Saturday, June 02, 2007

23. LCD Resolutions and Ratios (Part 2)

by orev
From Notebook Review

When you're looking for a laptop (or any type of screen), one of the things you should look at is the screen resolution. Some people care more about the size of the screen, but to me, it's both the size and the resolution that are important. The more pixels on the screen, the more stuff you can see at once.

While shopping recently for a laptop, I kept coming back to the question of: "Will the display resolution at this screen size be too big or small for me to read comfortably?" My current monitor has a nice size, and I wanted to be able to compare my monitor with the laptops out there. Of course, I can't take my monitor everywhere to compare.

This led me to the idea of looking at the DPI, or "Dots Per Inch". DPI measures how many dots (pixels) there are in 1 inch across or down on the screen. Because this measurement is specifically tied to a physical measurement, you can be sure that no matter what the resolution of the screen is, the DPI will tell you exactly how it will look.

I calculated the DPI for many common screen sizes at common resolutions, allowing a very direct comparison of DPI for these different screens. Here are the charts, broken down by aspect ratio (and you thought that learning the pythagorean theorum and all about sin/cos/tangents was useless!):

Widescreen Format (16:10) Display DPI Resolution
12.1 250x249 187x187 164x164 140x140 125x125
14.1 214x214 161x160 141x140 120x120 107x107
15 201x201 151x151 132x132 113x113 101x101
15.4 196x196 147x147 129x128 110x110 98x98
17 178x177 133x133 117x116 100x100 89x89
19 159x159 119x119 104x104 89x89 79x79
20 151x151 113x113 99x99 85x85 76x75
22 137x137 103x103 90x90 77x77 69x69
24 126x126 94x94 83x82 71x71 63x63
27 112x112 84x84 73x73 63x63 56x56
30 101x101 76x75 66x66 57x57 50x50

Standard Format (4:3) Display DPI Resolution
1280x960 1024x768
12.1 165x165 145x145 132x132 106x106
14.1 142x142 124x124 113x114 91x91
15 133x133 117x117 107x107 85x85
17 118x118 103x103 94x94 75x75
19 105x105 92x92 84x84 67x67
20 100x100 87x88 80x80 64x64

SXGA (5:4) Display DPI Resolution
12.1 135x135
14.1 116x116
15 109x109
17 96x96
19 86x86
20 82x82

Some of those size/resolution combinations don't exist (you'll probably never be able to get a 12.1" screen with a resolution of 2560x1600).

OK, how do you use these charts?
  1. Figure out the resolution and size of your current display. To find the size of your display, take out a ruler and measure diagonally from corner to corner. To find the resolution, right-click on your desktop, choose Properties, then go to the settings tab. You will see a slider with the "screen resolution" listed.
  2. Look up your monitor on the chart. For example: if you have a standard (4:3) format 17" display, with a resolution of 1400x1050, then your DPI is 103x103.
  3. Now you can look at other DPI numbers in the chart and see what else matches up to your monitor.
One thing that many people worry about is if "things will be too small" on the monitor. It's true that the higher the resolution and DPI (bigger numbers), the smaller pictures and fonts will be on the screen. However, you can adjust the font settings to compensate for this on the Display control panel, using "Large fonts", or you can specify what DPI you have. This can make some of the Windows UI look out of proportion, though I hear that in Vista this should not happen. The advantage of doing this is that you will see much better resolution with photos, and fonts will also display more clearly (kind of like using cleartype). Many programs (like MS Office, Firefox) also have a "zoom" feature, that lets you make the fonts look bigger on the screen without changing how big they will be when printed.

Some notes on DPI:
  • Bigger numbers mean smaller letters on the screen.
  • Windows generally assumes you have a 96dpi display, no matter what you ACTUALLY have. At the moment, it's not possible (AFAIK) for Windows to automatically know what the actual DPI is without you telling it.
  • I'm not sure how much this relates to DPI settings in Photoshop or other programs like that
  • You can compare this to printed paper too. As far as I know, printed material is usually around 300 dpi.

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