pcb blinking diff

[Bert Timmerman]

The current pcbdiff tool uses the colours red and blue to mark the differences between two pcb files of the same sizes (width and length).

Elements common to both pcbs are presented in grey shades.

The colours red and blue can make it difficult, if not impossible, for people impaired with a colour vision deficiency (red/green, blue/yellow or total) to distinguish the differences between the pcbs, thus rendering the tool less usable.

By alternating showing the first and second pcb ("blinking") in grey shades, the differences between both pcbs can be seen without colours or the ability to perceive colour.

[Bert Timmerman (bert-timmerman)]

Please test this patch.

Kind regards,

Bert Timmerman.

[Bert Timmerman (bert-timmerman)]

Hi,

I incorporated the pcb_blink script into pcbdiff.

Activated by a third parameter (delay) on the command line.

Please test and any feedback is welcome.

Kind regards,

Bert Timmerman.

[Bob Paddock (bob-paddock)]

> The current pcbdiff tool uses the colours red and blue to mark the
> differences between two pcb files of the same sizes (width and
> length).
>
> Elements common to both pcbs are presented in grey shades.
>
> The colours red and blue can make it difficult, if not impossible, for
> people impaired with a colour vision deficiency (red/green,
> blue/yellow or total) to distinguish the differences between the pcbs,
> thus rendering the tool less usable.
>
> By alternating showing the first and second pcb ("blinking")

Personally I like blink, as I always have a hard time with colors like
good on this monitor, however
if the person is prone to eye problem they, and others, could be prone
to Photosensitive Epilepsy,
which is something to be aware of when 'blinking' screens or LEDs.

http://www.softwaresafety.net/Epilepsy/index.html has some of the
research I've done on this:

==================================================================
These quotes come from the website of the British Epilepsy Association:

http://www.epilepsy.org.uk/info/photofrm.html:
- "It should be bore in mind that people with photosensitive epilepsy
are unlikely to be troubled by a flicker rate of under five per
second"
- "Only 50% of photosensitive people are sensitive to 50Hz but 75% are
sensitive to 25Hz"
- "100Hz television sets will almost entirely solve the problem"

This quote comes from the website of the National Society for Epilepsy (UK):

http://www.epilepsynse.org.uk/pages/info/leaflets/photo.cfm:
- "The frequency of flashing light which is most likely to provoke
seizures varies from person to person. Generally, it is between the
frequencies of 5-30 flashes per second (hertz). Some people, however,
are photosensitive at higher flash frequencies. It is uncommon to have
photosensitivity below 5 hertz."

Avoid LED blinking or modulation at rates between 5 and 100Hz.
==================================================================

--
http://blog.softwaresafety.net/
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[Bert Timmerman (bert-timmerman)]

Hi Bob,

Thanks for the warning.

The default delay value is 50, which means 50 centi-seconds, which equals to toggling every 0.5 seconds, which gives 2 Hz.

On my laptop it takes even longer than 0.5 seconds for the default value to toggle (twice a second).

The above UK site mentions:
<quote>
Most people with photosensitive epilepsy are sensitive to 16-25 Hz. Some people may be sensitive to rates as low as 3 Hz and as high as 60 Hz.
</quote>

Nevertheless the user can still inflict some damage upon him/herself by changing the delay parameter, or tuning/modifying the software, their computer, or whatever.

My gut feeling (legal advisor) says it's better to withdraw any patch for any blinking whatsoever, due to the way the US legal system regarding injuries and lawsuits functions.

Bear in mind that the upstream pcb repository resides on US soil.

3 Hz is just to close to 2 Hz for me to feel comfortable.

Put in other words: risk = probability * effect --> I take zero chance and rather have no effect.

Kind regards,

Bert Timmerman.

[Bob Paddock (bob-paddock)]

> My gut feeling (legal advisor) says it's better to withdraw any patch

Sorry to hear that.

> for any blinking whatsoever, due to the way the US legal system
> regarding injuries and lawsuits functions.

It is a shame that we must live our lives in fear of lawyers...

> Put in other words: risk = probability * effect --> I take zero chance
> and rather have no effect.