Which is better, XGA or SXGA+?

[cplusplus]

I feel too many peoples have asked the exact same question, and too many answers are provided. To save us all time, I hope this is going to be the very last thread on this subject and provides a complete and accurate assessment of XGA versus SXGA+ given a typical 12" tablet PC.

Please correct me if I'm wrong, and add additional information that you see fits here. Thanks.

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Concepts:

Physical size : the size of a physical object, measured in inch.
Physical DPI: dots per inch in physical size (used to measure the size of each physical dot).

The size and the resolution of the physical monitor decide its physical DPI.

With 12.1" XGA monitor,
12.1" inch mapped to (1024^2 + 768^2)^0.5 = 1280 dots
This translates to 1280/12.1 = 105 DPI

With 12.1" SXGA monitor,
12.1" inch => (1400^2 + 1050^2)^0.5 = 1750 dots
This translates to 1750/12.1 = 144 DPI

Due to different physical DPIs, 12.1" SXGA+ can display up to (1750/1280)^2 = 1.8692 = 187% as many dots as 12.1" XGA can display. In other words, 12.1" SXGA+ delivers 87% more screen real estate.


Logical size: the size that the monitor thinks a displayed object has.
Logical DPI: dots per inch in logical size.

The operating system controls the logical DPI and applies it to the software that has to rely on the operating system for displaying something on the screen. In Windows systems, it is set to 96 DPI by default, which means Windows thinks 1 inch is displayed with 96 dots on the screen.

On a 12.1" XGA tablet PC, if you draw a 1-inch line on screen, it covers 105 physical dots. If Windows uses the default 96 logical DPI, the 1-inch line is considered by Windows as 105/96 = 1.0938 inch in logical terms. In other words, when you draw a 1-inch line, Windows thinks you have drawn a 1.0938 inch line. And when Windows thinks you have drawn a 1-inch line, you have only drawn 96/105 = 0.9143 inch in physical terms.

On a 12.1" XSGA tablet PC, by the same mapping rule, when you draw a 1-inch line, Windows thinks you have drawn a line of length = 144 / 96 = 1.5 inch. And when Windows thinks you have drawn a 1-inch line, you have only drawn 96/144 = 0.6667 inch physically.

Due to different physical DPIs, 12.1" SXGA+ displays 1 inch x 1 inch = 1 square inch area using 0.6667 x 0.6667 = 0.4445 square inch in physical terms. The 2-dimension size of any text is reduced by about 56% when Windows tries to display the text.

In contrast, 12.1" XGA displays 1 x 1 = 1 square inch area using (96/105)^2 = 0.8359 square inch in physical terms. The 2-dimensional size of any text is only reduced by (1-0.8359) = 0.1641 = about 16% when Windows tries to display the text.

We may change Windows's logical DPI from 96 to 120 to effectively increase the size of the text displayed on the screen. With 12.1" SXGA+ and 120 DPI, 1 square inch area is displayed as (120/144)^2 = 0.6944 square inch logically. Compared to the text size at 96 DPI, the size of text at 120 DPI is only reduced by about 30% when Windows tries to display it. The increased logical DPI makes text size larger and thus easier for human eyes to read.


Zoom factor: when a stylus writes on the LCD monitor, the capturing software may apply a zoom factor to the logical DPI, which determines the zooming effect. If zoom factor is 100%, there is no zooming effect, and 1 inch physical length is 105/96 = 1.0938 inch in logical terms for XGA, or 1.5 inch logically in the case of SXGA+. If zoom factor is set to 50%, the logical length of 1 inch is doubled to 2 inch in logical terms. If zoom factor is set to 200%, the logical length per inch is halved to 0.5 inch in logical terms.

Because the zoom factor changes the mapping ratio between physical and logical length, with a zoom factor larger than 100%, if you write on the LCD screen as you regularly would, the normal-sized characters will be translated into the characters that are smaller when displayed with no zooming effect.

By using a certain zoom factor larger than 100%, you can write larger characters on 12" SXGA+ screen for them to be captured as regular sized characters. By using a certain zoom factor smaller than 100%, you can write smaller characters on 12" XGA screen to be captured as regular sized characters.


Let's get down to a little math.

Formula:

logical length = physical length * physical DPI / logical DPI * zoom factor


SXGA+

If you have a 12" SXGA+ screen with 96 DPI:

Logical length of 1 inch on XSGA+
= 1 * 144 / 96 * 100% = 1.5 inch

Because 1 inch in handwriting is captured as 1.5 inch by default, you have to write much smaller characters than you normally would, in order for them to be captured at the size you think your handwriting has. What you see you have written on the screen is quite different from what the tablet PC (i.e., the capturing software) thinks has been captured.

However, your handwriting experience with SXGA+ tablet PC can be changed. If you change default DPI to 120 and set the capturing software's zoom factor to 120%:

Logical length of 1 inch on SXGA+
= 1 * 144 / 120 * 120% = 1 inch

As you can see, now 1 inch is captured exactly as 1 inch, which has the effect of what you see is what you get. This should make your handwriting feel natural - close to the experience when you write on paper.


