User Preference in Detail-Enhancement Adjustments for Images Captured by Camera Phones

Most smartphones now come with an integrated camera. Such a smartphone is called a camera phone. Popularity of camera phones is rising and it is expected that 87.8% of United States population will possess camera phones by year 2020 (Euromonitor International, 2017). A camera phone’s workflow for capturing, editing, and sharing images on social media has become very efficient. Its ease of use, accessibility, and automatic exposure settings to capture an image has contributed to its popularity. Camera phones are more compact and convenient than professional DSLR cameras. The popularity of this technology has created a need to study and evaluate image quality of photographs from the camera phone. Numerous image-editing applications and adjustments are available to edit these images on the phone itself. Previous studies have shown the reasons why people like to edit their images captured by camera phones (Bakhshi et al., 2014; Bakhshi et al., 2015). This psychophysical study aims to determine the preference related to detail-enhancement adjustments for images captured by camera phones. The image contents used in this study are selfies and food images. Images possessing two levels of high and low ISO were evaluated. The stimuli for the psychophysical experiment were created by editing these images with clarity, contrast and sharpness adjustments. By recording participants’ response and analyzing the data, observers’ preference were determined for different detail-enhancement (DE) adjustments and content of images captured by camera phones. Results showed that the preference for detail-enhancement adjustments was subjective and varied by both person and image. Participants preferred low ISO DE images more than high ISO DE images. Overall, only slight preferences were observed between images possessing different DE adjustments, DE levels and contents, but a significant preference was not observed in any of these variables

Spectral imaging of human portraits and image quality

This dissertation addresses the problem of capturing spectral images for human portraits and evaluating image quality of spectral images. A new spectral imaging approach is proposed in this dissertation for spectral images of human portraits. Thorough statistical analysis is performed for spectral reflectances from various races and different face parts. A spectral imaging system has been designed and calibrated for human portraits. The calibrated imaging system has the ability to represent not only the facial skin but also the spectra of lips, eyes and hair from various races as well. The generated spectral images can be applied to color-imaging system design and analysis. To evaluate the image quality of spectral imaging systems, a visual psychophysical image quality experiment has been performed in this dissertation. The spectral images were simulated based on real spectral imaging system. Meaningful image quality results have been obtained for spectral images generated from different spectral imaging systems. To bridge the gap between the physical measures and subjective visual perceptions of image quality, four image distortion factors were defined. Image quality metrics were obtained and evaluated based statistical analysis and multiple analysis. The image quality metrics have high correlation with subjective assessment for image quality. The image quality contribution of the distortion factors were evaluated. As an extension of the work other researchers in MCSL have initiated, this dissertation research will, working with other researchers in MCSL, put effort to build a publicly accessible database of spectral images, Lippmann2000

A Log NEQ based comparison of several silver halide and electronic pictorial imaging systems

A protocol for determining log NEQ and a new metric, the Equivalent Image Quality or EIQ, are presented for the generalized experimental evaluation of noise related monochrome pictorial image quality. These metrics are then applied to the evaluation of a pictorial CCD camera and several pictorial films. Emphasis is placed on the development and verification of experimental techniques which do not require elaborate equipment or support facilities. Data analysis is conducted using only available software packages and personal computers. Conclusions are drawn concerning the performance of CCD based and silver halide imaging systems which allow for the objective comparison of the images they produce, and the fundamental differences in the characteristics and requirements of the two systems as applied to pictorial imaging are noted

