works. it's a whole lot better than blowing hours on rendering a sequence just to find one map that twitches like a possum stuck on a power line.
02 February 2005, 12:08 AM
Thanks for the replies everyone.
The directional blur did solve the problem in that it effectively "anti-aliased" the image. However it does seem extremely counter intuitive.
We are using PAL, however alot of the rules do apply for both NTSC and PAL as Hugh said.
Thanks again guys.
02 February 2006, 01:15 AM
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