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Related Concept Videos

Aliasing01:18

Aliasing

Accurate signal sampling and reconstruction are crucial in various signal-processing applications. A time-domain signal's spectrum can be revealed using its Fourier transform. When this signal is sampled at a specific frequency, it results in multiple scaled replicas of the original spectrum in the frequency domain. The spacing of these replicas is determined by the sampling frequency.
If the sampling frequency is below the Nyquist rate, these replicas overlap, preventing the original signal...
Linear Approximation in Frequency Domain01:26

Linear Approximation in Frequency Domain

Linear systems are characterized by two main properties: superposition and homogeneity. Superposition allows the response to multiple inputs to be the sum of the responses to each individual input. Homogeneity ensures that scaling an input by a scalar results in the response being scaled by the same scalar.
In contrast, nonlinear systems do not inherently possess these properties. However, for small deviations around an operating point, a nonlinear system can often be approximated as linear.
Convergence of Fourier Series01:21

Convergence of Fourier Series

The Fourier series is a powerful mathematical tool for representing periodic signals as an infinite sum of complex exponentials. In practice, this infinite series is truncated to a finite number of terms, yielding a partial sum. This truncation makes the approximation of the signal feasible but introduces certain challenges, particularly near discontinuities, known as the Gibbs phenomenon.
The Gibbs phenomenon refers to the persistent oscillations and overshoots that occur near discontinuities...
Upsampling01:22

Upsampling

Managing signal sampling rates is essential in digital signal processing to maintain signal integrity. A decimated signal, characterized by a reduced frequency range due to its lower sampling rate, can be upsampled by inserting zeros between each sample. This upsampling process expands the original spectrum and introduces repeated spectral replicas at intervals dictated by the new Nyquist frequency. To refine this zero-inserted sequence, it is passed through a lowpass filter with a cutoff...
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
Downsampling01:20

Downsampling

When considering a sampled sequence with zero values between sampling instants, one can replace it by taking every N-th value of the sequence. At these integer multiples of N, the original and sampled sequences coincide. This process, known as decimation, involves extracting every N-th sample from a sequence, thereby creating a more efficient sequence.
The Fourier transform of the decimated sequence reveals a combination of scaled and shifted versions of the original spectrum. This...

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Applying Hyperspectral Reflectance Imaging to Investigate the Palettes and the Techniques of Painters
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Applying Hyperspectral Reflectance Imaging to Investigate the Palettes and the Techniques of Painters

Published on: June 18, 2021

Analyzing halftone dot blurring by extended spectral prediction models.

Mathieu Hébert1, Roger David Hersch

  • 1Ecole Polytechnique Fédérale de Lausanne (EPFL), School of Computer and Communication Sciences, 1015 Lausanne, Switzerland. mathieu.hebert@univ-st-etienne.fr

Journal of the Optical Society of America. A, Optics, Image Science, and Vision
|December 26, 2009
PubMed
Summary

Classical spectral prediction models for bilevel halftones struggle with real-world continuous-level prints. This study extends these models, showing dot blurring increases effective ink coverage and can be modeled by adjusting the Yule-Nielsen model

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Area of Science:

  • Color Science
  • Print Technology
  • Optical Engineering

Background:

  • Spectral prediction models for halftone prints typically assume ideal, uniformly thick ink dots (bilevel halftones).
  • Real-world printing processes often result in continuous-level halftones where ink thickness varies at dot edges.
  • This variation deviates from the assumptions of classical models, potentially impacting prediction accuracy.

Purpose of the Study:

  • To evaluate the accuracy of classical Clapper-Yule and Yule-Nielsen models for continuous-level halftone prints.
  • To develop and validate extended spectral prediction models that account for variable ink thickness.
  • To quantify the impact of dot blurring on spectral reflectance prediction.

Main Methods:

  • Modeled continuous-level halftones by applying Gaussian filtering to bilevel halftone images to simulate variable thickness profiles.
  • Developed variable thickness extensions of the Clapper-Yule and Yule-Nielsen spectral prediction models.
  • Determined effective ink surface coverage by fitting the extended models to predicted reflectance spectra, analyzing the impact of dot blurring.

Main Results:

  • Dot blurring in continuous-level halftones increases effective ink surface coverage compared to the nominal coverage.
  • This increased coverage is a direct consequence of enhanced light absorption due to dot edge variations.
  • The Yule-Nielsen model can accurately predict reflectance spectra of continuous-level halftones when an adjusted 'n' value is used to account for dot blurring.

Conclusions:

  • Classical spectral prediction models require modification to accurately represent continuous-level halftones.
  • Dot blurring significantly influences spectral reflectance and must be incorporated into predictive models.
  • The extended Yule-Nielsen model, incorporating an adjusted 'n' value, offers a viable solution for predicting reflectance in real-world halftone prints.