A Simple Approach in Digitising a Photographic Collection

This paper reviews the processes involved in the digitisation, display and storage of medium size collections of photographs using simple and inexpensive, commercially available equipment. It is also aimed to provide a guideline for evaluating the performance of such imaging devices on aspects of image quality. A collection of slides, representing first-generation analogue reproductions of a photographic collection from the nineteenth century, is treated as a case study. Constraints on the final image quality and the implications on the digital archive are discussed along with a presentation of device characterisation and calibration procedures. Summary results from objective measurements carried out to assess the systems are presented. The issues of file-format, physical storage and data migration are also addressed

Measurements of the modulation transfer function of image displays

Measurements of the Modulation Transfer Function (MTF) of image displays are often required for objective image quality assessments, but are difficult to carry out due to the need for specialized apparatus. This article presents a simple method for the measurement of the MTF of a sample CRT display system which involves the use of a still digital camera for the acquisition of displayed test targets. Measurements are carried out using, first, the sine wave method, where a number of artificial sine wave images of discrete spatial frequency and constant modulation are captured from a close distance. Fourier techniques are employed to extract the amplitude of the display signal from the resulting macroimages. In a second phase, displayed artificial step edges are captured, and the ISO 12333 SFR (Spatial Frequency Response) Slanted Edge plug-in is used for automatic edge analysis. The display MTF, in both cases, is cascaded from the closed-loop system MTF. The two measuring techniques produced matching results, indicating that under controlled test conditions accurate measurements of the display MTF can be achieved with the use of relatively simple equipment

Noise Power Spectrum Scene-Dependency in Simulated Image Capture Systems

The Noise Power Spectrum (NPS) is a standard measure for image capture system noise. It is derived traditionally from captured uniform luminance patches that are unrepresentative of pictorial scene signals. Many contemporary capture systems apply non- linear content-aware signal processing, which renders their noise scene-dependent. For scene-dependent systems, measuring the NPS with respect to uniform patch signals fails to characterize with accuracy: i) system noise concerning a given input scene, ii) the average system noise power in real-world applications. The scene- and-process-dependent NPS (SPD-NPS) framework addresses these limitations by measuring temporally varying system noise with respect to any given input signal. In this paper, we examine the scene-dependency of simulated camera pipelines in-depth by deriving SPD-NPSs from fifty test scenes. The pipelines apply either linear or non-linear denoising and sharpening, tuned to optimize output image quality at various opacity levels and exposures. Further, we present the integrated area under the mean of SPD-NPS curves over a representative scene set as an objective system noise metric, and their relative standard deviation area (RSDA) as a metric for system noise scene-dependency. We close by discussing how these metrics can also be computed using scene-and-process- dependent Modulation Transfer Functions (SPD-MTF)

A case study in digitizing a photographic collection

This paper reviews the processes involved in the digitisation, display and storage of medium size collections of photographs using mid-range commercially available equipment. Guidelines for evaluating the performance of these digitisation processes based on aspects of image quality are provided. A collection of photographic slides, representing first-generation analogue reproductions of a photographic collection from the nineteenth century, is treated as a case study. Constraints on the final image quality and the implications of digital archiving are discussed. Full descriptions of device characterisation and calibration procedures are given and results from objective measurements carried out to assess the digitisation system are presented. The important issues of file format, physical storage and data migration are also addressed

Scene classification with respect to image quality measurements

Psychophysical image quality assessments have shown that subjective quality depended upon the pictorial content of the test images. This study is concerned with the nature of scene dependency, which causes problems in modeling and predicting image quality. This paper focuses on scene classification to resolve this issue and used K-means clustering to classify test scenes. The aim was to classify thirty two original test scenes that were previously used in a psychophysical investigation conducted by the authors, according to their susceptibility to sharpness and noisiness. The objective scene classification involved: 1) investigation of various scene descriptors, derived to describe properties that influence image quality, and 2) investigation of the degree of correlation between scene descriptors and scene susceptibility parameters. Scene descriptors that correlated with scene susceptibility in sharpness and in noisiness are assumed to be useful in the objective scene classification. The work successfully derived three groups of scenes. The findings indicate that there is a potential for tackling the problem of sharpness and noisiness scene susceptibility when modeling image quality. In addition, more extensive investigations of scene descriptors would be required at global and local image levels in order to achieve sufficient accuracy of objective scene classification

