Overview
Until High Definition Television (HDTV) arrives, we must use the National Television Standard Committee (NTSC) video standard. This 40-year old standard, designed for transmission of color video camera images over a small bandwidth, is not well suited for the sharp, full-color images that today's computers are capable of producing. Video professionals, when working with computer graphic (CG) images, use two monitors: a computer monitor for producing CGs and a NTSC monitor to view how a CG will look on video.
Following these guidelines and tips will enable you to create the finest quality images and animations that will reproduce best on videotape.
Guidelines
Avoid thin, single-scanline horizontal lines and dots
Due to the interlacing of a video image, fine lines will flicker and produce visually annoying displays. You can either smooth out the fine line by blurring it, or you can simply add an identical line directly above or below the first.
Avoid Chroma Crawl
Chroma crawl is a region between two colors creating a border of creeping colored lines. This can make text almost unreadable. The solution is to choose different neighboring colors. Hints: Avoid red backgrounds or letters combined with solid green or blue colors. For text, the safest color combinations is white letters on a BLUE background. White against a black background can cause buzzing in the audio. Pastel letters on a black or dark-gray background may also be acceptable. The more saturated colors you add to the image, the more you risk chroma crawl.
Plan for Surprising Color Changes From Your Computer Monitor to the Video Monitor
Certain colors on your high-quality RGB monitor look entirely different when viewed on a video monitor in NTSC since colors are not distributed evenly within the NTSC frequency band. For example, human vision tends to be more sensitive to skin tones and the green spectrum. The NTSC video signal is deliberately biased on the color green, less on red, and even less on blue.
Avoid Highly Saturated Colors
No way around it, the NTSC video standard does not support highly saturated colors. In fact, the FCC established laws regarding out-of-range colors in video broadcasts. Deep rich colors which are delightful in film or print are off limits in NTSC. In video, saturated blues and reds turn to pastels. Yellow drifts towards white when overly saturated. In fact, red tends to go outside limits very quickly and can overdrive NTSC monitor drivers resulting in an ugly black patch. Some professional paint applications offer ways of indicating or avoiding these colors. If your application does not offer this feature but uses a Hue, Saturation, Value color model, then set the saturation to less than 70%.
Orient Primary Graphics Content in the Center of the Screen
Viewers are used to seeing the action in the center of their screen. Artistic license and creativity may be nice, but off-center messages may be missed, so here it's best not to fight human nature. Place important text in the center, and long messages over several screens.
Keep Within the Safe Titling Area
The Safe Titling Area (S.T.A.) is the region that is 80% inside the viewable screen area. Common television sets cut up to 20% of the picture off the sides. While computer monitors show every pixel, this is not so on TVs. Text outside the S.T.A. will be overscanned, cutoff and become unreadable.
Avoid Finely Detailed Grids
Grids of horizontal or vertical high-contrasting lines will create a beautiful, but undesirable, rainbow pattern. This happens because the video color processors mix some of the color signal with some of the black-and-white component in the fine lines, resulting in false color artifacts. A remedy is to smooth lines with blurring or widening.
Make Your Text Large
The text on your master video tape may be sharp and clear, but after duplication, transmission, and processing, colors become blurred and distorted, noise increases, and fine letters become illegible. Make the text large enough to account for the degradation of the video signal. Remember, for the most part, it's still an analog world out there, so your images will be degraded. Also, typically, viewers sit ten to twenty feet back from a TV screen, so make your text readable from the back of the room.
Know the Aspect Ratio You Are Using
NTSC has a 4:3 aspect ratio, your computer screen is something else, so converting screen video to NTSC is not 1:1. Either a region of the screen is converted one-for-one to NTSC, or the screen is pixel-averaged to the NTSC resolution. Test your computer's video scan converter to see how square objects are output. Depending on your system, they may appear rectangular. Also, video hardware and software use various image sizes. An image created with a 640 x 480 resolution, when transferred to a 720 x 486 system may result in elongated objects. There are professional applications which convert aspect ratios, resolutions, color depth and file types to their own internal values. You need to conform to a single aspect ratio especially when combining and compositing images from varying sources.
Calibrate and Care For Your System
Calibration is very important so you won't be unpleasantly surprised when you show your video on a different system. You must remain within the NTSC illuminance and chroma specifications. Don't trust your eye for color calibration. My first video looked great on my monitor, but when I took it to a calibrated studio, all my images were slightly green. The timing of the sync pulse and burst pulse must be within 3ns of FCC specifications. Nonstandard sync timing will cause your image to be shifted to the left or right. An out of phase burst pulse will cause a color shift. Once your system is calibrated, tape over the controls so they don't get changed, and periodically recheck the calibration of your system.
Keep the heads of your VCR clean. Dirt will cause video static. If you are not a competent video technician, don't clean the heads yourself. Video heads are very, VERY brittle and can EASILY be damaged. Replacing heads on any VCR is expensive. Don't kink or step on your coaxial cables, this will change the bandwidth characteristics at the least, or at worst break the inner center conductor.
Render to NTSC Resolution
Most likely, the resolution of your computer screen is much better than NTSC. For video, render images to NTSC resolution to save rendering time and memory space. Details at resolutions greater than NTSC will not be seen, and unfiltered high frequency energy can produce unwanted color artifacts. Computer video frame buffers vary in size between 512x480 to 720x486, so know the resolution of your buffer and render to that size.
Compress Sparingly and Avoid Generation Loss
Because of space restrictions or hardware limitations, raster images are often compressed. Most compression schemes designed for video are lossy and produce image artifacts. For best results, avoid using compression. If your system is unable to record non-compressed images, you may wish to transfer your images to the LC Video Production Laboratory for recording (see LC Video Tape Output Services for more information). If you do use compression, use it sparingly. Compression ratios of 4:1 are near studio-quality, and 20:1 is VHS quality. Greater compression will result in poor image quality.
Avoiding generation loss is especially important with compressed images. Each generation of uncompressing and recompressing multiplies image artifacts, resulting in increasingly poor quality images.
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