I have seen a few questions over the years by players just upgrading to a new monitor with higher resolution and wondering why they still see jaggies and need anti-aliasing. It is always a similar story:
I just bought a new 21.5″ monitor and 1920×1080 resolution. My old monitor was only 1024×768. I thought people said you don’t see jaggies with this high resolution. Is something wrong with my monitor?
The pixels on a typical monitor are pretty small. You would think we would not be able to see them while sitting two or three feet away from the monitor. Well the individual pixels are hard to see, but jagged edges are not. They are most common when a line drawn on the screen is near vertical or horizontal but not quite. Our eyes are able to pick up the stair-steps in the line pretty easily.
Anti-aliasing (multisampling in computer graphics) is a way to smooth this out by rendering jagged parts of the image at higher resolutions (2x, 4x, etc.). Then scaling those higher resolution parts back down to the original resolution. This blurs the edges of all the lines just a tad and covers up a lot of jaggedness in the final image. At first glance it would seem we just need higher resolution monitors, but it is a little more complicated than that.
You see, monitors will always have a finite number of pixels, so there will always be jagged edges. However, the human eye can only see so many pixels. If the pixels are small enough, our eye cannot detect them. That means no more jaggies. Well, they are still there. We just do not see them anymore.
So it is not really the resolution but the size of the pixels that makes the difference. They have a term for this, pixel density, and it is measured in pixels per inch (ppi). According to Bryan Jones, Ph.D, retinal neuroscientist at the University of Utah, the eye is only capable of seeing 287 ppi. Note that this is based on the average human eye. Some people might have more sensitive eyes and see maybe 300 ppi while others can only see 250 ppi.
All you need is a computer monitor that can display 300 ppi. To see how far we have to go, let us just calculate the pixels per inch on that 21.5″ monitor with 1920×1080 resolution. Since monitor sizes are given in diagonal inches, the easiest way to calculate pixel density is dividing the diagonal pixels by the diagonal inches. So monitor resolution does play a factor, but that is only half of the equation.
Now, most monitor manufacturers do not list the diagonal inches of the viewable area, so I will just assume that 21.5″ is the viewable area. For your own monitor you can easily use a long ruler (24″-36″ is good) or tape measure. The slightly harder component to calculate is diagonal pixels. This can be done using the Pythagorean Theorem everyone learns in middle school:
sqrt(1920^2 + 1080^2) = ~2203 diagonal pixels
Now, we simply divide the diagonal pixels by the diagonal inches:
2203 pixels / 21.5″ = ~102.5 pixels per inch
That is pretty far from 300 ppi. The desired pixels density is roughly three times as much as what we have with this monitor. Using these same concepts we can come up with a theoretical monitor that would achieve 300 ppi. If we could reduce the monitor size three times, a 7.17″ monitor with 1920×1080 resolution would have 300 ppi. A small monitor is not ideal for gaming though. To get 300 ppi on a reasonable sized monitor of 21.5″, we would have to increase the resolution to 5760×3240, an incredible 9 times the pixels of the standard 1920p resolution available today.
Apple is getting pretty close to 300 ppi with their new Retina Display on the iPad 3. It features a 9.7″ screen with a resolution of 2048×1536. The resolution is actually higher than 1920×1080, but the diagonal inches are too high at 9.7″. The product page for the iPad 3 even states the screen has 264 pixels per inch. That is not high enough for looking at the screen two to three feet away but definitely enough for one foot or less.
We are not at the point of eliminating jagged edges. The iPad 3 is pretty close, but it is too small to be a computer monitor. We need a large size monitor that can output extremely high resolutions. However, there is another problem as far as games are concerned. Nine times the pixels means roughly nine times the work the video card has to do (and partly the processor too). Video cards are just barely becoming capable of life-like visuals. They are just not powerful enough to display nine times the pixels and still maintain the same overall visual quality.
I always like making predictions, so my guess is that it will not be for another 10 years that we see a computer monitor capable of 300 ppi available to consumers. The tablets will probably get there first with Apple’s pushing, but computer monitors do not have a big company pushing them to do more. Most monitors are used for office work, where high resolution is not really needed. Because of this relative lack of demand for higher ppi monitors, there is not much incentive for companies to push the envelope.
Until then we will just have to continue using anti-aliasing in our games and ignore any jaggies we still see.