The User Experience: Proper Image Size and Contrast

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Judith Lawson
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1 The User Experience: Proper Image Size and Contrast Presented by: Alan C. Brawn & Jonathan Brawn CTS, ISF, ISF-C, DSCE, DSDE, DSNE Principals Brawn Consulting

2 Proper Image Size The question of the proper image size versus viewing distance has been asked for over four decades in the audio visual industry. Up to this point in time there has not been an exact single formula that has undergone true scientific scrutiny. The variable is the viewing criteria for the application, and the fact that different viewing purposes will require different viewing distances, screen sizes and font sizes. For years, the commercial AV industry used a general rule, called the Rule. It simply stated that there are three viewing criteria, and a maximum viewing distance, based on screen height: Inspection viewing - 4X Screen Height Detailed viewing - 6X Screen Height General viewing - 8X Screen Height However, it has recently become understood that this, while originally functional, is a less accurate approach, and new standards have been developed to address this accurately.

3 Understanding Visual Acuity Starting with How We See

Visual Acuity Visual acuity is the sharpness of vision, measured by the ability to discern letters or numbers at a given distance according to a fixed standard eye chart.

4 Visual Acuity Visual acuity is the sharpness of vision, measured by the ability to discern letters or numbers at a given distance according to a fixed standard eye chart. Visual acuity is tested one eye at a time, with the help of a standardized Snellen eye chart. Visual acuity is a static measurement, meaning you are sitting still during the testing and the letters or numbers you are viewing also are stationary. Visual acuity also is tested under high contrast conditions typically, the letters or numbers on the eye chart are black, and the background of the chart is white.

Seeing in Degrees Human vision is not made up of pixels, like a digital display device. We see in degrees, based on our field of vision. From the top down, we consider a circle, 360 degrees.

5 Seeing in Degrees Human vision is not made up of pixels, like a digital display device. We see in degrees, based on our field of vision. From the top down, we consider a circle, 360 degrees. Each degree is split up into 60 parts, each part being 1/60 of a degree. These parts are called arc minutes (which can be further divided into 60 arc seconds). The angular measure of an object is expressed in degrees, arcminutes or arcseconds.

Seeing in Degrees Visual acuity accounts for human vision being measured in angles. Our vision subtends (or takes up) a certain number of degrees, which we call the field of vision.

6 Seeing in Degrees Visual acuity accounts for human vision being measured in angles. Our vision subtends (or takes up) a certain number of degrees, which we call the field of vision. This is true for both horizontal and vertical fields of vision. Our eyes both face forward (called binocular vision) and this cuts the circle in half, to 180. Due to anatomy and focus, we see clearly about 124, with approximately 2 in total focus. The remaining amount, which varies from individual to individual, is called peripheral vision.

7 Visual Acuity: Distinct Separation Visual acuity is the smallest object a human eye is capable of resolving, which is 1 minute of arc. However, the important aspect is to understand the shortest distance by which two lines can be separated and still be visualized as two lines. If two black lines (on a white background) are separated by a space subtending an angle of less than 1 minute of arc, then the two lines are not seen as separate, but fused together. When the visual angle between two lines is increased to 1 minute, the lines are seen separately.

Measuring Visual Acuity Visual acuity is typically measured using a Snellen eye chart. The Snellen eye chart is printed with eleven lines of block letters.

8 Measuring Visual Acuity Visual acuity is typically measured using a Snellen eye chart. The Snellen eye chart is printed with eleven lines of block letters. The first line consists of one very large letter, for example E, H, or N. Subsequent rows have increasing numbers of letters that decrease in size. A person taking the test covers one eye from 20 feet away, and reads aloud the letters of each row, beginning at the top. The smallest row that can be read accurately indicates the visual acuity in that specific eye.

9 Measuring Visual Acuity The 8 th line, designated 20/20, is the smallest line that a person with normal acuity can read at a distance of 20 feet. Three lines above, the letters have twice the height of those letters on the 20/20 line. If this is the smallest line a person can read, the person's acuity is 20/40, meaning that this person needs to approach to a distance of 20 feet to read letters that a person with normal acuity could read at 40 feet. In an even more approximate manner, this person could be said to have half the normal acuity of 20/20. The largest letter on an eye chart often represents an acuity of 20/200, the value that is considered "legally blind" in the US.

