First:
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Without preload:
876600 pixels in 70.655ms = 12.407Mpix/s or 47.33MB/s
With preload:
876600 pixels in 69.953ms = 12.531Mpix/s or 47.80MB/s
Now:
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Without preload:
876600 pixels in 60ms = 14.610Mpix/s or 55.73MB/s
With preload:
876600 pixels in 49ms = 17.890Mpix/s or 68.24MB/s