Uniqueness of Bilevel Image Degradations

Two major degradations, edge displacement and corner erosion, change the appearance of bilevel images. The displacement of an edge determines stroke width, and the erosion ofa corner affects crispness. These degradations are functions of the system parameters: the point spread function (PSF) width and functional form, and the binarization threshold. Changing each of these parameters will affect an image differently. A given amount of edge displacement or amount of erosion of black or white corners can be caused by several combinations of the PSF width and the binarization threshold. Any pair of these degradations are unique to a single PSF width and binarization threshold for a given PSF function. Knowledge of all three degradation amounts provides information that will enable us to determine the PSF functional form from the bilevel image. The effect of each degradation on characters will be shown. Also, the uniqueness of the degradation triple {dw\u3e db, δc} and the effect of selecting an incorrect PSF functional form will be shown, first with relation to PSF width and binarization threshold estimate, then for how this is visible in sample characters

Scanner Parameter Estimation Using Bilevel Scans of Star Charts

Scanning a high contrast image in bilevel mode results in image degradation. This is caused by two primary effects: blurring and thresholding. This paper expands on a method of estimating a joint distortion parameter, called the edge spread, from a star sector test chart in order to calculate the values of the point spread function width and binarization threshold. This theory is also described for variations in the source pattern which can represent degradations caused by repetition of the bilevel process as would be seen in printing then scanning, or in repeated photocopying. Estimation results are shown for the basic and extended cases

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.(J),(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

Estimating Scanning Characteristics from Corners in Bilevel Images

Degradations that occur during scanning can cause errors in Optical Character Recognition (OCR). Scans made in bilevel mode (no grey scale) from high contrast source patterns are the input to the estimation processes. Two scanner system parameters are estimated from bilevel scans using models of the scanning process and bilevel source patterns. The scanner\u27s point spread function (PSF) width and the binarization threshold are estimated by using corner features in the scanned images. These estimation algorithms were tested in simulation and with scanned test patterns. The resulting estimates are close in value to what is expected based on grey-level analysis. The results of estimation are used to produce synthetically scanned characters that in most cases bear a strong resemblance to the characters scanned on the scanner at the same settings as the test pattern used for estimation

Relating Electrophotographic Printing Model and IS013660 Standard Attributes

A mathematical model of the electrophotographic printing process has been developed. This model can be used for analysis. From this a print simulation process has been developed to simulate the effects of the model components on toner particle placement. A wide variety of simulated prints are produced from the model\u27s three main inputs, laser spread, charge to toner proportionality factor and toner particle size. While the exact placement of toner particles is a random process, the total effect is not. The effect of each model parameter on the ISO 13660 print quality attributes line width, fill, raggedness and blurriness is described

An Analysis of Binarization Ground Truthing

The accuracy of a binarization algorithm is often calculated relative to a ground truth image. Except for synthetically generated images, no ground truth image exists. Evaluating binarization on real images is preferred. The ground truthing between and among different operators is compared. Four direct metrics were used. The variability of the results of five different automatic binarization algorithms were compared to that of manual ground truth results. Significant variability in the ground truth results was found

PSF Estimation by Gradient Descent Fit to the ESF

Calibration of scanners and cameras usually involves measuring the point spread function (PSF). When edge data is used to measure the PSF, the differentiation step amplifies the noise. A parametric fit of the functional form of the edge spread function (ESF) directly to the measured edge data is proposed to eliminate this. Experiments used to test this method show that the Cauchy functional form fits better than the Gaussian or other forms tried. The effect of using a functional form of the PSF that differs from the true PSF is explored by considering bilevel images formed by thresholding. The amount of mismatch seen can be related to the difference between the respective kurtosis factors

New Metric Describes Edge Noise in Bilevel Images

A new approach enables quantitative and qualitative characterization of varying edge noise even if the additive noise level is constant

Printer Modeling for Document Imaging

The microscopic details of printing often are unnoticed by humans, but can make differences that affect machine recognition of printed text. Models of the defects introduced into images by printing can be used to improve machine recognition. A probabilistic model used to generate images showing toner placement bears similarities to actual printed images. An equation derived for the average coverage of paper by toner particles having probabilistic placement is developed using geometric probability. Simulations show that averages of ‘printed images’ do have the same average coverage as the derived average coverage equations

Partitioning of the Degradation Space for OCR Training

Generally speaking optical character recognition algorithms tend to perform better when presented with homogeneous data. This paper studies a method that is designed to increase the homogeneity of training data, based on an understanding of the types of degradations that occur during the printing and scanning process, and how these degradations affect the homogeneity of the data. While it has been shown that dividing the degradation space by edge spread improves recognition accuracy over dividing the degradation space by threshold or point spread function width alone, the challenge is in deciding how many partitions and at what value of edge spread the divisions should be made. Clustering of different types of character features, fonts, sizes, resolutions and noise levels shows that edge spread is indeed shown to be a strong indicator of the homogeneity of character data clusters