External LCD monitors with DVI PowerBook: Banding Issues

Question

I have a DVI PB and would like to attach an external LCD monitor. I've looked at both Samsung 20 inch and ViewSonic 19 inch versions but whenever I attach them, I get "banding" around the edges of the external monitor. Tonight, I went to CompUSA to look at the Samsung 204B 20 inch. Taking my PB with me, I hooked up and set the resolution to 1600 x 1200 and the Samsung had huge, fat black banding all around the monitor. If you don't know - banding looks like a large, black border going around the screen. The sales guy pushed some auto-set buttons (which is said always work to remove the banding) but it didn't fix the issue. Any suggestions? Is there some secret that I'm not aware of on how to attach and use an external LCD monitor with the PB? One note: I did set the resolution down to 1280 x 1024, which worked fine to remove the banding but it monitor looked horrible. Not the best resolution for a large monitor.
Thanks,
B. Rose
TiBook 800 & iBook SE   Mac OS X (10.4.6)  

Answer 1

Hi, Bill. I can't speak to whatever happened with the Viewsonic monitor, since you didn't tell us about that, but it sounds as though the Samsung was in display mirroring mode rather than extended-desktop mode. The F7 key on your Powerbook's keyboard toggles an external monitor between the two modes. In mirror mode, the external monitor displays exactly the same thing as the built-in display. In extended-desktop mode, it functions as a separate portion of your desktop, and you can drag things (windows, icons) from one monitor onto the other. If you're going to use both displays, extended-desktop mode is probably what you'll want: why keep two copies of the same thing in front of you?
In mirrored mode, the fact that your Powerbook's display has a maximum resolution of 1280 x 854 means that only 1280 x 854 pixels of the external monitor can be used — leaving wide black borders of untapped pixels around the copy of your PB's display that's centered on the external monitor. In extended-desktop mode, the external display's native resolution of 1600 x 1200 can all be used, provided that your 32MB of VRAM is sufficient to drive the total of (1280 x 854) + (1600 x 1200) = 3,013,120 pixels, at the bit depth you've selected. (You might have to use the extended-desktop mode in Thousands of colors, rather than Millions.)
Another issue that comes into play with display mirroring is that the 4:3 aspect ratio of the 1600 x 1200 Samsung is different from the 3:2 aspect ratio of the Powerbook's display. If you set the Samsung's resolution to 1280 x 1024 to match the pixel width of the PB display, the top and bottom of the Samsung will be black bands, because the PB isn't manufacturing any pixels to fill those bands. And it will be blurry, because the Samsung has to interpolate to make 1600 pixels look (sort of) like 1280 pixels. Unlike a CRT display, the actual number of pixels in an LCD is fixed. When you change resolution settings on an LCD from its native (maximum) resolution to anything less, the image is always blurred. Only the native resolution can be really sharp.