10 Measuring Visual Acuity The symbols on an acuity chart are formally known as optotypes. In the case of the traditional Snellen chart, the optotypes have the appearance of block letters, and are intended to be seen and read as letters. They are not, however, letters from any ordinary typographer's font. They have a particular, simple geometry in which: The thickness of the lines equals the thickness of the white spaces between lines and the thickness of the gap in the letter C The height and width of the optotype is five times the thickness of the line.

Measuring Visual Acuity Hermann Snellen (the creator of the Snellen eye chart) defined standard vision as the ability to recognize one of his optotypes when it

11 Measuring Visual Acuity Hermann Snellen (the creator of the Snellen eye chart) defined standard vision as the ability to recognize one of his optotypes when it subtended 5 minutes of arc. Thus the optotype can only be recognized if the person viewing it can discriminate a spatial pattern separated by a visual angle of 1 minute of arc.

Quality of Vision Although visual acuity testing determines the relative clarity of eyesight in standardized conditions, it isn't predictive of the quality of vision in all situations.

12 Quality of Vision Although visual acuity testing determines the relative clarity of eyesight in standardized conditions, it isn't predictive of the quality of vision in all situations. For example, it can't predict how well you would see: Objects similar in brightness to their background Colored objects Moving objects Three major physical and neurological factors determine visual acuity: How accurately the cornea and lens of the eye focus light onto the retina The sensitivity of the nerves in the retina and vision centers in the brain The ability of the brain to interpret information received from the eyes

13 Contrast and Visual Acuity

14 Visual Acuity and Contrast To human vision, contrast is the difference in luminance or color that makes an object distinguishable. In visual perception of the real world, contrast is determined by the difference in the color and brightness of the object and other objects within the same field of view. The human visual system is more sensitive to contrast than absolute luminance, we can perceive the world similarly regardless of the huge changes in illumination over the day or from place to place. If the contrast of an object is reduced, it may not be able to be perceived clearly, despite the viewer having excellent visual acuity. Limited contrast can reduce the amount of information that a viewer can perceive within an image. It is important to ensure an image on screen has proper contrast for human vision, along with ensuring it is the correct size for visual acuity.

15 Display Contrast Contrast is a measurement of an image, defined as the ratio of the luminosity of the brightest value (white) to that of the darkest value (black). Contrast is stated as the ratio between maximum and the minimum brightness values. e.g. 100:1 In display technologies, contrast is the difference between the luminance or brightness of an ON pixel and that of an OFF pixel. Off Pixel On Pixel Contrast Ratio = Luminance for ON Pixel Luminance for OFF Pixel Note: In real world applications, the way we perceive contrast is a function of the display, seating, ambient light, content, and even the color of the viewing environment.

16 The Effects of Contrast on Screen Low Contrast Image High Contrast Image Contrast is the element of a picture on a display that most notably drives the perception of quality in a picture. Contrast gives the effect of higher resolution by revealing detail and enhanced depth of field.

17 Display Contrast Measurements Intra-Frame (Sequential, Full On / Off) Contrast This measures the ratio of the light output of an all white image (full on) and the light output of an all black (full off) image. This measurement is used to demonstrate the maximum capabilities of a system in the environment in which it is installed.

18 Contrast Measurements Inter-frame (Checkerboard) Contrast This is measured with a pattern of 16 alternating black and white rectangles. The average light output from the white rectangles is divided by the average light output of the black rectangles to determine the contrast ratio. This measurement offers a more average measurement of system contrast ratio, under an approximation of all conditions the system might experience.

Contrast in the Real World With the high contrast specifications we see advertised today, it is important to

Black can only be as black as the display is under the ambient light present in the room.