Kuvanlaatukokemuksen arvionnin instrumentit

This dissertation describes the instruments available for image quality evaluation, develops new methods for subjective image quality evaluation and provides image and video databases for the assessment and development of image quality assessment (IQA) algorithms. The contributions of the thesis are based on six original publications. The first publication introduced the VQone toolbox for subjective image quality evaluation. It created a platform for free-form experimentation with standardized image quality methods and was the foundation for later studies. The second publication focused on the dilemma of reference in subjective experiments by proposing a new method for image quality evaluation: the absolute category rating with dynamic reference (ACR-DR). The third publication presented a database (CID2013) in which 480 images were evaluated by 188 observers using the ACR-DR method proposed in the prior publication. Providing databases of image files along with their quality ratings is essential in the field of IQA algorithm development. The fourth publication introduced a video database (CVD2014) based on having 210 observers rate 234 video clips. The temporal aspect of the stimuli creates peculiar artifacts and degradations, as well as challenges to experimental design and video quality assessment (VQA) algorithms. When the CID2013 and CVD2014 databases were published, most state-of-the-art I/VQAs had been trained on and tested against databases created by degrading an original image or video with a single distortion at a time. The novel aspect of CID2013 and CVD2014 was that they consisted of multiple concurrent distortions. To facilitate communication and understanding among professionals in various fields of image quality as well as among non-professionals, an attribute lexicon of image quality, the image quality wheel, was presented in the fifth publication of this thesis. Reference wheels and terminology lexicons have a long tradition in sensory evaluation contexts, such as taste experience studies, where they are used to facilitate communication among interested stakeholders; however, such an approach has not been common in visual experience domains, especially in studies on image quality. The sixth publication examined how the free descriptions given by the observers influenced the ratings of the images. Understanding how various elements, such as perceived sharpness and naturalness, affect subjective image quality can help to understand the decision-making processes behind image quality evaluation. Knowing the impact of each preferential attribute can then be used for I/VQA algorithm development; certain I/VQA algorithms already incorporate low-level human visual system (HVS) models in their algorithms.Väitöskirja tarkastelee ja kehittää uusia kuvanlaadun arvioinnin menetelmiä, sekä tarjoaa kuva- ja videotietokantoja kuvanlaadun arviointialgoritmien (IQA) testaamiseen ja kehittämiseen. Se, mikä koetaan kauniina ja miellyttävänä, on psykologisesti kiinnostava kysymys. Työllä on myös merkitystä teollisuuteen kameroiden kuvanlaadun kehittämisessä. Väitöskirja sisältää kuusi julkaisua, joissa tarkastellaan aihetta eri näkökulmista. I. julkaisussa kehitettiin sovellus keräämään ihmisten antamia arvioita esitetyistä kuvista tutkijoiden vapaaseen käyttöön. Se antoi mahdollisuuden testata standardoituja kuvanlaadun arviointiin kehitettyjä menetelmiä ja kehittää niiden pohjalta myös uusia menetelmiä luoden perustan myöhemmille tutkimuksille. II. julkaisussa kehitettiin uusi kuvanlaadun arviointimenetelmä. Menetelmä hyödyntää sarjallista kuvien esitystapaa, jolla muodostettiin henkilöille mielikuva kuvien laatuvaihtelusta ennen varsinaista arviointia. Tämän todettiin vähentävän tulosten hajontaa ja erottelevan pienempiä kuvanlaatueroja. III. julkaisussa kuvaillaan tietokanta, jossa on 188 henkilön 480 kuvasta antamat laatuarviot ja niihin liittyvät kuvatiedostot. Tietokannat ovat arvokas työkalu pyrittäessä kehittämään algoritmeja kuvanlaadun automaattiseen arvosteluun. Niitä tarvitaan mm. opetusmateriaalina tekoälyyn pohjautuvien algoritmien kehityksessä sekä vertailtaessa eri algoritmien suorituskykyä toisiinsa. Mitä paremmin algoritmin tuottama ennuste korreloi ihmisten antamiin laatuarvioihin, sen parempi suorituskyky sillä voidaan sanoa olevan. IV. julkaisussa esitellään tietokanta, jossa on 210 henkilön 234 videoleikkeestä tekemät laatuarviot ja niihin liittyvät videotiedostot. Ajallisen ulottuvuuden vuoksi videoärsykkeiden virheet ovat erilaisia kuin kuvissa, mikä tuo omat haasteensa videoiden laatua arvioiville algoritmeille (VQA). Aikaisempien tietokantojen ärsykkeet on muodostettu esimerkiksi sumentamalla yksittäistä kuvaa asteittain, jolloin ne sisältävät vain yksiulotteisia vääristymiä. Nyt esitetyt tietokannat poikkeavat aikaisemmista ja sisältävät useita samanaikaisia vääristymistä, joiden interaktio kuvanlaadulle voi olla merkittävää. V. julkaisussa esitellään kuvanlaatuympyrä (image quality wheel). Se on kuvanlaadun käsitteiden sanasto, joka on kerätty analysoimalla 146 henkilön tuottamat 39 415 kuvanlaadun sanallista kuvausta. Sanastoilla on pitkät perinteet aistinvaraisen arvioinnin tutkimusperinteessä, mutta niitä ei ole aikaisemmin kehitetty kuvanlaadulle. VI. tutkimuksessa tutkittiin, kuinka arvioitsijoiden antamat käsitteet vaikuttavat kuvien laadun arviointiin. Esimerkiksi kuvien arvioitu terävyys tai luonnollisuus auttaa ymmärtämään laadunarvioinnin taustalla olevia päätöksentekoprosesseja. Tietoa voidaan käyttää esimerkiksi kuvan- ja videonlaadun arviointialgoritmien (I/VQA) kehitystyössä

