No abstract
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 an 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 a balance of colorimetric accuracy, in cases where a reference exists, and pleasing overall color appearance. Visual definitions and descriptions of how these sub-attributes are perceived have been developed. The team is presently working to define measurement methods for the subattributes, with the focus in 2004 being on color fidelity. This presentation will briefly review the definitions and appearance of the proposed subattributes and the progress to date of developing test targets and associated measurement methods to quantify the color quantization sub-attribute. The remainder of the discussion will focus on the recent progress made in developing measurement methods for the color fidelity sub-attribute.
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 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.
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 an 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 a balance of colorimetric accuracy, in cases where a reference exists, and pleasing overall color appearance. Visual definitions and descriptions of how these sub-attributes are perceived have been developed. The team is presently working to define measurement methods for the subattributes, with the focus in 2004 being on color fidelity. This presentation will briefly review the definitions and appearance of the proposed subattributes and the progress to date of developing test targets and associated measurement methods to quantify the color quantization sub-attribute. The remainder of the discussion will focus on the recent progress made in developing measurement methods for the color fidelity sub-attribute.
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.
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