Good Picture 2003: Assessing the Quality of Digital Images and Systems

An RPS Symposium

The Imaging Science Group of the RPS organised a tutorial seminar as part of the 150th Anniversary celebrations of the Society in an area of intense interest for image makers. It was held at the University of Westminster, London, on 17th December 2003.

Right: Opening the meeting, Mike Christianson

Listed below are details of the papers presented at this symposium. Some of the speakers have kindly agreed to allow us to publish the slides which accompanied their presentations. These can be viewed by clicking on the active links below.

Right: Choosing a camera, Mike Pointer

N.B. Click on either image for an enlarged view

Professor Ray Clark (RPS Past President): Wonders of Imaging: Past and Present
Drawing from the Society's Collection (founded in 1853), this talk will demonstrate early world class images and equipment. Coming forward to the present, advances in state of the art medical and scientific imaging will also be described and illustrated.

Professor Ralph Jacobson, University of Westminster: Image Quality: Meanings, Minefields and Mastery
This will be an essentially non-mathematical overview of various issues relating to image quality, including working definitions, transferability of concepts from conventional to digital systems, physical (objective) and psychophysical (subjective) measures. Advantages and pitfalls will be highlighted.

Dr. Rob Jenkin, University of Cranfield: "Fuzzy Duck!"
What determines how sharp images appear? Is it just number of pixels or film grain? How do we measure it? This talk introduces the concept and use of Modulation Transfer Function to evaluate imaging systems from a layman's perspective. Go on - add a graphic equalizer to your camera!

Professor Geoff Attridge, University of Westminster: Digital Cameras - Lovely Colour Isn't It?
This talk will outline the reproduction of colour by digital photography and will address the characterisation of digital cameras in terms of the "colorimetric accuracy of colour reproduction". Important limitations of colour reproduction will also be identified.

Dr. Mike Pointer, National Physical Laboratory: Digital Cameras - Choosing and Using
This talk will review the major decisions that must be made in order to choose a digital camera. The issues described will include the concepts of pixels, resolution and compression, as well as taking the picture, downloading the stored image, and viewing and editing the image.

Professor Robert Hunt, Colour Consultant: How To Make Pictures and Please People
The various ways in which pictures can be made by both subtractive and additive displays are reviewed. Systems using these displays are all limited by errors caused by incorrect camera spectral sensitivities, and by the limited gamuts of reproducible colors. Subtractive systems are further limited by the unwanted absorptions of their colorants. Pictorial images are usually assessed by comparison with memories of familiar objects. Because such objects vary considerably in color appearance, the tolerances in images of pictorial scenes are quite large; however, these variations tend to be smallest for hue and largest for colourfulness, so that hue is the most, and colourfulness the least, important attribute in imaging. Six possible different objectives are described: spectral, colorimetric, exact, equivalent, corresponding, and preferred. Possible reasons for preferring increased contrast in images are discussed.

Jim Aldridge, Home Office: Digital Images and the Criminal Justice System
The increasing use of digital images for evidence raises a number of issues for those who take, process and use the material as it passes through the CJS. A procedure has been published allowing images to be handled in a standardised way that complies with the rules of evidence. The paper will outline the procedure and examine some practical issues.

Dr. Sophie Triantaphillidou, University of Westminster: Archival Image Quality, Storage and Migration Strategies (0.9Mb Acrobat file)
The talk will introduce the processes involved in the digitisation, display and storage of image collections and archives. Description of device characterisation and calibration procedures will be discussed, along with the important issues of image encoding, file format, physical storage and data migration.