Subject: Re: Antialiasing
From: [email-masked] (Jim McCabe)
To: [email-masked]
Date: Wed, 14 Sep 1994 12:21:20 -0700

>> Turning Adaptive Sampling OFF is almost the same as
>> leaving it ON and setting the Threshold to 0.

Mark Thompson replies:

>
>However, I think its important to understand that they are NOT the same.
>With adaptive on, you only have 1x spatial sampling until an edge is detected.
>Then it uses 5x, 9x, or 17x depending on your AA setting. But even with the
>adaptive threshold set to 0, it can miss edges because of the 1x sample for
>edge detect. What this means is, if you have a very fine pattern in your image,
>using adative (regardless of the threshold value) can cause "dropouts"  or
>breaks in the pattern. With adaptive off, those dropouts are 5 to 17 times
>less likely to occur (depending on AA). BTW, both motion blur and depth of
>field disable adaptive edge detection.

Boy, this guy is good !! After reading it a few times, I think I understand 
that when you select Adaptive Sampling (at ANY threshold) it only checks for 
edges once; if you turn it off totally, it checks multiple times (5 to 17, 
depending upon whether you have AA set for Low, Medium, or High). With 
Adaptive on at any threshold, since it only checks once, it may miss some 
fine edges, resulting in some non-AA'd "dropouts". Is that a fair paraphrase 
? I'm surprised that detecting edges is a hit-or-miss deal. Does it check 
different color contents on subsequent passes ?