The Gamer's Graphics & Display Settings Guide

[Page 6] Graphics Settings - Resolution



Resolution


Display resolution, often simply called Resolution, refers to the total amount of visual information on a display screen. In computer graphics, the smallest unit of graphical information is called a Pixel - a small dot with a particular color and brightness. Every computer image on your screen is a pixellated sample of the original 3D information contained in your graphics card, because that is how it winds up being displayed on a monitor. When you change the resolution in a game, you are telling the game to provide more or less pixels, and hence more or less samples of that original information for your system to process and display on screen. In general the higher the resolution, the clearer and better the image will look, but the more effort this will take for your system to draw all this information, resulting in lower FPS.


The resolution setting in a game or in Windows tells you precisely how many pixels are used to display an image. Resolution is typically shown in pixel width x pixel height format. So a game running at '1280x1024' resolution for example means there are 1,280 x 1,024 = 1,310,720 pixels in total on the screen making up the image. This value can also be expressed in Megapixels (millions of pixels), which in this example would be around 1.3 megapixels. The human eye takes all these pixels and at a reasonable distance perceives them as a single smooth image, much like looking at an image in a newspaper from a distance as opposed to close up.


To understand the practical aspects of resolution better we need to look at the structure of the types of screens on which pixels are displayed.


Dot Pitch


The screen on a CRT monitor is made up of lots of tiny Phosphors. It is these phosphors which glow briefly when struck by the beam from the electron gun inside the monitor and produce the image we see on a CRT screen. In Aperture Grill type CRT monitors, the phosphors are separated into fine red, green and blue vertical strips; in Shadow Mask type CRT monitors, the phosphors are separated into groups of tiny red, green and blue dots.


A pixel may be the smallest unit in computer graphics, but a single pixel on a CRT monitor is still made up of several phosphors. At maximum resolution on a CRT monitor, a single graphics pixel is made up of a 'triad' of phosphors: one red, one green and one blue phosphor. These three are necessary to generate all the required colors of a single pixel.


We refer to the distance between similar-colored phosphors as Dot Pitch, which is measured in millimeters. Effectively, this is a measure of how big the smallest possible pixel would be on a CRT. The lower the dot pitch, the finer the image the CRT display can show, and typically the higher its maximum supported resolution. Most modern CRT monitors have around 0.28 to 0.25mm dot pitch, though some manufacturers also tend to be deceptive and quote this incorrectly so your actual dot pitch may be slightly higher than quoted.


Importantly, a CRT displays graphics using a moving electron beam which is manipulated magnetically and projected onto the phosphors on the screen. This along with its large number of phosphors basically means that a CRT monitor can rescale an image to a series of resolutions up to its maximum resolution without any noticeable degradation in image quality. The reason for this is provided further below. Note that there may however be slight differences in image quality at different resolutions on a CRT due both to the dot pitch and also the refresh rate.


Fixed Pixel Structure


LCD monitors differ from CRT monitors in that they do not have an electron beam or lots of tiny phosphors lighting up. Instead they display images using a grid of fixed square or rectangular Liquid Crystal Cells which twist to allow varying degrees of light to pass through them. Just like a phosphor triad however, each LCD cell has a red, green and blue component, again to facilitate proper color reproduction for each pixel. Even though many LCD monitors are now approaching the point at which the distance between these cells - their 'Pixel Pitch' - is similar to the Dot Pitch of a CRT, because of the way LCDs work and their fixed cell composition, LCD monitors can only provide optimal image quality at their maximum supported resolution, otherwise known as the Native Resolution. At other resolutions, the image can appear more blurry and exhibit glitches. The reason for this is covered below.


Analog vs. Digital


The fundamental difference between a CRT and an LCD monitor is that a CRT monitor is based on Analog display technology, while an LCD monitor is a Digital display device. Analog signals are continuous and infinitely variable, whereas digital signals come in discrete steps.


A CRT monitor only accepts analog input. Thus a graphics card's RAMDAC has to convert all the digital image information into analog before sending it to a CRT monitor. The monitor then continues to use analog information internally in the form of voltage variations, electron beams and magnetic fields to paint the picture on your monitor screen, resizing it as necessary to fit the display space. The results are similar to an image from a movie projector being thrown onto a wall and being adjusted to fit as required, such as moving the projector closer or further away, and adjusting the focus.


An LCD monitor on the other hand can receive either digital or analog information depending on its connection type, but it always needs to convert any analog data to digital form eventually before using it. At resolutions which are lower than its native resolution, the monitor has to digitally rescale an image to fit into its fixed pixel structure. At times when the image doesn't fit evenly into the lower resolution, bits and pieces of it will show visual glitches and blurring, because the monitor has to Interpolate (guess) some of the data to make it all fit. It's like creating a range of different sized images out of a fixed number of small Lego blocks; some will fit perfectly, others will have oddities because you can't split a Lego block into thirds for example.


