Food for serious thought.

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Food for serious thought.

Wayne Dick-3

Practicality of Very Large Print and a Responsive User Interface for People with Low Vision

A lot of literature places a cap of approximately 200% on the practical magnification size for large print.  Larger than that and many contend that extreme methods like changing to Braille or use of screen magnification are the only possible solutions. For example, "Students who need print 28 points or larger should probably be considered as candidates for Braille education.", American Printing House for the Blind).  This set of calculations shows that a very satisfying reading experience can be obtained with up to 900% enlargement of 12 point font when normal word wrapping is employed.  Since word wrapping is one of the oldest technologies of the personal computing and web era, the technology to obtain this user interface is well known and well within the means of any web author, media producer or browser provider.

For many people with low vision it is very possible to read on a laptop with a standard screen of 13.3 inches. Now a good print size for normal readers is 12 point, where we use the Adobe standard point size of 1/72 inch.  Thus 24 point is 200% normal, 36 point is 300% normal, 48 is 400% normal, 72 point is 600% normal and 108 point is 900% times normal.  This range should be sufficient to address the needs of people with mild low vision (20/40-20/60) and moderate low vision (worse than 20/60 and better than 20/200).
Now the list bellow gives the screen capacity in characters. This is calculated as follows: If we break the screen into an grid where each grid square has an edge size in points: 24, 36,...108. Now for line length there are between 2 and 2.4 characters per square due to proportional packing and character widths that are less than the actual square height. The line height just equals the square height. Using 2.2 as the width multiplier and rounding off fractional parts we get the following.

  • 13.3" monitor
    • 24 pt = 1/3 inch letters has 76 character lines and 19 lines per page.
    • 36 pt = 1/2 inch letters has 50 character lines and 13 lines per page.
    • 48 pt = 2/3 inch letters has 38 character lines and 9 lines per page.
    • 72 pt = 1 inch letters 25 character lines and 6 lines per page.
    • 108 pt = 1.5 inch letters 16 character lines and 4 lines per page.

For less visual acuity, a non-portable solution using 20-36 inch monitors would include approximately the same screen capacities with nearly double the magnification. Note that 16 characters per line would involve some horizontal scrolling for words larger than 16 characters.  That would be very infrequent in most languages.

If people with low vision were given a responsive interface, whether it is obtained by a popular authoring technique like responsive web design (RWD) or by some other means, they can benefit. The only real responsiveness required is reversion to one column format with appropriate print size. In the intermediate ranges 36 point to 72 point, use of a portable device like a 13.3 inch laptop as a reading device is extremely practical. 
Not everyone with low vision needs large print. For this group, line length is often an issue. Again a single column format with narrow columns may work, or a multi-column format depending on the user's need.

The main point is this. Responsive user interfaces are old in the world of personal computing and the technology is well know. The first was automatic word wrapping and WYSIWYG. That sold personal computing to the general public.  It was followed by early Microsoft Windows systems that enabled the user's choice of icon and font size, color and font face that propagated through all Windows applications.  This was lost with Windows 7 and later, but the capability was established.  Any entity who cared to put in a little effort could establish responsive user interfaces that would work for people with low vision.  This article demonstrates that for most people with low vision, there is even a portable solution. No new technology needs to be invented. All that is needed is a user interface that is built with responsiveness in mind.

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Re: Food for serious thought.

Felix Miata-2
Wayne Dick composed on 2015-09-07 11:49 (UTC-0700):

> All that is needed is a user interface
> that is built with responsiveness in mind.

When it comes right down to it, all that's really required is to embrace the
user's choice of text size, whatever sizes those may be. That means not using
px units for sizing anything remotely related to text; to make the user's em
unit the unequivocal and immutable baseline for text and text container sizing.

The proof is in the result from user disabling author styles, such as
Firefox's View -> Page Style -> No Style. Dominant text size then becomes the
user's optimal, with other sizes determined by semantics and the user agent's
style sheet. IOW, responsiveness is restored to automatic with styles disabled.

The resulting problems follow from disabled author styles related to colors,
and positioning that's inconsistent with logical semantic structure. But
these pale in comparison to the fundamental need to be able to read text. Few
pages can serve any purpose if their text content isn't sufficiently legible.

Pages styling text using px units aren't designed for users, they're designed
for designers, to be looked at as if graphical images, not utilized for
whatever text content they provide.

The px unit needs to be stripped from all CSS contexts except those
exclusively related to bitmap images. It was wrong to ever have included px
unit applicability to sizing web text with CSS.
"The wise are known for their understanding, and pleasant
words are persuasive." Proverbs 16:21 (New Living Translation)

 Team OS/2 ** Reg. Linux User #211409 ** a11y rocks!

Felix Miata  ***