Powerbook 540c LCD, Can It Run In Grayscale Mode?

I reinstalled the 540 panel in the 520, and in Control Panel > Monitor > Options it actually says "640x480, 64 grays" so that footnote on the specifications page is correct. Apparently the LCD in the 540 is a true 6-bit panel.

What does it say under Control Panel > Monitor > Options for the 540c?

Interesting thought. I wonder if the "driver" side of things could be taken care of in one of the FPGA/CPLD based panel driver boards from Chinese ebay sellers.

Click to expand...

The "Driver" issues would actually be OS and application related. Let's say that you were to, via whatever method, modify a video card so it supported something ridonkulous like 24 bit grayscale. (Most accurate way I can think of, assuming we're going oldschool and trying to do this with an analog monitor output, would be to make a board that had three very-high-speed 8 bit analog-to-digital converters on one side and a single 24 bit DAC on the other, connected to the single input on a true monochrome monitor. Digitize the incoming RGB signals into three bytes of data, stack them up, and use that on the output side as a single 24 bit value. Easy Peasy, relatively, The simplest method would be to simply use a different value resistor on each RGB line to combine them into one signal; see the comment below as to why from a practical standpoint the results would probably be indistinguishable.) The problem now is that you'll have to describe to the OS that it should treat its 24 bit framebuffer as grayscale, IE, use the three bytes that were RGB into a linear set of luminosity values instead of three sets of luminosity+chroma; if you simply keep working with 24 bit images as 24 bit color you might be able to display some pretty pictures but they won't make a lick of sense if you view them on a normal machine. "Deep Color" support (IE, support for 30/36/48 bit color depths) has been in Windows for a few years but googling seems to indicate it's *not* really in OS X yet. (Oddly there *was* apparently a 30 bit deep color card made by Radius for Macs in the 90's that was supported by PhotoShop.). I have no idea if "Deep Color" support comes along with an understanding of extended grayscale only images, but it would seem to be a prerequisite for really making use of a deeper grayscale framebuffer.

Of course, one thing to think about is if you were doing this analog is the peak-to-peak voltage swing for a VGA (color or grayscale) monitor is only 0.7 volts. Even at 10-bit resolution the difference between two adjacently-shaded grayscale pixels is probably less than the voltage swings you'd get in the cable from, say, ripple from nearby AC feeds or the computer's power supply. 16 or 24 bit would be ludicrous overkill.

Apparently the LCD in the 540 is a true 6-bit panel.

Click to expand...

That doesn't actually surprise me. 6 bit grey resolution was what Mono VGA was capable of, it would make sense they'd manufacture panels that support it.

I'm sure with the color display the control panel says "256 greys". I would just wager that in practice they're dithered, not true.

Apparently the LCD in the 540 is a true 6-bit panel.

Click to expand...

That doesn't actually surprise me. 6 bit grey resolution was what Mono VGA was capable of, it would make sense they'd manufacture panels that support it.

I'm sure with the color display the control panel says "256 greys". I would just wager that in practice they're dithered, not true.

Click to expand...

What's interesting about this is that it means that the CLUT register is capable of either 256 colors (3.3.2.0.0), or, at a minimum, a 6-bit linear grayscale value (6.0.0). Considering grayscale values larger than a single color channel are possible in the register, technically, it should be possible for it to output true 256 grayscale values, with a true 8-bit grayscale panel attached to it. Of course, at that time, the most one ever saw was 6-bit panels. However, it would be fun to find a true 8-bit grayscale panel and see if the CLUT could drive it at the full 8-bit range. The OS is capable of handling 256 grays, so I don't see why not. A fun little hack to try. Unfortunately, far beyond my capabilities.

Testing the Toshiba panel for the 540c in Grayscale mode, it can display 27 distinct shades (Black, White & 25 shades of gray inbetween). This means it should be capable of displaying 19683 colors @ 640x400. So, Apple's estimate of 24000 isn't too far off. Since it can clearly display more than 16 shades, it must be a 15-bit panel. Really quite good for that time period.

So, the 540 panel is indeed superior to the color panels in displaying grayscale, since it is capable true 64 grayscale. However, this makes the 540c superior to any of the 4-bit grayscale panels.

Unfortunately, the 540 panels suffer from terminal tunnel vision, as do all grayscale active matrix panels of that time period.

I'd be interested in someone with a Sharp 540c panel testing the grayscale gradients in grayscale mode. Since the colors on the Sharp panel appear more vibrant, I expect it is capable of displaying the full 32 shades of gray.

It would be fantastic if mcdermd could do this quick test because I know for sure he has 540c's with both Tosh and Sharp Panels.

So maybe the people that purchased the 540 over the 540c might not been all about $$ savings, maybe they might of needed that screen for some B&W Desktop Publishing? Maybe the 540 was more expensive then that 540c< at the time?

If it can do 32 shades, that would mean the Toshiba can display less colors, but has a finer dot pitch, whereas the Sharp can display more colors, but has a more coarse dot pitch.

Personally, I'd go for dot pitch. A coarse dot pitch drives me nuts.

There's also other one other reason - power efficiency. With a greyscale active matrix display, sitting outside, you can turn the backlight all the way off and still see what you're doing. Not quite the case with a colour display, or a passive matrix.