<title>Digitization and metric conversion for image quality test targets: Part II</title>

Abstract

A common need of the INCITS Wi.i'' 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 metrics, 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 measurements3'4. 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 2OO3. This paper reviews the past discussion with some refinement based on recent experiments and extends the analysis into color accuracy verification and sampling issues.

Scanners for analytic print measurement: the devil in the details

“…This can be done by transforming tolerances into scanner signal values or transforming scanner signals into colorimetric coordinates. 5 Typical scannerinduced bias and variation should be kept to some fraction of the test tolerance.…”