19 Contrast in the Real World With the high contrast specifications we see advertised today, it is important to realize that the difference in performance between one display and another would only be apparent in a completely darkened room. The control of ambient light in a room is a critical issue when it comes to contrast performance. Black can only be as black as the display is under the ambient light present in the room. Hence, if the room is not pitch dark, the screen surface will reflect some light - thus turning black into dark gray, and therefore reducing image contrast ratio. This applies to all displays - most often, black is nothing more than dark gray!

Contrast Defined To better understand the impact of the presence of light in a room on the contrast ratio performance of an imaging device, we must understand the eye s reaction to light.

20 Contrast Defined To better understand the impact of the presence of light in a room on the contrast ratio performance of an imaging device, we must understand the eye s reaction to light. The human eye is capable of perceiving over 20 MILLION TO ONE contrast ratio, in the absence of ambient light. As ambient light increases, the eye reduces it s ability to perceive contrast. With the light emitted by just one candle in a room - that's just one lux the eye cannot perceive beyond a 500:1 contrast ratio. Increase the level of light in the room to just 30 lux - that's equivalent to a dimly lit room - and contrast ratios above 50:1 would turn out to be simply academic.

21 InfoComm Performance Standards System Contrast and Image Size

ANSI / InfoComm PISCR 3M-2011 The ANSI / InfoComm PISCR (Projected Image System Contrast Ratio) standard establishes the minimum amount of contrast required for a projected image system, taking into

22 ANSI / InfoComm PISCR 3M-2011 The ANSI / InfoComm PISCR (Projected Image System Contrast Ratio) standard establishes the minimum amount of contrast required for a projected image system, taking into consideration the projector light output, screen performance, and ambient light. All of this is done under the concept of system performance, and NOT the individual components since what we see is a combination of all elements of the system. PISCR is based on the fact that as display contrast is reduced, there is a measurable loss of information in the image shown. It consists of four viewing criteria, based on the purpose of using the system, and specifies a minimum contrast ratio for each.

23 PISCR Viewing Categories Informational Viewing (7:1) The viewer is able to recognize what the images are on a screen and can separate the text or the main image from the background under typical lighting for the viewing environment. There is passive engagement with the content (e.g., casual television viewing). Basic Decision Making (15:1) The viewer can make decisions from the displayed image. The decisions are not dependent on critical details within the image. The viewer is actively engaged with the content (e.g., photos, typical informational presentations, public transportation informational displays). Critical Decision Making (50:1) The viewer can make decisions from the displayed image based on critical details within the image. The viewer is fully engaged with these details of the content (e.g., architectural/engineering drawings, legal evidence, medical imaging and photography). Full Motion Video (80:1) The viewer is able to discern key elements present in the full motion video, including detail provided by the cinematographer or videographer necessary to support their story line and intent (e.g., home theatre).

25 ANSI / InfoComm DISCAS V202.01:2016 InfoComm has published a new standard to set specifications for screen sizing based on viewing distance. It is called Display Image Size for 2D Content in Audiovisual Systems (DISCAS). The goal of DISCAS is to create a scientific standard, based on human vision, to define the screen size for a given audiovisual system based on audience viewing distance and purpose of the system. To define the maximum viewing distance, DISCAS is based on two viewing categories, for how the system will be utilized. Size Matters!

The Purpose of DISCAS This Standard provides measurement and reporting methodologies for the assessment, documentation, and categorization of new and existing audiovisual

The Standard provides a calculation/assessment tool for determining proper display image size based upon viewer needs as defined under two viewing categories.

26 The Purpose of DISCAS This Standard provides measurement and reporting methodologies for the assessment, documentation, and categorization of new and existing audiovisual systems. The Standard will assist professionals engaged in the design of audiovisual systems determine appropriate displayed image sizes. The Standard provides a calculation/assessment tool for determining proper display image size based upon viewer needs as defined under two viewing categories. When planning a display, audiovisual designers often encounter limitations with dimensions and layout in relation to optimal displayed image size. This Standard provides formulas to design and display suitable content.