Perceptual Image Quality Of Launch Vehicle Imaging Telescopes

A large fleet (in the hundreds) of high quality telescopes are used for tracking and imaging of launch vehicles during ascent from Cape Canaveral Air Force Station and Kennedy Space Center. A maintenance tool has been development for use with these telescopes. The tool requires rankings of telescope condition in terms of the ability to generate useful imagery. It is thus a case of ranking telescope conditions on the basis of the perceptual image quality of their imagery. Perceptual image quality metrics that are well-correlated to observer opinions of image quality have been available for several decades. However, these are quite limited in their applications, not being designed to compare various optical systems. The perceptual correlation of the metrics implies that a constant image quality curve (such as the boundary between two qualitative categories labeled as excellent and good) would have a constant value of the metric. This is not the case if the optical system parameters (such as object distance or aperture diameter) are varied. No published data on such direct variation is available and this dissertation presents an investigation made into the perceptual metric responses as system parameters are varied. This investigation leads to some non-intuitive conclusions. The perceptual metrics are reviewed as well as more common metrics and their inability to perform in the necessary manner for the research of interest. Perceptual test methods are also reviewed, as is the human visual system. iv Image formation theory is presented in a non-traditional form, yielding the surprising result that perceptual image quality is invariant under changes in focal length if the final displayed image remains constant. Experimental results are presented of changes in perceived image quality as aperture diameter is varied. Results are analyzed and shortcomings in the process and metrics are discussed. Using the test results, predictions are made about the form of the metric response to object distance variations, and subsequent testing was conducted to validate the predictions. The utility of the results, limitations of applicability, and the immediate ability to further generalize the results is presented

Subjective Image Quality Assessment of Digitally Printed Images

Smartphones have become ingrained in our daily activities, driving their cameras to become better with every generation. As more and more images are being taken by cell phones it has become increasingly important to assess the quality of the images taken by different phones. While many cell phone images are only viewed electronically, many images also get transformed into printed images, especially photo-books, as digital printing gets better and cheaper compared to traditional printing processes. The gap between electronic image and printed image in shrinking rapidly and it becomes important to study the transition of images from screen to paper. The main goal of this research was to perform a rank order experiment for assessing cell phone image capture quality that translates to printed images via several different digital printers. It was of interest to investigate whether the overall image quality on displays correlates well with printed image quality. The important aspect was to study was to observe if there is a loss of image quality due to different digital printers

