In case it turns out to be difficult to set the context_rect to be variable (set on an output pixel by pixel basis--Eric is looking into this), I'd like to know what I could assume is the largest reasonable downsampling ratio, meaning that larger downsampling ratios would be clamped down to this ceiling. Such clamping would allow us to set the context rectangle to a (reasonably small) fixed value.

More specifically, could I reasonably clamp the downsampling ratio (in each direction) to one of the following values?

1.0 (context_rect.width = 4) 2.7182818284 (context_rect.width = 5) 7.3890560989 (context_rect.width = 6) 20.0855369231 (context_rect.width = 7) 54.5981500331
148.4131591025
403.4287934927
1096.6331584284
2980.9579870417 (context_rect.width = 12)

(first and last ones included for the sake of completeness.)

The smaller the maximum, the faster the code will run.

(As the above table makes pretty obvious, the method will be more suitable for mild downsampling that "heavy duty.")

Nicolas Robidoux Universite Laurentienne

Adam Turcotte has communicated to me that he is pretty sure that context_rect can be changed dynamically. Consequently, this thread is obsolete (unless changing context_rect dynamically leads to a high speed penalty), because the largest context_rect for the suggested method is not so large so as to "stick out" of the fetch_rectangle.

Nicolas Robidoux