I wonder if in fact that 120 figure actually does refer to a pixels per cm. parameter (ppc or dpc). The OP says it is "for printing" and if so that resolution, 120 dpi and 720 x1000 pixels, is strangely low for a print. However, the standard prescription for printing, 300 ppi, would have a metric equivalent of 120 ppc. I think it likely that the desired resolution is 1,800 x 2,520 pixels.
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