Perceptual image attribute scales derived from overall image quality assessments

Psychophysical scaling is commonly based on the assumption that the overall quality of images is based on the assessment of individual attributes which the observer is able to recognise and separate, i.e. sharpness, contrast, etc. However, the assessment of individual attributes is a subject of debate, since they are unlikely to be independent from each other. This paper presents an experiment that was carried to derive individual perceptual attribute interval scales from overall image quality assessments, therefore examine the weight of each individual attribute to the overall perceived quality. A psychophysical experiment was taken by fourteen observers. Thirty two original images were manipulated by adjusting three physical parameters that altered image blur, noise and contrast. The data were then arranged by permutation, where ratings for each individual attribute were averaged to examine the variation of ratings in other attributes. The results confirmed that one JND of added noise and one JND of added blurring reduced image quality more than did one JND in contrast change. Furthermore, they indicated that the range of distortion that was introduced by blurring covered the entire image quality scale but the ranges of added noise and contrast adjustments were too small for investigating the consequences in the full range of image quality. There were several interesting tradeoffs between noise,blur and changes in contrast. Further work on the effect of (test) scene content was carried out to objectively reveal which types of scenes were significantly affected by changes in each attribute

Preferred Tone Reproduction of Images on Soft Displays

A series of psychophysical experiments have been carried out to investigate the preferred subjective contrast of displayed images. The contrast of the displayed images was evaluated with the use of a gamma model which involved cascading the gamma values of the individual components of the imaging system. The preferred contrast was found to be scene dependent and varied between 1.56 and 1.96 when images where viewed in total darkness. Probit analysis on the distributions of preferred gamma values showed that the probits of those scenes which had extremes in contrast were outside the confidence limits of other more representative scenes. The validity and implications of applying the gamma model to determine the tone reproduction of an imaging system has been investigated

An evaluation of MTF determination methods for 35mm scanners

Three different techniques were used to determine the Modulation Transfer Function (MTF) of a 35mm film scanner. The first involved scanning sine wave charts comprising a number of patches with different frequencies of known modulation. The second method involved the scanning and Fourier transform of a photographic grain noise pattern to simulate low modulation white noise. Finally, the ISO 12233 Slanted-edge Spatial Frequency Response (SFR) plug-in was used to determine the average MTF of the device. This creates a super-sampled edge profile from sequential scan-lines of the sampled image of an edge. Procedures for creating test targets, where appropriate, are described. Advantages and limitations encountered in applying each methodology are discussed, as well as the precision of each method for deriving the MTF. Conclusions are drawn concerning the comparability of MTFs determined by the three methods

Demographic factors influencing consent for cadaver organ donation

The records of all donor referrals to Groote Schuur Hospital over a 5½-year period were retrospectively examined to determine which factors influenced the families' decision on organ donation. In 35% of these referrals the families were not approached for consent. The reasons for this included the potential donor being unsuitable for organ donation or not meeting all the criteria for brain death. The effects of the age, sex, race and the cause of death of the potential donor on whether the family gave consent were investigated. This study demonstrates that consent was given more readily when the potential donor was aged ≥10 years, that the sex of the potential donor appeared to have no effect on the decision by the family about organ donation, that black families gave consent for organ donation less frequently than families of other race groups and that consent was obtained more easily when death was due to suicide

Scene-and-Process-Dependent Spatial Image Quality Metrics

Spatial image quality metrics designed for camera systems generally employ the Modulation Transfer Function (MTF), the Noise Power Spectrum (NPS), and a visual contrast detection model. Prior art indicates that scene-dependent characteristics of non-linear, content-aware image processing are unaccounted for by MTFs and NPSs measured using traditional methods. We present two novel metrics: the log Noise Equivalent Quanta (log NEQ) and Visual log NEQ. They both employ scene-and-process-dependent MTF (SPD-MTF) and NPS (SPD-NPS) measures, which account for signal-transfer and noise scene-dependency, respectively. We also investigate implementing contrast detection and discrimination models that account for scene-dependent visual masking. Further, three leading camera metrics are revised that use the above scene-dependent measures. All metrics are validated by examining correlations with the perceived quality of images produced by simulated camera pipelines. Metric accuracy improved consistently when the SPD-MTFs and SPD-NPSs were implemented. The novel metrics outperformed existing metrics of the same genre