Selecting Display Size Based on Room Size and Seating

Transcription

1 CEDIA WHITE PAPER Selecting Display Size Based on Room Size and Seating 2014 CEDIA

2 TABLE OF CONTENTS 01 Introduction 3 02 Visual Acuity and TV 3 1. How Humans See 3 2. How Vision is Measured 3 03 How Images are Created on Displays 4 04 Vertical Viewing Angle 4 05 Horizontal Viewing Angle 5 06 TV Size and Seating Distance 5 07 Calculating Screen Size 6 08 Conclusion 7 09 References 7

3 01 INTRODUCTION The purpose of this whitepaper is to discuss recommended methodologies for determining the ideal display size for multi-purpose areas based on room size and seating location. The size of a display screen can determine the satisfaction level of a viewer s experience and is dependent upon the viewer s position and their distance from the display. The recommendations outlined in this document are for displays with 1080p resolution and an aspect ratio of 16:9. This paper will not touch on display selection for a dedicated home theater because that information was addressed in CEA/CEDIA- CEB23: Home Theater Recommended Practices: Video Design, which is available in the CEDIA Marketplace at The recommendations in this paper are determined by combining knowledge of human visual capabilities and the current display technology available to consumers. Recently, 4K displays have become available for theaters and consumers, but because 4K displays are still less common than 1080p, those recommendations will be discussed in a separate whitepaper which has not yet been published as of the writing of this document. 2. HOW VISION IS MEASURED Visual acuity is most commonly measured using the Snellen chart in an eye exam. A Snellen chart is made of several lines of letters of smaller and smaller sizes. An individual reads the letters in each line and the accuracy of their identification indicates their visual acuity. Individuals who can accurately discern the 20/20 line of letters fall within the average performance for humans and are said to have 20/20 vision. Most Snellen charts have lines that go beyond 20/20 vision (to 20/15 and even 20/10) to identify how precise a person s visual acuity is in each eye. For example, a person with 20/10 vision is able to see detail from 20 feet away that an average person can only discern from 10 feet away. Snellen charts can be designed to look at visual acuity from varying distances but are always based around the 20/20 line where letters are separated at 1 arc-minute. Arcminutes are angular units of measurement that are equal to 1/60th of a degree. 02 VISUALACUITY AND TV 1. HOW HUMANS SEE The recommendations included in this document are based on an aspect of human biology known as visual acuity, which is the measurement of how well individuals can discern visual information. Humans see objects when light that bounces off of or originates from an object is reflected by the eye lens onto the retina. The retina then sends the information to the brain to process the image. An average person has a vertical viewing angle of 100 and a horizontal viewing angle of 120. Because humans have relatively weak peripheral vision, the edges of the field of view are often blurry and unfocused, an effect that is important to understand when determining how a person will get the best image out of their display. Figure 1: Snellen Chart [1] 2014 CEDIA 3

4 03 HOW IMAGES ARE CREATED ON DISPLAYS Displays are able to produce visible images because of elements called pixels. Pixels (short for picture element ) are the smallest components of a digital image and are made up of red, green and blue subpixels. These colored pixels are arranged in a grid within the display which is then lit in different patterns to reproduce images and movement on the screen. The number of pixels present is used to classify the display device s resolution. Resolution is typically measured by multiplying the pixels along the device s width by the number of pixels along the device s height, and rounding to the nearest tenth. In the world of consumer video, manufacturers commonly identify resolution in terms of vertical measurements only, which is why consumers see displays classified as 780p and 1080p. The more pixels available per square inch, the greater the resolution and the more accurately an image can be reproduced. For this document, only 1080p resolution displays are being discussed because they are most commonly used for multi-purpose displays for the home. 04 VERTICAL VIEWING ANGLE When selecting display sizes, arc-minutes are used to measure the minimum number of pixels required to produce enough visual data to achieve the maximum experience of visual detail for a viewer. This is because one arc-minute is the smallest observable detail that a person with 20/20 vision can see. If the number of pixels in the display is equal to or greater than the number of arc-minutes within the current field of view, maximum viewable detail is achieved. Conversely, if the viewer can discern more detail than there are pixels, a suboptimal experience will result. Therefore, when the number of vertical lines of resolution in the display is equal to the number of arc-minutes within the vertical viewing angle, the optimal viewing experience is achieved. Assuming a display with a vertical resolution of 1080 pixels and a viewer with 20/20 vision, the optimal viewing angle can be calculated by dividing the vertical resolution by 60 (the number of arc-minutes per degree). The vertical viewing angle is important because it defines the relationship between the seating location and the size of the display. If the viewer sits too close to the 1080p display, he or she will have a viewing angle greater than 18 and will have the ability to discern the spaces between the pixels and therefore see jagged outlines or experience the screen door effect in the images viewed. Vertical viewing angle = Vertical viewing angle = p Display 18 Figure 2: Vertical Viewing Angle CEDIA

