Evaluation of a modified sinar 54M digital camera at the National Gallery of Art, Washington DC during April, 2005

On April 26 – 27 2005, the RIT team brought their prototype Sinar 54M camera system to the National Gallery of Art’s Imaging Department. The team included Lawrence Taplin, Mitchell Rosen, and Roy Berns. RIT brought a spectroradiometer to measure the daylight fluorescent viewing illumination and if time allowed, NGA’s CRT display. They also brought a Macintosh G5 to control the camera and for image processing. NGA is using a production Sinar 54M. This enabled a direct comparison between NGA’s digital imaging workflow and the RIT workflow. Both cameras used the same lighting, Broncolor pulsed Xenon, lighting geometry, and photography studio. A set of test targets was imaged by each camera system. In addition, Matisse’s Pot of Geraniums, previously imaged by RIT using their 31-channel spectral camera,1-3 was also imaged. The digital masters from each camera system were converted to an output profile for an Epson Ultrachrome inkjet printer. One-to-one prints were made for the Matisse painting and compared with the actual painting under the daylight fluorescent viewing environment. The RIT prototype camera and the print comparison were evaluated by NGA staff from the imaging, conservation, and finance departments

Practical spectral capture systems for museum imaging

Spectral imaging systems for capturing museum artwork have not moved beyond the research laboratory. System components and their selection criteria necessary to assemble a complete system are explored in this paper categorically. The final system is practical if it meets the criteria of speed cost and accuracy necessary to act as a direct replacement for the traditional RGB based digital imaging systems in museum photo studios. It is hoped that the advantages of spectral imaging will be widely recognized and adopted once a practical system is available

A prototype calibration target for spectral imaging

A prototype calibration target was designed and tested for spectral imaging that consisted of 14 samples, nine of which were derived from statistical analyses of artist paints and a five-step grey scale. This target was compared with those commonly used when calibrating spectral-imaging systems. An Esser TE221 scanner target, GretagMacbeth ColorChecker DC, GretagMacbeth ColorChecker Color Rendition Chart, and the prototype target were used as both calibration and verification targets using a modified commercial color-filter-array digital camera as a spectralimaging device. When evaluating a verification target made from 30 different pigments, the prototype target had equivalent performance. Thus for spectral imaging, the spectral properties are more important than the number of samples or its colorimetric range of colors

Lightness Dependencies and the Effect of Texture on Suprathreshold Lightness Tolerances

A psychophysical experiment was performed to determine the effects of lightness dependency on suprathreshold lightness tolerances. Using a pass/fail method of constant stimuli, lightness tolerance thresholds were measured using achromatic stimuli centered at CIELAB L* = 10, 20, 40, 60, 80, and 90 using 44 observers. In addition to measuring tolerance thresholds for uniform samples, lightness tolerances were measured using stimuli with a simulated texture of thread wound on a card. A texture intermediate between the wound thread and the uniform stimuli was also used. A computer-controlled CRT was used to perform the experiments. Lightness tolerances were found to increase with increasing lightness of the test stimuli. For the uniform stimuli this effect was only evident at the higher lightnesses. For the textured stimuli, this trend was more evident throughout the whole lightness range. Texture had an effect of increasing the tolerance thresholds by a factor of almost 2 as compared to the uniform stimuli. The intermediate texture had tolerance thresholds that were between those of the uniform and full-textured stimuli. Transforming the results into a plot of threshold vs. intensity produced results that were more uniform across the three conditions. This may indicate that CIELAB is not the best space in which to model these effects

Modifications of a sinarback 54 digital camera for spectral and high-accuracy colorimetric imaging: simulations and experiments

