Coating a printed surface with a smooth transparent layer can modify its color. This is due to light interreflections within the coating layer which produce a halo-shaped point spread function. The change of color is related to the coating thickness and the halftone screening used for printing. Thanks to an optical model able to predict the spectral reflectance of the coated print from the one of the non-coated print, we propose to study the impact of the halftone pattern (shape and profile) on the color change caused by the coating layer. It was found that line halftone patterns with a crenel profile induces the strongest changes of color. This is therefore the pattern that we use for an innovative application of this phenomenon: revealing a binary image by adding or removing a coating layer on the print that is originally uniform.
An alignment approach for data-bearing halftone images, which are a visually pleasant alternative to barcodes, is proposed in this paper. In this paper, we address the alignment problem of data-bearing halftone images on a 3D surface. Different types of surfaces have been tested , using our proposed approach, and high accuracy results have been achieved. Additionally, we also develop a data retrieval tool from an aligned image, in order to decode the data embedded in the original image. A system to assess the accuracy of alignment is introduced to quantify the effectiveness of the proposed alignment approach.