60 Colour Image Segmentation Technique for Screen Printing Proceedings of the Technical Sessions, 27 (2011) 60-67 Institute of Physics – Sri Lanka Colour Image Segmentation Technique for Screen Printing R.U. Hewage and D.U.J. Sonnadara Department of Physics, University of Colombo, Sri Lanka ABSTRACT Screen-printing is an industry with a large number of applications ranging from printing mobile phone logos to printing artworks on fabrics. In screen-printing, image segmentation plays a critical role in deciding both the cost and the quality attributes of printing. The work presented in this paper focuses on the development of an approach to colour image segmentation using a combined approach of k-means clustering and principal component analysis. The uncorrelated image data obtained through a principal component analysis was clustered using a k-means clustering algorithm. Since the study focused on the screen printing industry, the selection of the number of clusters k which is the most critical element is allowed to be set manually so that users can limit the number of colours to be segmented. It is shown that this approach produces a significant improvement in colour image segmentation. Results are also compared with another popular clustering algorithm called the mean-shift, which is normally used in feature space clustering. 1. INTRODUCTION The introduction to screen printing given in Wikipedia is as follows [1]. “Screen printing is a printing technique that uses a woven mesh to support an ink blocking stencil. The attached stencil forms open areas of mesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate. A roller or squeegee is moved across the screen stencil, forcing or pumping ink past the threads of the woven mesh in the open areas. Screen printing is also a stencil method of print making in which a design is imposed on a screen of silk or other fine mesh, with blank areas coated with an impermeable substance, and ink is forced through the mesh onto the printing surface”. From the very beginning, screen-printing is associated with fabrics. Today even modern mobile phone’s logos are printed using screen printing methodologies. The image segmentation plays a crucial role in screen-printing. Currently in the local industry, where this research was focused, the colour separation is done manually. Trained graphic artists manually draw the artwork to get separate layers of different colours. Some use software packages such as Adobe Illustrator and Adobe Photoshop to help this work. Some use sample manual drawings constructed by the graphic artists on an artwork to segment the artwork according to its respective colours. Each of the segmented films contains different colour segments of the original artwork. However, manual methods are time consuming and require skilled human resources. The research work discussed in this paper focused on producing segmented images from original artwork with very little manual effort.