27 The Purpose of DISCAS This Standard can be used to: Plan and design new displayed image systems Determine image size relative to space and viewing requirements Determine Closest and Farthest Viewer Positions Determine horizontal angles of view Provide metrics for content design

Using DISCAS Essentially, DISCAS allows a user to specify an image size, based on the closest and farthest

DISCAS can also be used to specify a farthest and closest viewing distance based on image height.

visual acuity. For this seminar, we will focus on specifying proper image size based on viewing distance.

28 Using DISCAS Essentially, DISCAS allows a user to specify an image size, based on the closest and farthest viewing distances for a given environment. DISCAS can also be used to specify a farthest and closest viewing distance based on image height. DISCAS takes into account content by using the size of content elements on screen, and taking into account human visual acuity. For this seminar, we will focus on specifying proper image size based on viewing distance. This is done by measuring the space, then selecting the proper application (Viewing Category) that the system will be used for. This will guide us through the proper formulae to use to calculate image size.

29 DISCAS Viewing Categories Analytical Decision Making The viewer is fully engaged with minute detail present in the content and needs to be able to resolve every element of the displayed image. Analytical decision-making environments support critical assessments, including but not limited to examination of medical imaging, fine arts, engineering or architectural drawings, electrical schematics, photographic image inspection, forensic evidence, or failure analysis. Basic Decision Making The viewer can make basic decisions based on the displayed image. The decisions are not dependent on critical details within the image, but the viewer can assimilate and retain information. The viewer is actively engaged with the content (e.g., information displays, presentations containing detailed images, classrooms, boardrooms multi-purpose rooms, product illustrations). Graphic images and text are legible to the extent that the viewer can make decisions based on what is being seen. Decisions are made by comprehending the informational content itself and are not dependent on the resolution of every element of detail System design criteria may include one or both of these viewing categories based on the needs of the viewer.

30 Basic Decision Making If only Basic Decision Making is selected, the following variables are used: %Element Height Basic Decision Making (BDM) incorporates consideration of image content, specifically element height, the prime example being font size. The BDM %Element Height factor represents the ratio of element height to screen height expressed as a percentage (e.g., 1.0% represents an element height of 1 unit relative to 100 units screen height). BDM Acuity Factor (200) This variable relates to visual acuity, specifically 20/20 vision, and provides the user with an easy-to-use method to relate perceived Element Height relative to viewing distance by providing an alternative to the trigonometric calculations otherwise required.

31 Basic Decision Making To determine minimum Image Height, the formula is: IH= FV 200 x %EH Where: IH is the minimum Image Height for the space FV is the farthest distance a viewer will be from the image %EH is the Element Height, which is the height of the element being viewed expressed as a percentage of overall image height 200 is the Acuity Factor for Basic Decision Making Note that the display shall have sufficient resolution to render an element at its smallest prescribed size. Farthest Viewer Distance shall be determined either by physical measurement in an existing space or from the architectural layouts.

32 Basic Decision Making Calculating % Element Height: Font size Font size in points can be converted to pixels, and then that pixel value can be calculated as a percentage of overall specified vertical resolution. Graphic size Graphic height in pixels can also be used to calculate a percentage of specified vertical resolution. You can also estimate or measure the percentage of image height that any object on screen will occupy. Any of these three approaches can supply the % Element Height for calculating screen size. For example, 16 point font on a PowerPoint slide (like this one) will be 22 pixels tall. This is 2% of image height.

Analytical Decision Making If only Analytical Decision Making is selected, the following variables are used: ADM Acuity Factor (3438) This factor relates to visual acuity, specifically 20/20 vision,

33 Analytical Decision Making If only Analytical Decision Making is selected, the following variables are used: ADM Acuity Factor (3438) This factor relates to visual acuity, specifically 20/20 vision, and provides the user with an easy-to-use method to relate image resolution (pixel height) relative to viewing distance by providing an alternative to the trigonometric calculations otherwise required. Vertical Image Resolution (e.g., 1080)

34 Analytical Decision Making To determine minimum Image Height, the formula is: IH= IR x FV 3438 Where: IH is the minimum Image Height for the space IR is the vertical image resolution FV is the farthest distance a viewer will be from the image 3438 is the Acuity Factor for Analytical Decision Making Farthest Viewer Distance shall be determined either by physical measurement in an existing space or from the architectural layouts.

