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AFB  ®
Technology News for People Who Are Blind or Visually Impaired
From the American Foundation for the Blind
 November 2009 Issue  Volume 10  Number 6

Access Issues

Screening Displays for Low Vision Access: A Look at Popular Audio Players and Book Readers

Products of all types now seem to have an embedded small visual display interface that creates a significant accessibility barrier (and opportunity) for people with vision loss. These displays are everywhere--on cell phones, digital watches and clocks, calculators, household appliances, home medical devices, such as blood pressure monitors, point-of-sale devices at store checkouts, bank ATMs, digital cameras, and exercise equipment, to name a few. These displays often have small fonts, poor contrast, glare, flashing or moving text, and colors that can be difficult to see, creating accessibility barriers to people who have low vision. Additionally, technology developers are dramatically shrinking the size of handheld devices and home electronics, using very small displays, resulting in condensed text and information.

AFB TECH recently examined several characteristics of small visual displays embedded in popular digital audio players and e-book readers, including: font size and type, the display's contrast level, and the resolution of the screen.

The readability of these small visual displays varies greatly from product to product, due to the display's quality. Higher quality displays most often exhibit brighter and more easily readable text. However, aside from display quality, display characteristics chosen by manufacturers, such as font size and type, and colors and display styles used, are also major factors affecting readability. For people with low vision, when comparing the readability of small visual displays and selecting products to purchase, it is important to consider all these factors.

This problem is made more severe, because manufacturers of small displays, unlike manufacturers of large displays such as computer monitors and televisions, do not have an industrial standard for display characteristics. This means there is no agreement among manufacturers about font size, color choice, display technology, or overall quality of the display used. As a result, readability can vary wildly between devices.

Last July, we published the article entitled, "Combating the Small Visual Display Invasion: AFB Works to Set a Display Quality Standard," in which AccessWorld readers learned of AFB TECH's initiatives to set a quality standard for small visual displays (SVDs). AFB TECH has received a grant from the National Institute on Disability and Rehabilitation Research, to develop standards for small visual displays. As part of this project, AFB TECH has been working with the Rehabilitation Research & Development Center of Excellence at the Atlanta VA Medical Center, to validate a contrast standard to improve the overall accessibility of small visual displays for people with low vision.

Before looking at specific products, we provide this explanation of display measurements, as well as information explaining how we obtained them and why they are important for people with low vision.

Contrast

Contrast is perhaps the most important characteristic determining readability of a small visual display. For a display to be easily read there needs to be a clear separation between the text and its background. Many lower-quality displays use dark text on a grayish or non-white background, which can make it very difficult to read. To facilitate high contrast, a display must be capable of displaying both very dark characters and very bright backgrounds, or vice-versa for those who see reverse polarity best.

Even high-quality displays can exhibit poor contrast through color choices made in the menu screens. If manufacturers choose a color scheme other than white and black for their devices, such as black-on-blue or white-on-gray, this can decrease the level of contrast. When taking contrast measurements, AFB TECH examines the contrast between the text and its background for the main screens in each of the devices and calculates a percentage value for its contrast. Contrast for small visual displays can range from around 30% (very poor) to 95% (very good).

Font Size and Type

Font size is a major issue for small visual displays, because the limited display size often leads to small and crowded text. For printed text, the American Printing House for the Blind recommends a minimum of 18 point font, which in Arial is 4.5 mm, but for many of these small visual displays the font can be as small as 1.7 mm. Even the largest default fonts are rarely larger than 3 mm, which can be a serious problem for people with low vision.

Additionally, the font style used can have a significant effect on readability. There are two basic font styles: serif and sans-serif. Serif fonts, such as Times New Roman, use fine lines to add detail to characters, but this can have the effect of making the text thinner and more difficult to read. Sans-serif fonts are usually simpler in style and easier to read, thus are better for people with low-vision. In our measurements, we determine both the size and style of the fonts used for the menu screens in each of the devices.

Resolution/PPI

All the small visual displays evaluated in this article are composed of thousands of tiny pixels that are used to create the images and text displayed. The more pixels a display has, the more detail it is capable of producing. Displays with fewer pixels are less capable of rendering detail, which often results in "blocky" shaped characters that are more difficult to read.

There are two ways to measure the amount of pixels on a screen. One method is resolution, a count of the total number of pixels horizontally and vertically in a display. For example, a display with a resolution of 320 x 240 would have 320 pixels horizontally and 240 pixels vertically. The resolution of small visual displays can vary from approximately 96 x 32 (low) to 800 x 600 (high).

A similar measurement to resolution is pixels per inch (PPI) which, as the name suggests, measures the number of pixels per inch of display diagonally. This, unlike resolution, is not related to the size of the display but reflects how sharply the screen can display images and text in a given area. This measurement is provided as a single number, and for small visual displays, it can range from around 30 (low) to 200 (high).

How do the Products Measure Up?

We compared display measurements of the Sansa Fuze, Microsoft Zune, iPod Classic, iPod Nano, iPhone, Sony eBook Touch Reader, and the Amazon Kindle.

The Sansa Fuze's main menu has a contrast of 88.14%, while its submenu has a contrast of 89.4%. It has a display resolution of 220 x 176, and a font size of 1.9mm.

The Microsoft Zune has a contrast measurement of 91.06% on its display, but when a menu item is selected the contrast drops to 59.68% making it actually more difficult to see than the other choices in the menu. Its display resolution is 320 x 240, and the maximum font size in its main menu is a very large 8.5 mm and has a minimum font size of 2.0 mm.

