William C. Kress

ISO 19751 macro-uniformity

The ISO WD 19751 macro-uniformity team works towards the development of a standard for evaluation of perceptual image quality of color printers. The team specifically addresses the types of defects that fall in the category of macrouniformity, such as streaks, bands and mottle. The first phase of the standard will establish a visual quality ruler for macro-uniformity, using images with simulated macro-uniformity defects. A set of distinct, parameterized defects has been defined, as well as a method of combining the defects into a single image. The quality ruler will be a set of prints with increasing magnitude of the defect pattern. The paper will discuss the creation and printing of the simulated images, as well as initial tests of subjective evaluations using the ruler.

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.

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.

Scanners for Analytic Print Measurement - the devil in the details

Inexpensive and easy-to-use linear and area-array scanners have frequently substituted as colorimeters and densitometers for low-frequency (i.e., large area) hard copy image measurement. Increasingly, scanners are also being used for high spatial frequency, image microstructure measurements, which were previously reserved for high performance microdensitometers. In this paper we address characteristics of flatbed reflection scanners in the evaluation of print uniformity, geometric distortion, geometric repeatability and the influence of scanner MTF and noise on analytic measurements. Suggestions are made for the specification and evaluation of scanners to be used in print image quality standards that are being developed.

Characterization of reflection scanner uniformity

A flatbed reflection scanner is a tempting device to use as a surrogate for a microdensitometer in the evaluation of print image quality. Since reflection scanners were never designed with this purpose in mind, many concerns exist regarding their usefulness as a microdensitometer surrogate. This paper addresses the concerns regarding scan uniformity that must be addressed in order to qualify a reflection scanner for use in print image quality evaluation.

W1.1 macro-uniformity

The INCITS W1.1 macro-uniformity team works towards the development of a standard for evaluation of perceptual image quality of color printers. The team specifically addresses the types of defects that fall in the category of macrouniformity, such as streaks, bands and mottle. This paper provides a brief summary of the status of this work, and describes recent results regarding the precision of the macro-uniformity quality ruler for assessment of typical printer defects.

INCITS W1.1 macro-uniformity

This paper describes the status of the INCITS W1.1 macro-uniformity ad hoc team, towards development of standards for perceptual image quality for color printers. The team has defined the macro-uniformity attribute, has developed several test patterns to be used for subjective and objective evaluations and has defined test patterns and methods to address color conversions of digitizing devices. A set of print samples, originating from diverse printing systems, has been established, and digitization of these samples is in progress. These activities and next steps are reviewed in this paper.

Update on INCITS W1.1 standard for perceptual evaluation of micro-uniformity

INCITS W1 is the U.S. representative of ISO/IEC JTC1/SC28, the standardization committee for office equipment. In September 2000, INCITS W1 was chartered to develop an appearance-based image quality standard. The resulting W1.1 project is based on a proposal that perceived image quality could be described by a small set of broad-based attributes. There are currently five ad hoc W1.1 teams, each working on one or more of these image quality attributes. This paper summarizes the work of the W1.1 Microuniformity ad hoc team. The agreed-upon process for developing the W1.1 Image Quality of Printers standards is described in a statement located on the INCITS W1.1 web site (ncits.org/tc_home/w11htm/incits_w11.htm), and the process schematic is reproduced here as Figure 1, (in which a final, independent confirmation step has been excluded for brevity).

Digitization and metric conversion for image quality test targets: Part II

A common need of the INCITS W1.1 Macro Uniformity, Color Rendition and Micro Uniformity ad hoc efforts is to digitize image quality test targets and derive parameters that correlate with image quality assessments. The digitized data should be in a colorimetric color space such as CIELAB and the process of digitizing will introduce no spatial artifacts that reduce the accuracy of image quality parameters. Input digitizers come in many forms including inexpensive scanners used in the home, a range of sophisticated scanners used for graphic arts and scanners used for scientific and industrial measurements (e.g., microdensitometers). Some of these are capable of digitizing hard copy output for image quality objective metrices, and this report focuses on assessment of high quality flatbed scanners for that role. Digitization using flatbed scanners is attractive because they are relatively inexpensive, easy to use, and most are available with document feeders permitting analysis of a stack of documents with little user interaction. Other authors have addressed using scanners for image quality measurements. This paper focuses (1) on color transformations from RGB to CIELAB and (2) sampling issues and demonstrates that flatbed scanners can have a high level of accuracy for generating accurate, stable images in the CIELAB metric. Previous discussion and experimental results focusing on color conversions had been presented at PICS 2003. This paper reviews the past discussion with some refinement based on recent experiments and extends the analysis into color accuracy verification and sampling issues.