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WalVisions Home Theater Tutorial

Home Theater Home  -  Display Technologies  -  Best Image Size  -  Buying and Installation

Common Problems  -  Wall Visions  -  Calibration and Upkeep  -  Light Levels and Contrast


What is the Best Image Size?
Just how big an image is necessary for true home theater?

Let's start with the disclaimer - there is no "right" image size.  There are just too many variables to pick a universally correct size.  These variables include display quality and type, source quality, the viewing environment, and the biggest variable of all, personal preference.  But there are a number of factors and guidelines for you to consider, and with a little thought the right size for you should become apparent.  In this section we hope to provide guidance that will lead you to your optimally sized display.

Horizontal Viewing Angle

If you want to get that “being there” feeling, sufficient image size is essential.  A general rule of thumb for that "realistic" feeling is that the horizontal viewing angle should be at least 30 degrees, which means the viewing distance should be no more than 1.87 times the image width (1.63 times the diagonal for a 16:9 display).  Following this guideline, the maximum viewing distance for a 42” diagonal display is about 5.5 feet.  Looking at it from a different viewpoint, for a 10 foot viewing distance, the width should be a little over 64”, which corresponds to a diagonal of 73” for a 16:9 display.  Of course there are other factors, and there are no hard numbers - it would be ludicrous to suggest that viewing from 10 feet is OK but viewing from 11 feet is too far.  Let’s look in some detail at some of the other factors in determining the ideal image size.


Imagine the image size starting very small and then growing ever larger while you're viewing at a fixed distance. At first only the coarser image details are seen, and then smaller and smaller image details become apparent, and finally as the size is enlarged to the largest sizes the image will start to look “soft”, or blurry.  The goal is to find a viewing size that is sufficiently large, but also where the image appears sharp and where all image details can be seen (moving closer reveals no further detail).  Normal “20/20” eyesight can just resolve image details that are about 1/60 of a degree across (1 arc minute), and when the smallest details are about 1.5 times that size the image will still appear relatively sharp.  Using this as a guideline, for a 1080p (1920 pixels wide) display to appear sharp the viewer can be as close as about 1.1 image widths away, while for a 720p (1280 pixels wide) image he can be as close as about 1.75 times the image width away, and for a 480p (EDTV, 720 pixels wide) display he can be as close as about 3 times the image width away.

The below table shows the relationship between viewing distances ratios, viewing angles and resolution for the most commonly available 16:9 display resolutions.  For a given viewing distance ratio, the table shows the resulting horizontal viewing angle and how large the smallest image details will appear for the three common display resolutions.  We have graded these characteristics with good, very good and excellent labels.  For instance, the table shows that when viewing a 1080p display from 1.5 times the image diagonal, the image will be truly excellent, covering a 32 degree horizontal viewing angle and appearing sharp to someone with 20/20 vision (assuming the source resolution takes full advantage of the 1920 x 1080 format).  The table also shows that if a display will be viewed from 4.1 (or more) times the image
diagonal, even a 480p display will appear fully sharp - so a 1080p or 720p display is not needed for such an application.

Viewing Angles and Resolutions for Various Viewing Distances
to Diagonal
Viewing Distance
to Width
Viewing Angle
Smallest Detail Size - arc minutes per pixel
1080p Display
(1920 x 1080)
720p Display (1280 x 720) 480p Display
(720 x 480)
.87 1.00 53.1 1.66 2.49 4.43
1.05 1.21 45 1.41 2.11 3.75
1.20 1.37 40 1.25 1.88 3.33
1.38 1.59 35 1.09 1.64 2.92
1.52 1.74 32 1.00 1.50 2.67
1.97 2.26 25 .78 1.17 2.08
2.31 2.66 21.3 .67 1.00 1.78
2.70 3.10 18.3 .57 .86 1.53
4.14 4.76 12 .38 .56 1.00
Grading Key
Very Good

The table makes it apparent that the key for a true theater environment is to use high definition sources and true high definition displays (720p or 1080p).  To achieve about a 30 degree viewing angle and have an image which appears sharp, only these two HDTV formats are sufficient.  It also becomes apparent that for larger viewing distances (3 times width and beyond) the added resolution of a true HDTV will not be fully appreciated since the 480p displays will generally appear sharp.

