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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: filling area by color atack safety
Date: Tue, 19 Mar 2024 21:19:19 -0700
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Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:

> On 19/03/2024 05:54, Tim Rentsch wrote:
>
>> Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
>>
>>> On 18/03/2024 09:30, Tim Rentsch wrote:
>>>
>>>> Michael S <already5chosen@yahoo.com> writes:
>>
>> [...]
>>
>>>>> Except I don't understand why it works it all.
>>>>> Can't fill area have sub-areas that only connected through
>>>>> diagonal?
>>>>
>>>> It is customary in raster graphics to count pixels as adjacent
>>>> only if they share an edge, not if they just share a corner.
>>>> Usually that gives better results;  the exceptions tend to need
>>>> special handling anyway and not just connecting through
>>>> diagonals.
>>>
>>> Though with a binary image, if the foreground is 4-connected, the
>>> background must therefore be 8-connected.
>>
>> It might be but it doesn't have to be.
>>
>> Also different terminology should be used, since 4-connected
>> (also N-connected, for other integer N) has a specific meaning in
>> graph theory, and one very different than what is meant above.
>
> That is the terminology in binary image processing.  The pixels are
> 4-connected or 8-connected depending on whether a shared corner is
> considered to make the group of pixels two objects or one object.

A poor choice of terminology.  Side adjacent or corner and side
adjacent would be better.