mkb@ROVER.RI.CMU.EDU (Mike Blackwell) (02/20/88)
Since a couple of people have asked about interlaced video, here's a brief explanation: By default, the Mac II video card puts out separate red, green and blue channels, non-interaced at 67Hz (meaning every scan line is drawn each frame, and a full frame is drawn 67 times per second). This is why the image on the Apple color monitor is so crisp. What the init does is reprogram the video card to output the same R, G and B signals, but interlaced, so during one frame time all of the even scan lines are drawn and during the next the odd scan lines are drawn. This lowers the effective bandwidth of the signal to 33.5 Hz, allowing you to use a cheaper monitor (televisions use this trick). Thus, using this init, you can use any random analog RGB display (such as you can pick up cheaply for an IBM-PC, etc), but the results won't be so clean and crisp (there'll be noticible flicker on things like small text and single pixel wide horizontal lines). You'd probably not want to use this as your main monitor, but it makes a good cost effective second monitor for displaying color pictures, like with Vision Lab. Note that this interlace mode is NOT the same thing as NTSC. In NTSC (for Never Twice the Same Color...), all three colors are encoded onto one channel (further reducing the picture quality along the way). As far as I know, the Mac video card can't be programmed to do this, and you'd probably never want to, anyway. The INIT I posted is just a quick hack... It doesn't do things like check to make sure you're really on a Mac II, and there is really a video card in the selected slot, so it will probably crash if installed on a Mac configured differently than what it expects. It should also grab the slot number out of a resource, so you could configure it with ResEdit, instead of having to recompile. But I included the source code... please feel free to imbelish... Mike Blackwell mkb@rover.ri.cmu.edu Carnegie-Mellon University Pittsburgh, PA, 15213 412-268-8830