5 05 HORIZONTAL VIEWING ANGLE While humans discern detail in the vertical plane, they experience envelopment horizontally. Because of the frontal placement of the eyes, humans can see best within a 30 to 35 horizontal range when they look straight ahead. For the purposes of remaining near the ideal angle of vision (30 ) and providing a slight feeling of immersion, this whitepaper suggests using an average of 33 as the ideal horizontal viewing angle. 06 TV SIZE AND SEATING DISTANCE While some believe bigger is better when it comes to display size, home multi-media room displays are still vastly undersized compared to the ideal display size for the room. The layout of the room and the positioning of the seats also play a role in how satisfied a customer will be with the final result. Determining the correct display size and positioning can make or break a room, so it is important to know how to calculate the minimum size display that the consumer should use. While recommending a display larger than necessary may be acceptable depending on the specific application, if the room has a display smaller than the minimum recommendation, the viewer will not experience any feeling of immersion and may be dissatisfied with the final room configuration. In summary, when recommending a display size, in order to preserve the experience most displays strive to provide, the ideal vertical viewing angle for a 1080p display is 18 and the ideal horizontal viewing angle should be 33. W H Seating Distance 33 Figure 3: Horizontal Viewing Angle 2014 CEDIA 5

6 07 CALCULATING SCREEN SIZE The formulas for applying the above information rely on two variables: viewing distance and screen size. Because many clients have a predetermined seating location, it is common practice to specify a screen size based on the viewing distance. Assuming a vertical resolution of 1080 pixels and a viewer with 20/20 vision, ideal screen size can be calculated by dividing the viewing distance by three. Selecting a screen size based on this formula will result in a vertical viewing angle approximately equal to the recommended 18. Below are several charts listing the recommended display size depending on the seating distance. This formula can be reversed to recommend viewing distance. Simply multiply the height of the display screen by three to determine the ideal viewing distance. For some rooms, such as kitchens and bathrooms, smaller television sizes may be more appropriate because the purpose of the room is not centered on entertainment. Smaller display screens may be more suited for more single-purpose rooms, so these guidelines for selecting display size may not be universal. Screen Height Viewing Distance Figure 5: Calculating Display Size with Viewing Distance Screen Size Diagonal (in.) Screen Height (in.) Seating Distance (ft.) CEDIA

7 08 CONCLUSION While many believe bigger is better in the display world, it is important to understand how to select the appropriate screen size for the room. Ideally, the seating distance should be three times the height of the display to allow for a 33 horizontal viewing angle and an 18 vertical viewing angle for displays with 1080p resolution. The seating distance recommended allows the user viewing the screen to experience the immersion effect without losing detail in their peripheral vision, providing a more satisfying entertainment experience overall. Note: A useful tool for calculating the measurements of any display is the video calculator tool inside the CEDIA app. More information is available at cedia.net/app. 09 REFERENCES 1. Schneider, Joel (May 2002). Block Letter Eye Chart. International Society for the Enhancement of Eyesight. Retrieved from block_letter_eye_chart.pdf 2014 CEDIA 7