Re: Testability of Animation from interactions Issue 18

On 12/01/2017 21:28, Gregg C Vanderheiden wrote:
> Read my email, and WCAG glossary definitions.    I THINK all your
> questions are answered there.
> yes it did have standardized measures.
> No I don’t think it is questionable - because of the structure we
> used.    if you start at a point and set a criterion that is safe
> where all the variability goes toward more safe views.

So the most relevant part of the definition for me is the following:

"341 x 256 pixel rectangle anywhere on the displayed screen area when 
the content is viewed at 1024 x 768 pixels will provide a good estimate 
of a 10 degree visual field for standard screen sizes and viewing 
distances (e.g., 15-17 inch screen at 22-26 inches). (Higher resolutions 
displays showing the same rendering of the content yield smaller and 
safer images so it is lower resolutions that are used to define the 

So roughly, this equates to a rectangle that has the dimensions of 1/3 
of the width by 1/3 of the height of the viewport/screen.

What happens if any of the variables such as screen size or viewing 
distance change, but the rest remain the same? What if it's a 24 inch 
screen at same resolution and viewing distance? (not uncommon nowadays 
for people to have much larger screens, but to still sit at the same 
desk/distance from the screen)
It would result in a rectangle that has the same pixel dimensions, but 
actually in physical terms it's rendered larger, so occupies a larger 
field area in the user's absolute field of view.

So there is already variability here in real terms, and it's the same 
sort of variability that we're discussing here, no?

> the only thing not covered is if a person uses a magnifier on the
> flashing element.    But that will fail no matter what you do and the
> author can’t predict or address that anyway.

The author also can't predict the actual physical size of the screen, 
nor the actual viewer's distance. So there are assumptions being made 
(about the "standard screen size and viewing distance"), and with those 
fixed, the only other remaining variable is screen resolution (in the 
example in the spec, 1024x768). So, boiling this down, it seems 
reasonable to say that really the highly obscure definition of ".006 
steradians within any 10 degree visual field on the screen (25% of any 
10 degree visual field on the screen)" essentially comes down to (since 
2 variables have been assumed as ideal/fixed) "1/3 of the width by 1/3 
of the height of the viewport/screen". Or am I missing something?

>> Does the tool require you to enter the variables like physical
>> screen size, viewing distance, etc? Or does it simply base its
>> calculation on the screen/window size? If the latter, then it's
>> doing nothing different from what I'm proposing, i.e. anchoring any
>> measurement on viewport/screen size and writing out clearly what
>> that ratio is.’
> No,  If you read the whole email I think you will see that this is
> covered.

As above, the tool in that case assumes ideal/fixed conditions of 
physical screen size and viewing distance, I take it? So in essence 
simply calculates the ratio of the flashing area in relation to the 
whole screen size?

>> So the answer is actually yes? i.e. "visual field on the screen" as
>> a whole means the whole size of the viewport, and then of that you
>> calculate a 10 degree angle portion? If so, then it is possible to
>> rewrite the "10 degree visual field on the screen" into some
>> relationship that's anchored on the size of the viewport?
> No -  If you read it more carefully I think you will see why this is
> not true.  at least not how it is used in the  FLASH SC.

I have read it more carefully, but have come to the same effective 
conclusion...since physical screen size and viewer distance are assumed 
to be "ideal" (along the same effective ratio as having a 15-17 inch 
screen at 22-26 inches distance), it stands to reason that the ratio IS 
only calculated based on the area of what's flashing versus the overall 
screen area, no?

>>>>>> And if not, isn't the general flash/red flash definition
>>>>>> not also fundamentally flawed as it can't take into
>>>>>> account physical screen size / viewing distance / etc,
>>>>>> regardless of the existence of a "tool"?
>>> Not flawed.  But it is subject to the same problems you are
>>> talking about with this SC.   If you read the rest of the text
>>> of the glossary definition you will see we addressed them by
>>> assuming screen size, resolution, and viewing distance.  Since
>>> (in this case) we are talking about things being a problem if
>>> they are large— our assumptions were based on typical to older
>>> screens — with newer screens creating less of a problem.  So
>>> viewing the material on a higher resolution screen or on a mobile
>>> device would alway be safer.
>> But a mobile device screen is usually held closer to the viewer's
>> eye, which in essence means that it occupies the same/similar
>> overall visual field of a user as a larger monitor that's further
>> away, no?
> While that is true —  it is so much smaller that the distance
> difference is completely overwhelmed by the size difference — and the
> math still works out.   it is safer— so criteria is still met.

If I hold my mobile phone at 3-4 inches from my eyes (which for certain 
activities, like watching a movie, I just might), it occupies roughly 
the same area of my field of view as my 24" monitor on my desk at the 
average viewing I would not say that's always a safe bet.

>>> So our criteria resulted were based on research, were set to
>>> accommodate most common and older tech at the time, and still
>>> held (were safer) with newer and mobile screens.
>> I think this may need a rethink, or at least a different anchoring,
>> to make it more generally relevant in a world where screens come in
>> all shapes and sizes, resolutions, and typical viewing distances.
> The animation maybe - but the Photosensitive epilepsy provision still
> works even as we invent more shapes and sizes and resolutions of
> screens as long as we are viewing them at typical viewing distances
> for the different shapes sizes and resolutions

Both animation and photosensitive epilepsy are concerned with how much 
of the field of view the animation/flashing are taking up. So if, as 
discussed above, even for flash/red flash the measurement effectively 
boils down to a relationship of what's flashing in relation to the 
overall size of the screen (since we have to assume physical size and 
viewing distance are fixed/ideal since we can't guarantee nor measure 
them anyway), I'd say it's sensible to use the same rationale for 
animation and define this as a ratio of the viewport (not web page size, 
but actual visible viewport)...and after doing that also simplifying the 
definition for general flash/red flash the same way and removing the 
obscure ".006 steradians within any 10 degree visual field on the screen 
(25% of any 10 degree visual field on the screen)" measurement?

Patrick H. Lauke | |
twitter: @patrick_h_lauke | skype: patrick_h_lauke

Received on Thursday, 12 January 2017 23:00:13 UTC