The electronic holography using reflection-type multiple spatial light modulators have limited scalability in size of reconstructed three-dimensional image. We propose a newly devised space-saving image-readout optical system to overcome the upper limit of image size scalability in former method. We apply it with 16 (4$\times$4) 4K$\times$2K-pixel SLMs to display larger full-parallax color holographic three-dimensional (3D) video than with the previous system.