A search technique was used to identify sets of colored glass filters that could be placed in the optical path of the Sinarback 54 camera system resulting in improved color accuracy compared with a production unit and the ability to perform spectral estimation. A green and blue filter, each a pair of filters, were identified and constructed from Schott glass. RGB images were collected through these two filters resulting in six image planes. Using the Gretag Macbeth ColorChecker DC and a custom target of blue artist pigments, a transformation was derived that converted digitally flat-fielded and photometrically-linearized camera signals to estimated spectral reflectance factor. The combination of using these two filter “sandwiches” and appropriate mathematics resulted in more than a twofold improvement in color and spectral accuracy compared with the production camera. The average colorimetric and spectral performance is shown in the following bar graphs for the calibration targets and independent-verification targets, the Esser TE221 test chart, a custom target of artist pigments made using the Gamblin Conservation Colors, and the traditional GretagMacbeth ColorChecker Color Rendition chart. These results indicate that it is possible to achieve excellent color accuracy and acceptable spectral accuracy using a color-filter array sensor

Exploring the color inconstancy of prints

The color inconstancy of prints is related to the ink spectral properties and the lookup table for multiink printing systems. In this paper, color inconstancy was investigated for several ink-jet printers based on their ink set and the default lookup tables. A virtual model for each printer was created to determine the range of color inconstancy that a specific ink set could achieve. The color inconstancy performance of each default lookup table was evaluated by evaluating the color inconstancy of a printed test target. The optimum combinations of three- and four-chromatic inks were investigated to minimize the color inconstancy and keep a relative large color gamut simultaneously. The results showed that the color inconstancy can be decreased significantly without compromising the reproduction colorimetric accuracy. Moreover the color inconstancy can be improved by appropriate ink design

Spectral imaging using a commercial colour-filter array digital camera

A multi-year research programme is underway to develop and deliver spectral-based digital cameras for imaging cultural heritage at the National Gallery of Art, Washington DC, and the Museum of Modern Art, New York. The cameras will be used for documentation, production imaging, and conservation science. Three approaches have undergone testing: a liquid-crystal tunable filter (LCTF) coupled with a monochrome camera, a six-position filter wheel containing absorption filters coupled with a monochrome camera, and a two-position filter slider containing absorption filters coupled with a colour-filter array (CFA) colour camera. The last approach is the most practical as it uses conventional digital photography methodologies and equipment and can easily be incorporated into existing museum workflows. A virtual camera model was created that predicted camera signals from incident radiation and was used to design a pair of absorption filters. The filters were fabricated and tested using a commercial CFA digital camera. Our first experiments have been very promising: Average accuracy was under 1 CIEDE2000 and about 1.5 per cent RMS for both calibration and verification data. This level of performance was superior to our other, more complex approaches

Advances in multispectral and hyperspectral imaging for archaeology and art conservation

Multispectral imaging has been applied to the field of art conservation and art history since the early 1990s. It is attractive as a noninvasive imaging technique because it is fast and hence capable of imaging large areas of an object giving both spatial and spectral information. This paper gives an overview of the different instrumental designs, image processing techniques and various applications of multispectral and hyperspectral imaging to art conservation, art history and archaeology. Recent advances in the development of remote and versatile multispectral and hyperspectral imaging as well as techniques in pigment identification will be presented. Future prospects including combination of spectral imaging with other noninvasive imaging and analytical techniques will be discussed

Non–housestaff medicine services in academic centers: Models and challenges

Non–housestaff medicine services are growing rapidly in academic medical centers (AMCs), partly driven by efforts to comply with resident duty hour restrictions. Hospitalists have emerged as a solution to providing these services given their commitment to delivering efficient and high-quality care and the field's rapid growth. However, limited evidence is available on designing these services, including the similarities and differences of existing ones. We describe non–housestaff medicine services at 5 AMCs in order to share our experiences and outline important considerations in service development. We discuss common challenges in building and sustaining these models along with local institutional factors that affect decision making. Keys to success include ensuring an equitable system for scheduling and staffing, fostering opportunities for scholarly activities and academic promotion (defining the “academic hospitalist”), and providing compensation that supports recruitment and retention of hospitalists. With further work hour restrictions expected in the future and increased requests for surgical comanagement, the relationship between AMCs and hospitalists will continue to evolve. To succeed in developing hospitalist faculty who follow long careers in hospital medicine, academic leadership must carefully plan for and evaluate the methods of providing these clinical services while expanding on our academic mission. Journal of Hospital Medicine 2008;3:247–255. © 2008 Society of Hospital Medicine.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/60235/1/311_ftp.pd