Why is the AsImage(DX11.Texture2D) in image pack works so slowly?

vvvv beta question
1

If i create a new patch and use cv.image to find contours, the AsImage node spends 1210 time(I don’t know the unit…)
https://vvvv.org/sites/default/files/imagecache/large/images/Unnamed%20QQ%20Screenshot20150714161518.png

but if I add this patch to my project, the AsImage node spends 23000 time
https://vvvv.org/sites/default/files/imagecache/large/images/Unnamed%20QQ%20Screenshot20150714162441.png

Why is this and how can I make it run faster?(vvvv beta33.7)

2

asImage has to get the bitmap data from the gpu domain back to the cpu domain which is a quite costly operation.