RPS Imaging Science Group

Back in Minneapolis after about 10 years. Last time I was here it was to support the Curtis Centennial Project with some work to reproduce the work of the American photographer Edward S Curtis. Working with large photographic glass plates we created some stunning imagery – see http://www.edwardcurtis.com/goldtone/gt.html for further detail.
Not an easy one to reproduce by inkjet!

With all the recent attention on fever screening there has been a lot of column inches devoted to remote thermographic imaging.
There is more to this technique than airport screening. The European Southern Observatory has an infrared spectrograph called CRIRES (CRyogenic InfraRed Echelle Spectrograph), fitted to the Very Large Telescope in Chile. They have used this to measure the current temperature of the lower atmosphere of Pluto. At -180°C this is substantially warmer than the surface. This is believed to be because sunlight evaporates some of the surface ices, warming the atmosphere but cooling the surface. See http://www.eso.org/public/outreach/press-rel/pr-2009/pr-08-09.html for more details.
Now there’s a really remote example!

I spent the last week in Washington DC at ISO Image Permanence standards meetings – see recent blog articles. Flying onwards my attention was drawn to an article in the May edition of Chemistry World “New dye design for solar cells” (see www.chemistryworld.org) . The article describes recent progress on the ruthenium based dyes used in dye sensitised solar cells. One of the issues with these compounds is their stability which is currently limited by the use of thiocyanate ligands on the central metal. While the thrust of this article is potential replacements for this (it is a chemistry journal) my eye was drawn to the current stability test time – 8000 hours. While this does not sound long it did occur to me that this community could benefit from the testing knowledge gained by the Image Permanence community!

The Hubble Space Telescope captured by STS125 ©NASA

Now that’s a big camera!
The STS125 (Atlantis) mission has been successful in replacing the Wide Field Planetary Camera 2(WFPC) in the Hubble Space Telescope with WFPC3. Described in the Washington newspapers as “as big as a piano” you can find a more scientific description on the Space Telescope Science Institute page http://www.stsci.edu/hst/wfc3/design/at_a_glance/ . The camera contains 2 detector systems. The one for the IR contains a 1MPixel HgCdTe detector sensitive out to around 1.8μm. The visible unit contains 2x 8MPixel sensors.
So no megapixel mania here! I look forward to seeing the first pictures!

The European Space Agency has successfully launched the Herschel Space Observatory. This instrument supports a huge infrared camera featuring the largest telescope mirror  launched into space. With a diameter of 3.5m it dwarfs the “mere” 2.4m mirror in Hubble. The camera also breaks new ground by using this phenomenal light gathering power to explore the far IR and sub-millimeter wavelengths (55-670µm). As a result it will image the thermal emissions of cooler structures than shorter wavelength systems – down to around 100K.
These wavelengths are slightly shorter than  those observed by microwave observatories such as Planck which was launched at the same time. They are also slightly longer than earlier infrared space-based observatories which has implications for the optics. As any “warm” object emits infrared the emissions from the optlcs can mask those of the objects themselves. As a result earlier space-based infrared observatories had both optlcs and detectors cooled by liquid Helium.
These longer wavelengths render dust clouds transparent, allowing these systems to image deeper into obscured areas of the Universe. This wavelength range also allows access to remote IR spectroscopy studies. Infrared spectra determinations I once conducted in an undergraduate laboratory can now be achieved on interstellar objects.
The aim of Herschel is to study star and galaxy formation. In the main these are difficult to image at visible wavelengths as they are usually embedded in clouds of cool dust and gas. In order to image such cool structures the imaging systems must be cooled to even lower temperatures. The detectors themselves are enclosed in a liquid Helium cryostat at around 4K. The main mirror optlcs remain at <100K behind a sunshade with the entire telescope parked at the outer (L2) Lagrange point over 1mio km from the thermal emissions of the Earth.
Because this huge optical chain is designed to run at such low temperatures it is impractical to test as a system before launch. Let’s hope we have learnt the lessons of Hubble!

