Feeding the upper image to the code below and running it as a vulkan compute shader produces the bottom image
Source Code:
kernel [1,1,1]
fn main(input_image: image2d, size: int) -> (output_image: image2d)
{
int2 image_size = get_image_size(input_image);
int width = image_size.x;
int height = image_size.y;
uint2 coord = [ get_global_id(0), get_global_id(1) ];
float4 sum = 0;
uint num = 0;
int2 shift = 0;
for (shift.x = -size; shift.x <= size; ++shift.x) {
for (shift.y = -size; shift.y <= size; ++shift.y) {
int2 cur = coord + shift;
if ((0 <= cur.x) && (cur.x < width) && (0 <= cur.y) && (cur.y < height)) {
++num;
sum += read_image(input_image, cur);
}
}
}
write_image(output_image, coord, sum / num);
}