Sampling a random set of pixels. about libvips

[jcupitt]

Hi @atandamen,

For smallish images, probably the simplest thing would be to render to a big array and then just pick pixels randomly.

For large images, I think I would do something like what you suggest -- make a noise image and mask it. You can use max to find the top $n points and their values. I think it's only been tuned for small values of n though, so it'd probably perform poorly for large numbers of pixels.

Your final option would probably be to make a new libvips operation that sampled points. That'd need good C/C++ though.

[jcupitt]

So eg.:

$ vips max k2.jpg --size 10 --x-array --y-array
634 658 659 660 1022 1023 1024 1025 1026 1027 
1280 1280 1280 1280 1280 1280 1280 1280 1280 1280 
255.000000

So the three lines are the x and y coordinates of the top 10 points, and the top value (255). The C# interface is the same.

[atandamen]

Yes, that seems to be enough.