XGA

If you have a 12" XGA screen with 96 DPI:

Logical length of 1 inch on XGA with 96 DPI
= 1 * 105 / 96 * 100% = 1.0938 inch

Since the physical to logical ratio is close to 1, you have a very natural handwriting experience by default: in terms of size, what you think you have written on the screen is almost the same as what the tablet PC (i.e., the capturing software) thinks has been captured.



SXGA+ versus XGA

1) By default, given that the physical size of the tablet PC monitors are the same, SXGA+ delivers 87% more screen real estate than XGA does, whereas XGA delivers natural sized characters and comes with 87% larger text than if displayed on SXGA+.

2) XGA delivers natural handwriting experience by default, whereas SXGA+ tablet PC can be adjusted to achieve the equally natural handwriting experience that XGA delivers by default.

Among such possible adjustments for SXGA+, the most important is the changing of logical DPI. The problem is: in general, if logical DPI is changed to any value other than the default 96 DPI, the graphical user interfaces of many software will appear to be distorted in the forms of clipping, overlapping, and so on. Windows Vista is able to linearly scale the graphical user interfaces based on the actual logical DPI. But unlike graphical images, text is not linearly scalable. As a result, when Vista tries to linearly scale up a graphical user interface, characters may become fuzzy. Generally speaking, Vista lessens the distortion caused by changed DPI but it does not solve the problem. (NB, everyone can experience the distortion by setting Windows DPI to 200, rather than 120 or 150.)

Note that when default DPI is changed to 120 or other value for SXGA+, SXGA+'s screen real estate is reduced accordingly, and the larger screen real estate is the single biggest sale point for SXGA+ versus XGA for typical 12" tablet PCs.

In conclusion, on a small tablet PC, XGA LCD monitors cost less and generally deliver what is expected of a regular laptop screen, as well as a natural writing experience. SXGA+ LCD monitors greatly improve on graphic display, but there is a considerable tradeoff for choosing the higher resolution of SXGA+, including (not limited to) small texts and less natural writing experience by default.


A real-world case:
ThinkPad x60T's SXGA+ versus LifeBook T4220's XGA

(This is based on personal experience with ThinkPad x60 Tablet's 12" SXGA+ and LifeBook T4220's 12" XGA; other tablet PCs' LCD monitors may exhibit different characteristics.)

ThinkPad's SXGA+ is generally bright enough for indoor use, but it seems substantially dimmer when used outdoors and when used in an office environment lit with bright fluorescent lights. Fujitsu's XGA is perceivably much brighter than ThinkPad's SXGA+ and is equally bright in different lighting conditions when used indoors.

If you do graphical design or digital darkroom processing, you may be sensitive to the color space of your laptop's LCD. LifeBook's XGA seems to deliver the natural colors as expected of a decent LCD nowadays. ThinkPad's SXGA+ is not only less bright, but also seems to be less color correct than LifeBook's XGA. All my photos had a stronger color casting when displayed on ThinkPad's SXGA+ screen.

In conclusion, on the one hand, no doubt, ThinkPad's SXGA+ has 1 distinct, desirable-to-many advantage over LifeBook's XGA: namely, its higher resolution screen of 144 physical DPI. This results in smoother shapes, clearer texts (especially when displayed using tiny fonts), and substantially larger screen real estate (in logical terms). On the other hand, the tradeoff for the higher resolution of SXGA+ as well as certain other LCD characteristics (such as brightness) become the advantage of LifeBook's XGA. Also, Fujitsu's professional notebooks are known for good quality*.

* Fujitsu has a public white paper on notebook quality, published early in 2007, available at its website, which details what tests Fujitsu professional notebooks must pass in order to be put on the market.

[airgaps]

clap clap clap !! Wow...really impressive review..should be stickied for reference of all of us (I have asked the question before jeje! ) and for others to come!! Extremely enlighting. Thanks for sharing.

[manhattan]

Awesome!

Maybe, if you feel like it... one day you could throw in WXGA & WXGA+ into the mix. But it does look like a lot of work for each resolution type and WXGA+ is not too different from SXGA (1440x900) & WXGA is not too too far from XGA (1280x768 sometimes 1280x800).

With the information you've provided; I guess these other common -yet not too common types of tablet LCD resolutions can be calculated.

Thanks for putting this up. Quite insightful.


edit:
I can see where the DPI can be adjusted. But where does one adjust the Zoom Factor?

[P8RSON]

Worthy of being a 'Sticky'....... and done.

[Xiao-Yue]

Thanks for this. Makes things completely lucid.

[EijiJC]

Thanks for the nice explanation. It helps clear up a lot of questions. One thing that slightly confuses me though, for the size capturing on the SXGA, does that size difference only appear when you print out the document or is there a difference on mark you make with the pen and the mark that appears on the screen? (E.g. you make a 1" line but the screen displays an additional .5") I'm assuming its the first one but if anyone could help clear it up it would be greatly appreciated.

[daver]

excellent post, and very clear indeed...

but now i have another question for you...
what about VGA?!?

[kureshii]

For a short summary, read the first 3 paragraphs of the VGA wiki.

[daver]

For a short summary, read the first 3 paragraphs of the VGA wiki.

i was just kidding about the VGA thing :P i was merely trying to crack the worst joke possible in this thread

[P8RSON]

i was just kidding about the VGA thing :P i was merely trying to crack the worst joke possible in this thread

What a splendid idea....

The worst possible joke Topic.

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