Advances in Technology of KODAK NEXPRESS Digital Production Color Presses

The stochastic screen has traditionally been used to preserve images with fine features as well as to reduce printing Moiré of images that contain input periodic structures. However, the stochastic screen also has experienced more difficulty in maintaining color stability in long press runs. Kodak, using its multilevel printing architecture, has created a new stochastic screening technology, with long-run color stability comparable to that of traditional screens. The new screening process has a unique AM and FM structure consisting of variable dot size, dot shape, dot density, and dot positions. The structure simulates the receptive field structure of the human retina to achieve the desired image smoothness. Kodak’s high information capacity, multilevel printing technology in conjunction with nonlinear LED exposure, can further be expanded to production printing with even finer contone-screen printing. This paper will discuss the advances of these technologies. Introduction Digital color halftoning [1] is commonly used in color image printing to either create the illusion of continuous tone when few intensity levels per primary colorant are available, or to affect visibility and objectionability of noise artifacts relative to direct continuous-tone (“contone”) printing. Rational tangent (RT) screening [2] is a popular technique for binary halftoning extended to multilevel halftone printing by Tai [3]. We generalized Tai’s approach to supercells [4] composed of cells of arbitrary polygonal shapes to facilitate AM/FM halftone screening under Kodak’s 8-bit multilevel electrophotographic (EP) printing architecture [5, 6], which allowed us to compare halftone and contone-screen reproduction of digital images at 600 dpi. Halftone image quality is known to be linked to whether quantization noise is white, blue [7], or green [8, 9], depending on its Fourier magnitude spectrum, which is useful to visualize in 2D as recommended in [10], because it matters how radially isotropic the spectrum is. Figure 1 shows a Fourier magnitude spectrum of a noise image corresponding to classical error diffusion [11]. Figure 1. Fourier magnitude spectrum of radially anisotropic blue noise Blue-noise masks [12, 13] and green-noise masks [14, 15] allow efficient implementation and yield more radially isotropic magnitude spectra, thus reducing correlated artifacts in the toe and shadow areas. Under the supercell approach, the fundamental frequency of a halftone screen in lines per inch (lpi) can be computed by the formula