Large Image Processing / composing

HI, im running a virtual server and like to process / compose large images (~20.000 x 20.000 px). PHP, GD & Imagemagick are installed. Processing of images must work in parts so that it works on my server. To do (Image names & canvas size are in variables): // 1) set canvas size canvas-size-h = 18898; // pixels canvas-size-v = 23622; // pixels // 2) fill canvas with background color background-color = #787878; --> see [login to view URL] // 3) add Layer above background and fill canvas as repeating pattern (image) image = [login to view URL]; --> see 2-canvas-with filled [login to view URL] // 4) fill canvas with alpha channel image as repeating pattern -> see [login to view URL] alpha = [login to view URL]; // 5) apply alpha channel (filled) on 3) image --> see 4-result-with [login to view URL] -> create image and save on server