Hybrid screen design and automatic portrait image enhancement
Abstract
In this thesis, we present two research topics on printing and digital photography. The first topic is a hybrid screen design. The hybrid screen is a halftoning method that generates stochastic dispersed dot textures in highlights and periodic clustered dot textures in midtones. By applying an iterative halftoning algorithm such as direct binary search (DBS), each tone level is sequentially designed while satisfying the stacking constraint and guaranteeing a smooth transition between levels. In this thesis, we describe a complete design process for the hybrid screen, introduce a number of enhancements to the original hybrid screen, and evaluate their impact on print quality. These enhancements include a multilevel screen design based on either extending a bilevel screen or directly generating a multilevel screen on a high resolution grid, and extending the hybrid screen design procedure to color by jointly optimizing the color screens using color DBS. The second topic is an automatic portrait image enhancement by face beautification. We describe an automatic method for beautifying digital portraits by smoothing the skin of the face and enhancing the eyes. The method builds on existing face detection and face feature alignment technology to automatically segment the face and neck areas to be smoothed as well as the sclera and the iris boundaries. A smoothing filter is then selectively applied to the skin, while the color of the sclera is enhanced and the iris enlarged. The resulting portraits look like they have been professionally re-touched, but in a subtle and natural fashion.
Degree
Ph.D.
Advisors
Allebach, Purdue University.
Subject Area
Electrical engineering
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