The eye response functions

One of the creative attributes of Infrared photography is that it provides a different view on a scene to that perceived by the human visual system. The very term infrared (after red) suggests that it is the region of the spectrum that starts where the visual red finishes.
So where does infrared start and the visual region finish? The clue to this comes in the chart above. This shows the eye response function to 2 different light levels. The “photopic” line shows the combined response of the human eye under normal daylight light levels. It can be seen that the photopic response falls effectively to zero around 680nm so infrared occupies the region after this.
As a result of this pictures taken through filters that allow wavelengths to pass that are longer than 680nm record phenomena not noted by the naked eye, which is what makes it so interesting!
The chart above also reveals an interesting issues. At low light levels the eye fails to see in colour and moves to scotopic vision. As the curve in the chart reveals the eye sensitivity response moves to shorter wavelengths. If we were to consider the onset of “visual infrared” in this case it would be wavelengths above 600nm!
It would be an interesting project to take some images at wavelengths below 600nm and see how close they look to moonlight when rendered into a monochrome image. I feel a project coming on…
These curves are plotted from CIE standard data that can be found in a really useful resource from University College London – see http://www.cvrl.org/

The IS&T Archiving conference

In Washington DC for the ISO meetings on Image Permanence. In addition to these meetings this is a great opportunity to meet up with the Archiving community. Some of these people had just been along to the IS&T Archiving meeting and tell me that this was a great event this year. The programme looks good – see http://www.imaging.org/conferences/PDF_PROGRAMS/Archiving09_Prelim_Program.pdf . I look forward to doing a short review on this blog.
As the community was in town the Image Permanence Institute held a meeting of their Board of Advisors. I went along as an observer as they do some really good work – see http://www.imagepermanenceinstitute.org/ .
And finally off to my first IS&T Board Meeting. We are meeting up just outside of Washington DC so a hectic few days. But hopefully, a lot to write about!

I covered my interest in this meeting in an earlier entry. Some colleagues from the UK Displays and Lighting (UKDL) KTN went along and have kindly agreed to share their impressions with us.
The meeting was held in Dresden but UK interest were was represented by a joint stand between the UKDL, UK Trade and Investment and a consortium of organizations representing the development and exploitation organizations in the UK – see www.PlasticElectronicsUK.com. The “UK stand” was kept busy by a constant throughput of visitors interested in seeing what the UK could offer the plastic electronics community.
I was interested to hear of a number of key technologies on show. The first was particulate copper inks from Novacentrix. Rather like conventional photography the preferred technology for conductive inks has been silver based. Silver has a high conductivity it can be manufactured in the form of micro and nano particles for inclusion in ink formulations and its oxide is conductive. From an economic perspective, copper would be ideal as it has a conductivity close to silver and is significantly cheaper. Unfortunately, copper is readily oxidised and its oxide is non conductive. Past attempts to formulate conductive inks using copper particles have not been widely successful. Novacentrix appear to have made a breakthrough in this area and although their system appears to produce only thin conductive films it does appear to offer a welcome alternative.
There does appear to be space for the some of the particulate silver based technologies from photography. At the last IS&T Digital Fabrication conference there were a number of papers on technology utilising dry silver systems – see http://www.imaging.org/conferences/PDF_PROGRAMS/NIP24_DF2008_Prelim_Program.pdf
The other photo based technology on show in Dresden was the use of the Agfa PEDOT:PSS technology to produce conductive layers. They are now applying this to OLED lighting but I remember this technology for conductive layers for static control on photo base.
Life in these old photo technologies yet!

A modified Dialyte system from Wise & Hodgson (EOS reference below)

From the very earliest days of optical instruments the problems of chromatic aberration have been recognized. Judicious choice of material types in combination in compound elements in camera lenses and telescope and microscope objectives have largely solved these issues but at the expense of cost, size and weight. There are work-arounds. There is an early optical design called the Dialyte – see R Blakley, Dialyte-refractor design for self-correcting lateral color”, Opt. Eng. 42(2) 400–404 (2003). I was involved in the evolution of this a few years ago that resulted in a paper at the European Optical Society Topical Meeting on Advanced Imaging Techniques, Lille, France in September 2007 “Adapting novel consumer astronomical telescope designs for professional imaging”. However, all these designs involve compromise.
Some of these compromises are being revisited in an alternative approach. Workers at Samsung are using electronic imaging techniques to digitally remove or correct for chromatic aberration effects and have written a paper or this. They presented their work at the IS&T/SPIE 21st Annual Electronic Imaging Symposium earlier this year but the paper can currently be found under www.imaging.org/pubs/reporter/.
This current edition of The Reporter also has a review of this meeting. After my election as IS&T Conference VP I hope to connect more closely with this community. I have not yet done one of these meetings but they look good!