[postgis-users] Pixels' neighbors

[Hugues François]

Hello,

Given a one band raster made of numerous tiles and a point geometry from which I select one pixel, I would like to compare its value with its (8) neighbors' values. For now I do that with st_value(rast, geom) and playing with point coordinates (x +/- pixel width and y +/- height) : it works fine but it is very slow and I have to make a loop to compare selected pixels' values with their neighbors until I reach a certain value.

What I would like is to do all that only with raster but I don't see how to compare one pixel value with its neighbors (within the same tile or into a  neighbor tile). I assume I miss something and this is obvious for some of you, so if you could give a hand, i would be sincerely grateful.

Regards,

Hugues.