35 Both ADM and BDM If Basic Decision Making (BDM) AND Analytical Decision Making (ADM) are BOTH selected: When viewing requirements dictate use of both BDM and ADM, the image size and viewing distances shall be determined by the ADM formulas Once these calculations have been made, the user shall calculate the %Element Height and Closest Viewer boundaries Users will note that in the case of high resolution displays selected for enhanced viewing requirements of ADM, it is theoretically possible to display elements (e.g., fonts) of impractically small size relative to viewer needs. Therefore, it is necessary to calculate the %Element Height appropriate for the display image size chosen for ADM viewing needs.

36 Practical Usage of DISCAS System Example

37 DISCAS Example System To help you understand DISCAS further, let s use it for a hypothetical conference room we will design. We know how large the room is, and where the farthest viewer will be, based on architectural drawings. This will let us know how large a display we should specify for the environment. Of course, we all understand the limits of customer budgets, and how that might challenge our specification, but DISCAS allows us to point to an ANSI Standard that demonstrates why we need a screen that large. You might be surprised at how much larger the image needs to be, compared to what you might have estimated!

38 DISCAS Example System

39 DISCAS Example System Let s presume this room is going to be used for viewing detailed spreadsheets or technical diagrams, thus it would fall under Analytical Decision Making. The proposed display will be 1080P in resolution, due to budget concerns. This means that we know our vertical resolution to be We also know the farthest viewer is 22 away from the wall where the display will be installed. The formula is Image Height equals Image Resolution times the Farthest Viewer, then divided by the ADM acuity factor of This means our screen must be at least 6.91 high for proper viewing. This is 14.1 diagonal for 16:9! 6.91= 1080 x

40 DISCAS Example System Let s examine the same room being used to view normal PowerPoint presentations. This would fall under Basic Decision Making. The proposed display will be 1080P in resolution, due to budget concerns. This means that we know our vertical resolution to be We also know the farthest viewer is 22 away from the wall where the display will be installed. The formula is Image Height equals Farthest Viewer divided by the ADM acuity factor of 200, multiplied by the % Element Height. To calculate % Element Height, take the smallest common font size (or other content element size), and calculate its height in pixels as a % of the vertical resolution of the display. IH= FV 200 x %EH

41 DISCAS Example System In our room, we have a Farthest Viewer of 22, and we will propose that our PowerPoint presentations will standardize on a 16PT font. 16PT font converts to 22 pixels. 22 pixels is 2% of 1080 (our vertical resolution). 2% of 200 is 4, 22 divided by 4 equals 5.5. This means our screen must be at least 5.5 high for proper viewing. This is 11.2 diagonal for 16:9! IH= FV 200 x %EH

42 DISCAS Example System This means that the screen should actually be quite a bit larger than expected. In this room, under ADM, the screen would need to be 14.1 diagonal (approximately 169 ). To use this room for BDM, assuming 2% Element Height, the screen would need to be 11.2 (approximately 134 ). To relate this to everyday use, the largest single flat panel commonly available is 98 diagonal. Assuming 1080P, and the same criteria from above, the farthest viewer can only be: ADM BDM 16 Just remember, we can t break the laws of physics, and human visual acuity!

Brawn, CTS, ISF, ISF-C, DSCE, DSDE, DSNE

45 For More Information If you would like more information, please contact Brawn Consulting and the Digital Signage Experts Group: Alan C. Brawn, CTS, ISF, ISF-C, DSCE, DSDE, DSNE Jonathan Brawn, CTS, ISF, ISF-C, DSCE, DSDE, DSNE Dave Haar, DSCE, DCME

4K Resolution, Demystified!

4K Resolution, Demystified! Presented by: Alan C. Brawn & Jonathan Brawn CTS, ISF, ISF-C, DSCE, DSDE, DSNE Principals of Brawn Consulting alan@brawnconsulting.com jonathan@brawnconsulting.com Sponsored