single therad:

For row := 0 to image_row do
	For col := 0 to image_column do
		result_pixel := ∑ selected_pixel / pixel_count
	end
end


multi thread:

row_start := row_count / thread_count * nth -1
row_stop := row_count / thread_count * nth

For row := row_start to row_stop do
	For col := 0 to image_column do
		result_pixel := ∑ selected_pixel / pixel_count
	end
end