Overall Functional Description
The VHD-4403 ULTRA’s purpose is twofold. First, it provides aspect ratio control and can do so on either a WIDESCREEN or a standard 4:3 screen. Second, it pro- vides a clean, progressive signal to the projector.
The processing the VHD-4403 ULTRA uses is called SCALING. Scaling is simply a way of taking a signal, ‘digitizing’ it, then converting it to any of a number of resolu- tions. It is by manipulating the algorithms of the scaling process that we are able to not only produce properly-configured aspect ratios, but to provide the most effective scan rate for the projector it will be used with.
An INTERLACED signal is the type of signal that comes from all consumer sources (with the exception of DTV decoders and computers). DVD players, Laser Disc players, and VCRs are all examples of source equipment that have interlaced out- puts. An interlaced signal is simply described as this:
240 lines (odd) | 240 lines (even) |
First 1/60th of a second | Second 1/60th of a second |
An NTSC picture is made of approximately 480 lines. Images are drawn 60 times a sec- ond, but in an interlaced system, only half the lines are drawn each ‘pass’. Therefore, it takes two ‘passes’ to actually complete the picture. On the first 1/60th of a second, all of the ‘ODD’ lines are drawn, then the ‘EVEN’ lines the next 1/60th of a second. This is also called ‘480i’, where 480 is the total number of lines of resolution, and ‘i’ means interlaced.
A PROGRESSIVE signal, however, draws all 480 lines each 1/60th of a second, not half and half like an interlaced signal. A ‘line doubler’, for example, outputs a 480-line progressive signal (also known as 480P). The line doubler takes the first field (odd lines), and stores them in memory, then takes the second field (even lines) and does the same. Then, all 480 are output at once, and then the same frame is repeated.
The VHD-4403 ULTRA starts off as a line doubler by ‘de-interlacing’ the signal. Then, the 480p signal is scaled to appropriate resolution, and then output to the pro- jector. It is Runco’s high-quality scaling process as well as its de-interlacing that pro- vides the clean, resolved image that you see from your VX projector. It is also how the processor can provide aspect ratio control.
In the next chapter, the individual menu items will be described in detail. Overall, the VHD-4403 ULTRA has a number of useful functions aside from the scaling and de- interlacing described above. It has typical picture controls, including COLOR (satura- tion), TINT (hue), BRIGHTNESS (black level), SHARPNESS, CONTRAST (ratio of white to black) and other picture enhancements such as LUMA and CHROMA ENHANCE.