The iPod Classic has a display contrast of 91.44% and a resolution of 320 x 240. The font on its display measures 1.85mm.

The iPod Nano has a display contrast of 91.50%, and a display resolution of 320 x 240. It has a maximum font size of 1.90mm and a minimum font size of 1.71mm.

The iPhone has the highest contrast of any display we have measured to date with a 96.12% contrast and a display resolution of 320 x 480. It has a maximum font size of 3.89mm and a minimum font size of 1.87mm.

The Sony eBook Touch Reader used for reading electronic books has a display contrast of 41.7% which is notably lower than the previously listed devices. It has a display resolution of 800 x 600, with a maximum font size of 5.94mm and a minimum font size of 1.96mm.

Lastly, the Amazon Kindle has the lowest display contrast we have measured to date, with a 30.08% contrast measurement. Its display resolution is 600x 800; its maximum font size is 3.79mm, and its minimum font size is 1.80mm.

Because of the amount of variance in font size, contrast, and resolution in these displays, it is difficult to specify which display is the most accessible for people with low vision. Some devices, such as the iPod Nano, use high contrast with small fonts. Other devices, like the Microsoft Zune, have large characters with fairly poor contrast. Additionally, the two book readers, the Amazon Kindle and the Sony eBook Touch Reader, have a type of display that allows for large and adjustable font, but use a black-on-gray color scheme that has very poor contrast.

If you have difficulty reading small text in these types of devices, then the minimum font size for each of these digital audio players should be more important to you than the maximum font size; for a screen like the Zune, although the main menu has a very large 8.0mm size font, all submenus and text are much smaller. Likewise, for contrast values, some of these devices have differing levels of contrast, and the lowest level is what will likely cause the most problems when using it. Resolution, although important when comparing the amount of detail a display is capable of producing, does not have as large effect on low vision accessibility as contrast or font size. When purchasing a digital audio player or any product with a visual display, it is important to consider how important contrast, font size, and resolution are to your reading experience.

All of these characteristics combine to form a set of potential problems for consumers as well as manufacturers. AFB TECH hopes to measure as many small visual displays as possible, and make the data available for the benefit of people with low vision. As AFB TECH continues to expand its optics lab, we hope to measure more display characteristics, such as glare, and present the findings to industry, in order to make products more accessible to people with vision loss.

Sidebar for "Screening Displays for Low Vision Access"

How Measurements Were Taken

AFB TECH's custom-designed optics lab consists of four separate parts:

  • A platform to secure the device
  • A light source that shines a controlled level of light onto the small visual display
  • A digital camera which takes a precise image of the display
  • A dedicated computer which analyzes the display's image

As stated previously, contrast is the most critical measurement determining a display's readability. To calculate its value, we use a computer program developed in cooperation with Marshall University researchers and interns. This program takes the image of the display and calculates its contrast.

Information on a device's display resolution and PPI can often be found in its user manual or spec sheet. If that information is not available, we can determine the resolution by taking a picture of the entire display and counting its pixels horizontally and vertically. PPI is calculated through a formula using the vertical and horizontal size and pixel count of the display.

To determine font size, a reticle, which is a piece of glass with a very fine ruler printed on it, is placed on top of the display being measured. An image of the display is then taken with the reticle attached. That image is then viewed on a full-size monitor, so the font height can be precisely measured. Since font size can differ on a device from menu to menu, measurements for every menu on the devices were taken. Determining if the font is serif or sans serif is simply a matter of examining the letters to see if they have embellishments.

Why These Measurements are Important

Since SVDs can be found everywhere in this new digital era, it is becoming less of an option to find ways around seeing the display. Touch screen displays, for example, can be completely inaccessible to a person who does not have sufficient vision to read them. Fortunately for users of digital audio players, there are still options for those who are not able to read the displays including voice output and models that operate completely without a display. For people with low vision and who have the potential to read a display, contrast, font size, font style, resolution, and PPI all play a part in determining readability of a display.

Future Plans

The AFB TECH Optics Lab is under constant development to measure as many visual characteristics of small displays as possible. The lab is currently capable of taking measurements of contrast, font size, font style, and resolution/PPI, but work is being made to include measurements for other characteristics as well, including reflection. Reflection measures how reflective a display is and the amount of glare it gives off under normal lighting conditions. This has been found to be a major cause of inaccessibility for people with low vision, and will be part of the AFB TECH Optics Lab in the near future.

The goal of AFB TECH's optics lab is to take measurements of a wide range of devices with small displays, and use that information to create a user-friendly and accessible database to be posted on AFB TECH's website. This database will list the display measurements of hundreds of products, so consumers and manufacturers can determine which SVDs provide the best accessibility for low vision users. The completed database will also offer instructions and explanations on how to interpret the data, with easy-to-understand examples. This way, people with vision loss will be able to use the database to determine how accessible a particular display will be for them, based on its usability and the quality of its display.

Additionally, the database will be made available to manufacturers of SVDs, allowing these companies to gauge the accessibility of their displays against their competition. By providing detailed technical data to the manufacturers, it will be possible for them to determine the aspects that contribute to SVD accessibility and will hopefully encourage companies to make their displays readable to a larger population.

Related Articles

Combating the Small Visual Display Invasion: AFB Works to Set a Display Quality Standard by Lee Huffman


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Copyright © 2009 American Foundation for the Blind. All rights reserved. AccessWorld is a trademark of the American Foundation for the Blind.

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