The bottom line is that digital information is discrete and precise, while analog information is continuous and imperfect. That is why an LCD monitor running at its native resolution shows a much sharper image than a CRT monitor at the same resolution. But once resolutions are changed the LCD monitor has a much harder time rearranging everything to fit properly, while a CRT monitor has no trouble at all.


Aspect Ratio


The ratio of the pixel width of any given resolution to its pixel height is called the Aspect Ratio. Using an example of a 1280x1024 resolution, the aspect ratio is 1,280/1,024 = 1.25, which expressed as a ratio is 5:4. The standard aspect ratio for most computer monitors is 4:3, and the standard aspect ratio for the 'widescreen' format (used mainly by High Definition Televisions) is 16:9. Resolutions which precisely match the aspect ratio of your monitor will display correctly, while those that do not have the same aspect ratio will result in distortions to the image, such as a 'squished' image, or black bars to the sides or top and bottom of the screen.


Almost every CRT monitor is a standard 4:3 aspect ratio, and this is always accommodated by games since it's the most common ratio. On LCD panels however things can become a bit more difficult as some are widescreen 16:9, some standard 4:3, and some slightly different to both these. For example an LCD with a native resolution of 1280x1024 is 5:4 aspect, which means that at resolutions outside its native resolution, the image will be ever-so-slightly more or less wide than it should be. See Resolution Tips below for some ways of attempting to resolve scaling issues if it bothers you.


Interlace & Progressive


Something I haven't described in great detail yet is the way in which a CRT monitor actually draws the screen image. I cover this in more detail under the Refresh Rate and Response Time sections, but something I don't cover elsewhere are the concepts of Interlace and Progressive. This is not an issue of any major concern on PC monitors, as all of them use progressive which is optimal. However since more people are hooking up their PCs to HDTVs (High Definition TV), this is very relevant to that technology.


Without getting into a huge amount of detail, interlacing is a compromise trick developed for traditional CRT TVs early on to allow them to use the existing amount of information to display higher resolution images and also double their refresh rate from 30 to 60Hz to prevent noticeable flickering. It does this by alternately displaying all the odd-numbered horizontal lines in an image, then displaying the even ones, and back again. Our eyes, due to persistence of vision, do not notice the gaps - we see an entire image made up of odd and even lines.


However interlace is not as optimal as progressive scanning, which basically draws the entire image on screen as a single completed frame without breaking it up into these odd and even fields. A whole frame displayed at 60Hz provides better image quality and less flicker than interlaced fields displaying at 60Hz.


So when gaming on an HDTV you may see resolutions denoted as 576i or 480i, or 720p for example. The numerical part indicates the pixel height of the screen, and the i or p after the numbers denotes interlace or progressive. In general the same resolution looks better using progressive (if supported on your display), and on fixed-pixel displays like LCD or Plasma HDTV, the closer the pixel height is to your display's native resolution, the better it will look.


Resolution Tips


Let's take some time to consider how we can use the information above to enhance gaming. For starters, higher resolutions typically bring with them a reduction in the jaggedness of outlines in computer graphics. This is precisely what Antialiasing tries to do as well. So it is often wise - especially on systems with fast graphics cards combined with slower CPUs - to consider raising your resolution and turning off or reducing any antialiasing to get a performance boost with no real drop in image quality.


For LCD monitor owners, there is a simple trick you can use to boost performance and also get some 'free' antialiasing: that is to run a game just below your native resolution. For example, running a game at 1024x768 on a 1280x1024 LCD may sound odd at first, but aside from the FPS boost you get from lowering your resolution, the slight blurring from running at a non-native resolution reduces the harshness of jagged lines, courtesy of your monitor's attempts at rescaling the image with interpolation. This is not as good as real antialiasing, but it's worth a try if you need the extra FPS.


Finally, to get the optimal image quality on an LCD display at non-native resolutions, you need to adjust your scaling options in the graphics card control panel. The details are provided under 'Digital Flat Panel Scaling' on this page of my Nvidia Forceware Tweak Guide, and on this page of my ATI Catalyst Tweak Guide under 'Digital Panel Properties'. You can both increase image quality by forcing your graphics card to rescale an image before sending it to your monitor, and also fix any aspect ratio-related problems using these settings, however note they only work for LCD monitors connected via DVI, not via VGA. The reason for this is that the digital scaling unit on your monitor is usually inferior to the scaling capabilities of your graphics card which is working with the source data.