[For a simulation on your PC monitor of how different resolutions will appear at various viewing distances, try the Viewing Distance - Resolution Simulator Pattern (WV-47).  The resolution and width combination of this pattern corresponds to a small section (1/10 the full width) of what would appear on a large screen display.  Thus if you want to see how various resolutions appear at "n" times the full image width, view the pattern at a distance of 10 times "n" times the measured pattern width.   For example, if the pattern measures 8" wide on your monitor and you want to see what viewing at 1.5 times the full width looks like, view from 120" (10 x 1.5 x 8").  The resolutions depicted are 853 x 480 (roughly 480p standard definition), 1280 x 720 (720p high definition), 1920 x 1080 (1080i/1080p high definition) and 3820 x 1920 (roughly 4K ultra high definition).  Note that this pattern is a very rigorous test, and intended to show the worst case - the pixels are black or white, and are "stepped" at shallow angles to be very revealing.  For viewing of normal video sources (i.e. not viewing computer graphics), the "steps" will be clearly less noticeable as the source material will have been specially filtered to reduce the possibility of unintended noise and patterns in the smallest image details.]

For fixed pixel digital displays, there is one other resolution effect that should be noted - the "screen door effect".  If these displays are viewed from close distances, the rows and columns of pixels may become apparent.  When each pixel spans over 1 arc minute, people with sharp eyesight may just be able to make out the individual pixels making up the image, and the screen door effect may be slightly visible.  For most people and displays the screen door effect isn't a problem with the Excellent and Very Good ratings above.  Additionally, many displays have incorporated smoothing features to lessen the effect, and some people are more sensitive to the effect than others.  This is one performance area that should be personally evaluated before deciding on the display type.

The Luminance (“Brightness”) Factor

While image “brightness” generally is not a factor for self contained displays, it can be a significant factor for the front projection systems that are necessary to achieve the larger image sizes.  Front throw projectors are characterized by a “lumen” rating, which corresponds to the projector's maximum light output capability.  When the screen area is doubled (1.4 times wider), the light is spread over twice the screen area, so the peak luminance (brightness) level drops to one half.  The necessary luminance level depends upon a number of factors, including other sources of light in the viewing environment and screen type, so there is not a “minimum” necessary.  At this point just be aware that for front projection the image size and necessary projector light output levels are related.  These levels are discussed in more detail in the Light Levels, Contrast, Gamma section.

The Personal Preference Factor

While there are guidelines that correspond to what most people desire, the optimum viewing size can vary significantly from person to person.  How close do you like to sit in a movie theater?  When in your “ideal” seat, clench you fists at arm’s length and measure how wide the screen is, in “fist widths”.  Each fist width is about 10 degrees – if you’re like most people the ideal screen might be 3 to 4 fists wide.  Or look at your computer monitor and imagine its displaying a movie or a sporting event – what is the ideal viewing distance to width ratio to make you feel like you’re a part of the action?  Here's an image (a little less than 720p resolution) you can view on your monitor - how many picture "widths" away gives you the best view.  You can use these and other similar techniques to determine just how big a display is ideal for your viewing distance.

In summary, for a truly involving home theater the display should have HDTV resolution, and the width should be such that the seating distance is no more than about 1.75 times the image width (1.5 times the diagonal for a 16:9 display).  For a 1080p display, seating can be as close as 1 times the image width for a truly immersive experience, but should be at least about 1.5 times the image width (1.3 times diagonal) for a 720p display.  For typical family/group viewing from distances ranging from 10 to 15 feet, this means that image sizes should be 6 feet wide (84” diagonal) and larger!  This is a key reason to give consideration to front projection systems which can provide ample sizes without excessive bulk and cost.  It’s also a reason to consider
Wall Visions!


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