CRT Screen Size, Resolution, and Sharpness

I have yet to see a 15″ CRT monitor that looks crisp at 1024 x 768, or even a 19″ one that does justice to 1280 x 960 or 1280 x 1024 resolution. Yet these monitors are often rated for these settings, and often even higher ones.

What’s going on here?

Quite simply, we’re looking at the difference between how many dots per inch the computer is trying to display and how many dots per inch the monitor can show before they start running into each other.

A decent monitor today [1999] will have a horizontal dot pitch of about 0.22 mm. That is about 4.5 dots per millimeter or 115 dots per inch. Anything higher than that will be fuzzy, since the monitor will be trying to display more than one pixel per screen dot.monitor (For more on dot pitch, see Monitor Dot Pitch.)

My 19″ Optiquest V95 monitor has an image about 13.5″ wide, so it should be able to crisply display 1550 pixels at one per dot. Yet if I set it to 1600×1024, it’s fuzzy. And even if step back to 1280 x 960 or 1280 x 1024, it’s still fuzzy. But 1152 x 870 seems crisp.

Weird, isn’t it.

Obviously, there’s more to crisp display than simple dot pitch and resolution would indicate. That doesn’t mean that dot pitch isn’t a good indicator of screen sharpness, only that it doesn’t directly predict the maximum crisp display setting.

In reality, you have to be at 1-1/3 to 1-1/2 dots per pixel before the screen looks pretty sharp. In the case of my Optiquest, that explains why 1280 dots horizontally doesn’t quite cut it, but 1152 works very nicely.

Looking at another example, while my 17″ Nokia 447z was in the shop (now for the third time) and before I picked up the Optiquest, I used a 15″ Compaq Presario v410 monitor. It claimed to support some high resolutions, but the highest one that looked good was 832 x 624.

The Presario has a dot pitch of 0.28, which comes to about 0.22 horizontally. It can display a fuzzy 1024 x 768. Again, a 10.5″ horizontal dimension predicts a sharp 1200 dots, but it just doesn’t work out in the real world.

Instead, we seem to be at that ratio of about 1.4 dots per pixel for a sharp display. And the same goes for the 15″ iMac G3’s display, which looks great at 800 x 600, but fuzzy at 1024 x 768. [Editor’s note: This was written before Apple introduced the slot-load iMacs, which perform much better at 1024 x 768.]

Studies have shown that when scanning images for printed output, the image should be scanned at 1-1/3 to 1-1/2 times the final resolution – otherwise it will look fuzzy. The same principle is at work here.

As a general rule of thumb, a good monitor will have a horizontal dot pitch of somewhere around 0.22 (or a diagonal dot pitch of 0.25-0.28). Using the square root of 2 (1.414) as our factor, to achieve a specific sharp resolution, you must have a monitor of a minimum size.

resolution screen size
640 x 480 7.9″x5.9″ (9.9″ diagonal)
800 x 600 9.8″x7.4″ (12.3″ diagonal)
832 x 624 10.3″x7.7″ (12.9″ diagonal)
1024 x 768 12.6″x9.5″ (15.8″ diagonal)
1152 x 870 14.2″x10.7 (17.8″ diagonal)
1280 x 960 15.7″x11.8″ (19.6″ diagonal)

Keep in mind that this is viewable area, not the full size of the picture tube, and that this assumes about 0.22 horizontal dot pitch. This helps explain why a modified Color Classic can just support 640 x 480 with some hardware hacking (it has a viewable area just over 9″), but the iMac’s 13.8″ viewable screen isn’t sharp at 1024 x 768 – it’s two inches too small for that resolution based on its dot pitch.

My old Nokia monitor worked fine at 1024 x 768, but it simply didn’t look good at any higher setting. My Optiquest 19″ is great at 1152 x 870, but it doesn’t quite cut it as 1280 x 960. Yet the Sony monitor I use at work, a 21″ screen, supports 1280 x 960 beautifully.

How I Work

I spend a lot of time switching between Claris Emailer, Claris Home Page, my browser (usually Internet Explorer 4.5, but sometimes Netscape 4.7 or iCab 1.7), and a shareware URL manager called WebChecker. I find it works best if I keep Emailer on the left of the screen at about 600 pixels wide and nearly full screen height, WebChecker on the right at close to full screen height (I visit a lot of sites daily), and move the browser and Home Page windows as necessary. Much of the time I’m moving between Home Page and my browser, so it’s nice if those windows can be next to each other with little or no overlap.

Because I try to design my site to work well even on older Macs (and PCs) with smaller screens, I keep my browser window at about 640 pixels and set my Home Page preview to 640 x 480. To work side-by-side, that calls for a 1280 x 960 monitor. That’s what I have at work, and I love it.

But at home, until a few weeks ago I was living with 832 x 624 (or 1024 x 768 when the Nokia worked), which meant a lot more overlap between the windows. Not only does this look cluttered, but it takes longer to switch between applications when more of the screen needs to be redrawn.

Much as I’d love a 21″ screen, they’re pretty expensive. But when dealmac pointed to the Optiquest 19″ at $340, I jumped. (I paid about $450 for my 17″ Nokia 1-1/2 years ago.)

I’ve discovered 19″ is a bit less than I’d like, but it is a huge improvement over 1024 x 768. There’s a little overlap, but a lot less than there was. And with a little creative resizing, I can have my browser window and Home Page windows next to each other.

In fact, the main obstacle to my using an iMac is the need for such high resolutions for the kind of work I’m doing. I could work smaller, but below 1152 x 870, I lose efficiency.

Your work habits will determine how much screen you need. And once you know that, you can use the table above to decide the minimum viewable area you need to get it.

What About LCDs?

About now, some of you may be wondering, “What about laptops? Do they suffer from the same problems as conventional monitors?”

Happily, the answer is no. A dot on a flat panel display is a dot. Period. In fact, flat panel displays will look fuzzy at any setting other then their maximum. A PowerBook G3 with a 14.1″ 1024 x 768 screen is a thing of beauty, but 800 x 600 and 640 x 480 look fairly bad. Likewise, the clamshell iBook looks great at 800 x 600, but it simply isn’t crisp when displaying 640 x 480.

The only ways to have sharp resolutions other than at maximum resolution are for the maximum to be an exact integer multiple of the lower resolution (e.g., a 1280 x 960 screen displaying 640 x 480) or to only use a portion of the display to show the lower resolution.

This gives flat panel displays several advantages over traditional monitors, along with two disadvantages.

Advantages

  • tack sharp at their designed resolution
  • smaller display remains sharp (14.1″ diagonal provides a sharp 1024 x 768, where a CRT must have a viewable diagonal of at least 15.8″)
  • smaller footprint
  • very low power consumption

Disadvantages

  • fuzzy at any resolution other than the maximum (with rare exception of exact integer multiples)
  • expensive

For now, traditional monitors are the way to go unless you need portability or have a generous budget. But over time flat panel displays will continue to drop in price and increase in resolution. In fact, IBM recently shows screens that displayed 123 points per inch – that beats the 0.22 horizontal pitch of today’s good CRT monitors, and it’s tack sharp at that setting.

The day Apple announces a PowerBook with a 1280 x 960 screen is the day I prepare to retire my huge desktop with it’s big 19″ monitor. With IBM’s new technology, that PowerBook could have a 13″ display with 1280 x 960 resolution.

Update: When Apple announced the 15″ PowerBook G4 with its 1152 x 768 pixel display in January 2001, I put in my order. It was a bit less than I really wanted, but it served me well for years.

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