High-speed first- and second-order frequency modulated halftoning

Abstract

Abstract. Halftoning is a crucial part of image reproduction in print. First-order frequency modulated (FM) halftones, in which the single dots are stochastically distributed, are widely used in printing technologies, such as inkjet, that are able to stably print isolated dispersed dots. Printers, such as laser printers, that utilize electrophotographic technology are not able to stably print the isolated dots and, therefore, use clustered-dot halftones. Periodic clustered-dot, i.e., amplitude modulated halftones are commonly used in this type of printer, but they suffer from an undesired periodic interference pattern called moiré. An alternative solution is to use second-order FM halftones in which the clustered dots are stochastically distributed. The iterative halftoning techniques that usually result in well-formed halftones operate on the whole input image and require extensive computations and thus, are very slow when the input image is large. We introduce a method to generate image-independent threshold matrices for first-and second-order FM halftoning. The first-order threshold matrix generates well-formed halftone patterns and the second-order FM threshold matrix can be adjusted to produce clustered dots of different sizes, shapes, and alignment. Using predetermined and image-independent threshold matrices makes the proposed halftoning method a point-by-point process and thereby very fast. 1 Introduction Many reproduction devices, e.g., printers, have a limited number of output states, leaving the choice of printed and nonprinted spots in order to reproduce a shade. Thus, continuous tone gray-scale or color images need to go through a process called halftoning before being printed. Because of the fact that the human eye is limited in its capacity to resolve small dots and dots close to each other, if the viewing distance is long or the dots are small enough, the human eye is not able to distinguish between the original image and the halftone one. Hence, since the human eye acts as a lowpass filter, the halftones appear pleasing if the difference between the original and the halftone is small in the low-frequency region.Halftoning algorithms are commonly categorized into two main subgroups, called amplitude modulated (AM) and frequency modulated (FM). In AM, i.e., periodic clustered-dot halftones, different shades of gray are reproduced by changing the size of the dots while keeping their spacing constant. In first-order FM, dispersed-dot halftones, on the other hand, the size of the dots is constant while their density (or frequency) is variable. There is also another type of halftones, which we call second-order FM in this paper, in which both the size and the frequency are variables. In these halftones, the clustered dots are stochastically distributed. In literature, this type of halftones is also referred to as stochastic clustered-dot halftones and even green-noise dither patterns. In Ref. 1, the radially averaged power spectrum (RAPS) curves for these three types of halftones, i.e., AM, firstorder...

3D Surface Structures and 3D Halftoning

“…Other halftone structures are also possible to generate by using other filters than the Gaussian filter in Eq. 1 [9]. Another important aspect of IMCDP is that, it can also generate second-generation FM, i.e.…”

“…In this type of FM methods, the single dots are distributed "stochastically". There is also another type of FM method, referred to as the 2 nd generation FM halftoning in this paper, that "stochastically" distribute the clustered dots [9]. One of the advantages of the 2 nd generation FM halftoning over the 1 st generation FM is that the former one results in halftones that give less grainy impression in the areas of an image where the tones vary smoothly.…”

Improving image quality in multi-channel printing - multilevel halftoning, color separation and graininess characterization

“…Secondly, as any iterative halftoning algorithm, processing time is increased in comparison to algorithms that operate point-bypoint or on a neighborhood. This issue has been addressed in Gooran and Kruse (2015), in which a high speed version of the IMCDP algorithm has been developed. It is based on the original algorithm, creating image-independent first or second generation FM threshold matrices, thus achieving a fast binarization.…”

“…This makes the algorithm more computationally challenging, although the result is a high quality halftoned image (Kacker and Allebach, 1998, Gooran, 2001, Bernal et al, 2014, Gooran and Kruse, 2015.…”

“…For additional details, the interested readers are referred to the original article (Gooran and Kruse, 2015 …”