Mac Musings

Resolution Independent Display

- 1998.12.30 - Tip Jar

Thanks to utilities like SmoothType, ATM, and the anti-aliasing built into Mac OS 8.5, type today can look better on the screen than ever before. For instance, in the black and white sample to the right, anti-aliasing (courtesy of PhotoShop) uses shaded pixels in spots where neither black nor white best fits the character.

This is a big improvement from the days of 1-bit displays and less smooth type.

However, it doesn't solve all our problems, as users of the PowerBook G3 with its 1024 x 768 screen have discovered. Anti-aliasing does a wonderful job at 1024 x 768 resolution, but when emulating 800 x 600 or 640 x 480 (see image to right), the combination of anti-aliasing and scaling the image to screen resolution gets, to say the least, fuzzy.

In my previous column, Changing PC Paradigms, I speculated how a 1920 x 1440 screen, by offering three times as many pixels vertically and horizontally (compared with 640 x 480), could provide a remarkably sharp image. But using simple scaling technology to remap 640 x 480 to the larger screen would result in something like this:

Granted, it would be a lot smaller than it appears here, so it would look better than this, but it would still a lot of fuzzy text - just smaller fuzzy text.

What if that high resolution screen didn't simply remap pixels, but actually drew the characters using all those extra pixels?* QuickDraw already has the capability to do this, as shown by displaying text and graphics at 72 dots per inch on the screen while printing them at 144 dpi on an ImageWriter, 300 dpi on an older LaserWriter, and 1440 x 720 dpi on an Epson Stylus, just to give a few examples.

Using all those extra pixels, the above text would look this clear:

Again, at the higher resolution of today's LCDs (IBM has achieved 150 ppi and is working toward 200 ppi), this would look incredibly sharp - far better than the scaling Apple currently achieves when displaying lower screen settings on a higher resolution screen.

This could give Apple a real visual edge in the laptop market, one place where the PowerBook line already shines. It would surpass Microsoft's ClearType technology (based on an expired Apple patent), although there's no reason Apple couldn't incorporate that idea as well.

Since QuickDraw already has the capability to do this, we can hope Apple will include resolution independent display on future PowerBooks, building the necessary hooks into ROM or the Mac OS so programmers can readily work with the technology. (And, of course, doing the same for the next generation of LCD monitors.)


Doug responded to Changing PC Paradigms, writing,

"This is actually the original intent of QuickDraw.

"The BitMap/PixMap data structures, which are the heart of QuickDraw, have horizontal and vertical dpi [dots per inch] fields. They also have a lot of other fields which were intended to be more general than it actually turned out. These resolution fields are actually looked at when QuickDraw renders output to a printer. "The problem is that on the display side everyone took for granted that 72 ppi is the resolution - and that assumption metastasized throughout the entire GUI.

"DisplayPostscript is obviously resolution independent, as QuickDraw was intended to be.

"DisplayPostscript is dead, but functionally PDF succeeds it and it is also resolution independent. It would be a nightmare to restore QuickDraw to its resolution independent roots, but perhaps this will occur as part of the adoption of PDF as the metafile format for Mac OS X. CopyBits comes to mind as one of the biggest offenders. Then of course, all the GUI code which skirts QuickDraw will have to be excised. Legacy apps will look/behave oddly, although it could be stipulated that all Blue Box apps behaved as before."

* Editor's note: This is exactly what Apple did in 2010 when it introduced the iPhone 4 and its "Retina" display.

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Dan Knight has been using Macs since 1986, sold Macs for several years, supported them for many more years, and has been publishing Low End Mac since April 1997. If you find Dan's articles helpful, please consider making a donation to his tip jar.

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