Dmitri Anatolyevich Gusev

Update on the INCITS W1.1 standard for evaluating the color rendition of printing systems

The color rendition ad hoc team of INCITS W1.1 is working to address issues related to color and tone reproduction for printed output and its perceptual impact on color image quality. The scope of the work includes accuracy of specified colors with emphasis on memory colors, color gamut, and the effective use of tone levels, including issues related to contouring. The team has identified three sub-attributes of color rendition: (1) color quantization -- defined as the ability to merge colors where needed, (2) color scale -- defined as the ability to distinguish color where needed, and (3) color fidelity -- defined as the ability to match colors. Visual definitions and descriptions of how these sub-attributes are perceived have been developed. The team is presently defining measurement methods for these, with the first of the sub-attributes considered being color quantization. More recently, the problem of measuring color fidelity has been undertaken. This presentation will briefly review the definitions and appearance of the proposed sub-attributes. The remainder of the discussion will focus on the progress to date of developing test targets and associated measurement methods to quantify the color quantization and color fidelity sub-attributes.

Hybrid algorithms for digital halftoning and their application to medical imaging

Abstract Error diffusion, ordered dither, and patterning are well-known digital halftoning techniques, each with its advantages and disadvantages. Error diffusion is known for correlated artifacts looking like zebra stripes. Images produced by ordered dither and patterning suffer from artificial contours in slowly varying regions of pictures. Use of ordered matrices by both ordered dither and patterning results in poor rendition of small details, so the images appear blurred. We discuss how the modified Floyd-Steinberg error diffusion algorithm reduces correlated artifacts compared to the classical Floyd-Steinberg algorithm without increase in the amount of work. It also simplifies combining of error diffusion with other methods. We introduce two families of hybrid algorithms. One of them combines the modified Floyd-Steinberg algorithm with ordered dither and the other one combines it with patterning. We fight the correlated artifacts with ordered matrices while reducing the accompanying artificial contours by error diffusion. The latter achievement allows us to use smaller matrices and thus affect small detail representation at low resolutions. We show that hybrid algorithms are useful for digital simulation of classical screens. Combining error diffusion and patterning results in speedups essential for printing medical images at high resolutions. The article considers application of the hybrid algorithms to printing of medical images on laser printers.

Estimating from outputs of oversampled delta-sigma modulation

Oversampling a delta-sigma-modulated sequence, one can compute unbiased sample estimates of averages of consecutive input elements for a wide variety of inputs. We prove that these estimates are most efficient in their class (that is, variances of sample means are minimum in the class of random binary sequences gn n = 1,…, N, such that the expected values of gn are equal to the values of the corresponding inputs of delta-sigma modulation) and consistent. Delta-sigma modulation may also be described as one-dimensional error diffusion (a technique for digital halftoning). However, delta-sigma modulation is not a practical digital halftoning algorithm, because human vision averages small luminance deviations in two dimensions. We pose an open problem that invites the reader to extend our approach to the two-dimensional case for the purpose of development of a practical digital halftoning algorithm.

Recent Progress in the Development of INCITS W1.1, Appearance-Based Image Quality Standards for Printers

In September 2000, INCITS W1 (the U.S. representative of ISO/IEC JTC1/SC28, the standardization committee for office equipment) was chartered to develop an appearance-based image quality standard.(1),(2) The resulting W1.1 project is based on a proposal(4) that perceived image quality can be described by a small set of broad-based attributes. There are currently five ad hoc teams, each working towards the development of standards for evaluation of perceptual image quality of color printers for one or more of these image quality attributes. This paper summarizes the work in progress of the teams addressing the attributes of Macro-Uniformity, Color Rendition, Text and Line Quality and Micro-Uniformity.