Macro-uniformity refers to the subjective impression of overall uniformity in the print sample. By the efforts of INCITS
W1.1 team, macro-uniformity is categorized into five types of attributes: banding, streaks, mottle, gradients, and moiré
patterns, and the ruler samples are generated with perceptual scales. W1.1 macro-uniformity ruler is useful for judging
the levels of print defect, but it is not an easy task to reproduce the samples having the same perceptual scales at different
times in different places. An objective quantification method is more helpful and convenient for developers to analyze
print quality and design printing system components.
In this paper, we propose a method for measuring perceived macro-uniformity for a given print using a flat-bed scanner.
First, banding, 2D noise, and gradients are separately measured, and they are converted to the perceptual scales based on
subjective results of each attribute. The correlation coefficients between the measured values of the attributes and the
perceptual scales are 0.92, 0.97, and 0.86, respectively. Another subjective test is performed to find the relationship
between the overall macro-uniformity and the three attributes. The weighting factors are obtained by the experimental
result, and the final macro-uniformity grade is determined by the weighted sums of each attribute.
The techniques of one-dimensional projection in the spatial domain and contrast sensitivity function (CSF) are generally
used to measure banding. Due to the complex printing process of laser printers, hardcopy prints contain other 2D nonuniformities
such as graininess and mottle besides banding. The method of 1D projection is useful for extracting banding,
but it induces the confounding effect of graininess or mottle on the measurement of perceived banding. The appearance
of banding in laser printers is more similar to the sum of various rectangular signals having different amplitudes and
frequencies. However, in many cases banding is modeled as a simple sinusoidal signal and the CSF is frequently applied.
In this paper, we propose new measurement method of banding well correlated with human perception. Two kinds of
spatial features give a good performance to banding measurement. First the correlation factor between two adjacent 1D
signals is considered to obtain banding power which reduces the confounding effect of graininess and mottle. Secondly,
a spatial smoothing filter is designed and applied to reduce the less perceptible low frequency components instead of
using the CSF. By using moving window and subtracting the local mean values, the imperceptible low frequency
components are removed while the perceptible low frequency components like the sharp edge of rectangular waves are
preserved. To validate the proposed method, psychophysical tests are performed. The results show that the correlations
between the proposed method and the perceived scales are 0.96, 0.90, and 0.95 for black, cyan, and magenta,
We aim to quantify the perception of color gradation smoothness using objectively measurable properties. We propose a model to compute the smoothness of hardcopy color-to-color gradations. It is a gradient-based method that can be determined as a function of the 95th percentile of second derivative for the tone-jump estimator and the fifth percentile of first derivative for the tone-clipping estimator. Performance of the model and a previously suggested method were psychophysically appreciated, and their prediction accuracies were compared to each other. Our model showed a stronger Pearson correlation to the corresponding visual data, and the magnitude of the Pearson correlation reached up to 0.87. Its statistical significance was verified through analysis of variance. Color variations of the representative memory colors-blue sky, green grass and Caucasian skin-were rendered as gradational scales and utilized as the test stimuli.
Graininess and mottle described by ISO 13660 standard are two image quality attributes which are widely used to
evaluate area uniformity in digital prints. In an engineering aspect, it is convenient to classify and analyze high frequency
noise and low frequency noise separately. However, it is continuously reported in previous literature that the ISO
methods do not properly correlate with our perception. Since area quality is evaluated by observing all the characteristics
with a wide range of spectral frequencies in a printed page, it is almost impossible to differentiate between graininess and
mottle separately in our percept.
In this paper, we characterize '2D noise' print defect based on psychophysical experiments which appear as two
dimensional aperiodic fluctuations in digital prints. For each channel of cyan, magenta, and black, our approach is to use
two steps of hybrid filtering to remove invisible image components in the printed area. '2D noise' is computed as the
weighted sum of the graininess and mottle, which two weighting factors are determined by subjective evaluation
experiment. By conducting psychophysical validation experiments, the strong correlation is obtained between the
proposed metric and the perceived scales. The correlation coefficients r2 are 0.90, 0.86, and 0.78 for cyan, magenta and
Printer resolution is an important attribute for determining print quality, and it has been frequently referred to hardware optical resolution. However, the spatial addressability of hardcopy is not directly related to optical resolution because it is affected by printing mechanism, media, or software data processing such as resolution enhancement techniques (RET). The international organization ISO/IEC SC28 addresses this issue, and makes efforts to develop a new metric to measure this effective resolution. As the development process, this paper proposes a candidate metric for measuring printer resolution. Slanted edge method has been used to evaluate image sharpness for scanners and digital still cameras. In this paper, it is applied to monochrome laser printers. A test chart is modified to reduce the effect of halftone patterns. Using
a flatbed scanner, the spatial frequency response (SFR) is measured and modeled with a spline function. The frequency corresponding to 0.1 SFR is used in the metric for printer resolution. The stability of the metric is investigated in five separate experiments: (1) page to page variations, (2) different ROI locations, (3) different ROI sizes, (4) variations of toner density, and (5) correlation with visual quality. The 0.1 SFR frequencies of ten printers are analyzed. Experimental results show the strong correlation between a proposed metric and perceptual quality.
The same image on the display and color printer isn't the same. Firstly, this is due to the bit depth difference for
representing the color of a pixel. The display uses the color data of the eight or more bits, but the color printer uses just
1bit for representing color of a pixel. So, the display can reproduce smoother image than the color printer. Secondly, the
display gamut is larger than the printer gamut, so the display color is brighter and more saturate than the printer color.
For minimizing the problems due to these differences, many halftoning and gamut mapping techniques have been
developed. For the gamut mapping, color management standard organization, ICC, recommended 2 gamut mapping
methods, HPMINDE and SGCK. But the recommended methods by ICC have some weak points; contouring
(HPMINDE), paled pure color reproduction (SGCK) and too reddish hair color reproduction (HPMINDE, SGCK). This
paper introduces a gamut mapping method that can reproduce smooth gradation, pure colors with high saturation and
natural hair color. The proposed method is developed for optimal reproduction of graphic image, and it also gives good
results for pictorial image.
Due to subtle misalignment of optical components in the fabrication process, images projected by an optical light
modulator have severe line artifact along the direction of the optical scan. In this paper, we propose a novel methodology
to calibrate the modulator and generate the compensate image for the misaligned optical modulator in order to eliminate
the line artifact. A camera system is employed to construct Luminance Transfer Function (LTF) that characterizes the
optical modulator array. Spatial uniformity is obtained by redefining the dynamic range and compensating the
characteristic curvature of the LTF for each optical modulator array element. Simulation results show significant
reduction in the visibility of line artifact.
When time, temperature or an external environment change, a laser electrophotographic printer produces quite different color tones from original ones. To achieve consistent color reproduction, many researchers have tried to characterize printer tone curves and developed methods to correct color tones. Color channel independent methods are most widely used, and there are two approaches in color channel independent method: (1) Instrument-based correction and (2) visual correction. Two approaches provide some trade-offs between cost and accuracy. In this paper we propose a methodology which combines the strengths of these two approaches. We describe how we design a calibration page and how we characterize lightness variation of a reference patch. We then present the procedure of our global tone correction method based on visual appearance match of end-users as well as the predetermined reference lightness model. We simulate tone distortion state by varying hardware parameters, and perform visual appearance match experiments to subjects. Our experimental results show that our method can significantly reduce color difference between the original print and the print at the distortion state. This suggests that we can reliably estimate the distortion parameter, and correct tones close to an original state.