Scene-Dependency of Spatial Image Quality Metrics

This thesis is concerned with the measurement of spatial imaging performance and the modelling of spatial image quality in digital capturing systems. Spatial imaging performance and image quality relate to the objective and subjective reproduction of luminance contrast signals by the system, respectively; they are critical to overall perceived image quality. The Modulation Transfer Function (MTF) and Noise Power Spectrum (NPS) describe the signal (contrast) transfer and noise characteristics of a system, respectively, with respect to spatial frequency. They are both, strictly speaking, only applicable to linear systems since they are founded upon linear system theory. Many contemporary capture systems use adaptive image signal processing, such as denoising and sharpening, to optimise output image quality. These non-linear processes change their behaviour according to characteristics of the input signal (i.e. the scene being captured). This behaviour renders system performance “scene-dependent” and difficult to measure accurately. The MTF and NPS are traditionally measured from test charts containing suitable predefined signals (e.g. edges, sinusoidal exposures, noise or uniform luminance patches). These signals trigger adaptive processes at uncharacteristic levels since they are unrepresentative of natural scene content. Thus, for systems using adaptive processes, the resultant MTFs and NPSs are not representative of performance “in the field” (i.e. capturing real scenes). Spatial image quality metrics for capturing systems aim to predict the relationship between MTF and NPS measurements and subjective ratings of image quality. They cascade both measures with contrast sensitivity functions that describe human visual sensitivity with respect to spatial frequency. The most recent metrics designed for adaptive systems use MTFs measured using the dead leaves test chart that is more representative of natural scene content than the abovementioned test charts. This marks a step toward modelling image quality with respect to real scene signals. This thesis presents novel scene-and-process-dependent MTFs (SPD-MTF) and NPSs (SPDNPS). They are measured from imaged pictorial scene (or dead leaves target) signals to account for system scene-dependency. Further, a number of spatial image quality metrics are revised to account for capture system and visual scene-dependency. Their MTF and NPS parameters were substituted for SPD-MTFs and SPD-NPSs. Likewise, their standard visual functions were substituted for contextual detection (cCSF) or discrimination (cVPF) functions. In addition, two novel spatial image quality metrics are presented (the log Noise Equivalent Quanta (NEQ) and Visual log NEQ) that implement SPD-MTFs and SPD-NPSs. The metrics, SPD-MTFs and SPD-NPSs were validated by analysing measurements from simulated image capture pipelines that applied either linear or adaptive image signal processing. The SPD-NPS measures displayed little evidence of measurement error, and the metrics performed most accurately when they used SPD-NPSs measured from images of scenes. The benefit of deriving SPD-MTFs from images of scenes was traded-off, however, against measurement bias. Most metrics performed most accurately with SPD-MTFs derived from dead leaves signals. Implementing the cCSF or cVPF did not increase metric accuracy. The log NEQ and Visual log NEQ metrics proposed in this thesis were highly competitive, outperforming metrics of the same genre. They were also more consistent than the IEEE P1858 Camera Phone Image Quality (CPIQ) metric when their input parameters were modified. The advantages and limitations of all performance measures and metrics were discussed, as well as their practical implementation and relevant applications

