Les écrans de portables : Taille, Résolution, et Lisibilité

Estimate Screen Resolution Appearance On Your Screen
Sometimes you want to purchase a laptop but you're not sure if its native resolution is too small for you. Furthermore, that particular model is not available for display around your area. One way to check if the resolution is OK for you is to look for photos of the laptop's screen while it's browsing a website. Sometimes you can't find a good picture on the web. But here's another way to estimate the look of a particular screen resolution on your very own screen:
 
Steps:
 
   1. Find your screen's DPI
      e.g. My resolution is 1440x900 on a 15.4" screen. DPI = sqrt(1440^2 + 900^2)/15.4 = ~110 DPI
      So for a q x w screen resolution on a screen with a diagonal length of s in inches, its DPI = sqrt(q^2 + w^2)/s.
 
   2. Find the DPI of the screen you want to try out (use same formula as above)
      e.g. In my case, I wanted to find the DPI of the VAIO Z which is 1600x900 on a 13.1" screen. Turns out to be ~140 DPI
 
   3. Find the scaling factor: (Your screen's DPI calculated in step 1) / (DPI of the screen you're interested in, calculated in step 2)
      e.g. Scaling Factor for me = 110/140 = ~0.7857 or 78.6%
 
      What does this mean? The screen of my laptop would look 78.6% as small on the VAIO Z. This doesn't mean I lose screen real-estate. It means that the text and images of my screen will just look 78.6% their original size (thus giving me more screen room in the higher DPI screen). If you get a number higher than 1.0 (100%) then it means the screen you want to try out has a lower DPI and thus text/images would look larger on that screen.
 
   4. Take a screenshot of your laptop using the Prt Sc key, preferably a screenshot of a website you read all the time or one with the smallest sized text you normally read.
 
   5. Paste the screenshot into Photoshop or your favorite image editor, one that can re-scale images bicubically (it's an Image Size... option in Photoshop, should be similar in GIMP). Make sure you are viewing the image at 100% zoom. Then re-scale the image by percentage using the scaling factor you calculated in step 3.
 
      In my case, I pasted the screenshot into Photoshop and pressed Ctrl+Alt+0 to zoom to 100%. Then I went to Image->Image Size... and I set it to scale by percent and I entered 78.6 for both width and height. I also set the Resampling method to Bicubic (bilinear should work here as well I think).
 
      See "Other Ways to Use the Scaling Factor"
 
   6. And now you should have an "estimation" of how things would look at the resolution you're interested in. I say estimation because the re-scaling does blur the image a little bit so you can think of this as a worst-case estimation. The actual look should be much sharper on the real screen. This is to help you get an idea of the size appearance of text/images.
 
 
Other Ways to Use the Scaling Factor
Head Distance Method (suggested by ac500):
Pick a viewing distance from the monitor to your head. Take that distance and divide by the scaling factor from step 3. The resulting distance should be where you need to view your screen from to simulate how the desired screen resolution would look. It's pretty accurate!
 
Example: Currently I'm viewing my screen from 2ft away. The distance I need to move my head is 2ft/0.7857= ~2.5ft. So viewing my screen from 2.5ft should be similar to viewing the VAIO Z from 2ft away.
 
Word Processor Method (suggested by hendra):
Use the scaling factor to adjust the zoom level of your word processor. For example: with a 0.7857 scaling factor, I need to adjust the zoom level to 78.57%. Word 2007 has this option and other word processors should too. You can paste text and adjust font sizes to see how font size 8 text, for instance, would look at your target resolution. It's a good method to clearly see how text would look as blurring doesn't occur when re-scaling in a word processor.
 
So I hope this was useful for those who don't have the means to see the laptop in person like me first instance. I haven't seen anyone post this before so I thought maybe this can help people out especially since it's a common question for potential Z buyers. If there are any flaws or mistakes, let me know!

Good idea, although the blur effect you mentioned can definitely mess up the results a little. For example, scaling my text to look the size of the high res Sony Z looks very hard to read, but in real life it looks just as sharp and easy to read as my 17" 1280x1024 monitor.
 
Another measurement is to choose a certain monitor-head distance (like 2 feet, for example), then divide your that distance by the DPI scaling ratio you described, and place your head at the resulting distance from your current monitor. You will then get an accurate representation of how easy text would be to read at your chosen distance of 2 feet or whatever.