Better Images : Understanding and Measuring Subjective Image-Quality

The objective in this thesis was to examine the psychological process of image-quality estimation, specifically focusing on people who are naïve in this respect and on how they estimate high-quality images. Quality estimation in this context tends to be a preference task, and to be subjective. The aim in this thesis is to enhance understanding of viewing behaviour and estimation rules in the subjective assessment of image-quality. On a more general level, the intention is to shed light on estimation processes in preference tasks. An Interpretation-Based Quality (IBQ) method was therefore developed to investigate the rules used by naïve participants in their quality estimations. It combines qualitative and quantitative approaches, and complements standard methods of image-quality measurement. The findings indicate that the content of the image influences perceptions of its quality: it influences how the interaction between the content and the changing image features is interpreted (Study 1). The IBQ method was also used to create three subjective quality dimensions: naturalness of colour, darkness and sharpness (Study 2). These dimensions were used to describe the performance of camera components. The IBQ also revealed individual differences in estimation rules: the participants differed as to whether they included interpretation of the changes perceived in an image in their estimations or whether they just commented on them (Study 4). Viewing behaviour was measured to enable examination of the task properties as well as the individual differences. Viewing behaviour was compared in two tasks that are commonly used in studies on image-quality estimation: the estimation of difference and the estimation of difference in quality (Study 3). The results showed that viewing behaviour differed even in two magnitude-estimation tasks with identical material. When they were estimating quality the participants concentrated mainly on the semantically important areas of the image, whereas in the difference-estimation task they also examined wider areas. Further examination of quality-estimation task revealed individual differences in the viewing behaviour and in the importance these viewing behaviour groups attached to the interpretation of changes in their estimations (Study 4). It seems that people engaged in a subjective preference-estimation task use different estimation rules, which is also reflected in their viewing behaviour. The findings reported in this thesis indicate that: 1) people are able to describe the basis of their quality estimations even without training when they are allowed to use their own vocabulary; 2) the IBQ method has the potential to reveal the rules used in quality estimation; 3) changes in instructions influence the way people search for information from the images; and 4) there are individual differences in terms of rules and viewing behaviour in quality-estimation tasks.Tämä väitöskirja käsittelee subjektiivista kuvanlaadun arviointiprosessia, etenkin keskittyen kuvanlaadun arvioinnin suhteen kouluttamattomien ihmisten korkea laatuisten kuvien arviointiin. Kuvanlaadulla tarkoitetaan tässä kuvan prosessointiin liittyviä tekijöitä. Tavoitteena on lisätä ymmärrystä kuvanlaadun arviointiprosessista ja sen mittaamisesta. Kuvanlaadun arviointiprosessissa on yleisesti keskitytty saamaan yksi arvio laadusta tai yksi arvio jollain etukäteen määritellyllä skaalalla. Tällöin emme tiedä mihin kouluttamaton arvioitsija olisi kiinnittänyt huomionsa ja millä perusteilla hän olisi kuvaa arvioinut. Tätä selvittämään kehitimme menetelmän, jolla voimme tarkastella ihmisten arvioissaan käyttämiä perusteita. Ihmiset kuvailivat perusteita vapaasti ja kun he saivat käyttää omaa sanastoaan, he olivat myös johdonmukaisia arvioissaan. Tätä menetelmää käytettiin myös selvittämään subjektiivisia kuvanlaatu-ulottuvuuksia, joita olivat värien luonnollisuus, tummuus ja tarkkuus. Toinen osa väitöskirjaa käsittelee kuvanlaadun arviointitehtävää prosessina. Selvitimme miten pieni muutos koehenkilöille annetussa ohjeistuksessa muuttaa heidän tapaansa katsella kuvaa heidän tehdessä siihen liittyviä arvioita. Tehtävänä oli kahdessa kuvassa näkyvien erojen arviointi joko erojen suuruuden tai kuvanlaadun erojen mukaan. Kuvanlaatua arvioitaessa huomio kiinnittyi enemmän kohtiin, jotka olivat semanttisesti merkityksellisiä, kun eroja arvioitaessa laajempi alue otettiin huomioon. Tarkastelimme myös kuvanlaadunarviointeihin liittyviä yksilöiden välisiä eroja. Koehenkilöt pystyttiin jakamaan kolmeen ryhmään heidän katselutapojensa perusteella. Nämä katselutaparyhmät erosivat toisistaan myös siinä kuinka paljon he käyttivät arvioinneissaan perusteina vaikutelmia, jotka syntyivät kuvanlaadun muutosten pohjalta. Toiset keskittyivät arvioimaan kuvanlaatua siihen liittyvien attribuuttien mukaan, kun toiset käyttivät perusteina näiden attribuuttien kuvan viestiin synnyttämiä vaikutelmia. Korkean kuvanlaadun arvioinnissa on usein kyseessä mieltymyksiin perustuva laadun arviointi. Tällöin on tärkeää antaa ihmisten käyttää omia käsitteitään, sekä ottaa huomioon että pienimmätkin tekijät, kuten sanavalinnat kysymyksissä ja ihmisten väliset eroavuudet, vaikuttavat arviointeihin. Tämä väitöskirja antaa eväitä tarkastella arviointiprosessia

Blur-specific image quality assessment of microscopic hyperspectral images

Hyperspectral (HS) imaging (HSI) expands the number of channels captured within the electromagnetic spectrum with respect to regular imaging. Thus, microscopic HSI can improve cancer diagnosis by automatic classification of cells. However, homogeneous focus is difficult to achieve in such images, being the aim of this work to automatically quantify their focus for further image correction. A HS image database for focus assessment was captured. Subjective scores of image focus were obtained from 24 subjects and then correlated to state-of-the-art methods. Maximum Local Variation, Fast Image Sharpness block-based Method and Local Phase Coherence algorithms provided the best correlation results. With respect to execution time, LPC was the fastestBlur-specific image quality assessment of microscopic hyperspectral imagespublishedVersio