Paleonet: Orthochromatic images
e_bonino at yahoo.it
Sat Mar 26 09:12:41 GMT 2011
thank you very much for the huge quantity of replies and suggestions received in these days.
Indeed appear that modern technologies of image acquisition and processing can bypass the use of filters that were common only some years ago (thank you to Mark, Aaron and Eric Pirard from the Liège University, Belgium).
A CCD sensor allowing to acquire raw images at more than 8bit (12, 16...), is preferable to extract more useful informations from a picture.
Interesting can be to know the distribution of the wavelengths acquired by the red, green, blue cells of the CCD used.
The use of polarized light (two crossed filters, more or less like in mineralogical microscopy, positioned one in front of the light source and another in front of the optics) give excellent results when the matrix is dark (like for Burgess Shale fauna, as suggested by Martin Smith from the Royal Ontario Museum), and increase remarkably the contrast, for example, in Chengjiang's fossils.
I suppose that the use of "dark light" (Ultraviolet light) can give, in certain conditions and mineralogical composition, interesting results, as suggested by Maurizio Gnoli from the University of Modena and Reggio Emilia (Italy).
Similarly, acquisitions in the near Infra-red domain (but I don't think that actual all-public camera's are "sensible" to the NIR) can be explored.
Anyway, many things to be explored and to develop.
GIS Specialist - Geologist at KEYOBS SA, Liège, Belgium
Museum Curator at the Back to the Past Museum, Cancun, Mexico
...and some of my dioramas at FossiliVeraciand Paleonet
Da: Mark R. Besonen <mark.besonen at tamucc.edu>
A: e_bonino at yahoo.it
Cc: paleonet at nhm.ac.uk; "Besonen, Mark R." <mark.besonen at tamucc.edu>
Inviato: Venerdì 25 Marzo 2011 23:59
Oggetto: Re: Paleonet: Orthochromatic images
Maybe I have interpreted your message wrong, but many image manipulation programs allow you to take a color image (the composite of red-green-blue channels, i.e. RGB), and only examine one or two of the color channels at a time. For certain, you sometimes do have much better contrast using one/two of the channels vs. a composite RGB image. Image manipulation programs that will let you do something like this include Adobe Photoshop, and the open source GIMP (http://www.gimp.org/), among many others.
There are also a whole range of programs meant more directly for image analysis (quantitative measurements and manipulations) vs. simple manipulation/touchup. These programs will generally let you take the process a whole lot further, and you can do explicit mathematical manipulations on the individual channels (like adding two, dividing one by another, etc.) to really pull out contrast. An open source program that can do this is ImageJ (http://rsb.info.nih.gov/ij/). ImageJ has a robust user community, and with a little practice, you can easily automate processes with its batch/scripting language.
I have attached an image of an arkose split into red, green, blue, and a green+blue composite channel. As you can see, the G+B channel really pulls out the contrast. Hope this gives you some inspiration!
On 3/23/2011 6:35 AM, enrico bonino wrote:
> Dear all
> I'm searching for a method that allow to acquire images with a digital
> camera (Fujifilm filmpix S2Pro) that can emulate the old Orthochromatic
> Orthochromatic films block the red wavelength and are sensitive to blue
> and green only, giving a great contrast when red colors are present in
> the image.
> These films are used in Xiangguang & Bergström (1997), Arthropods of the
> Lower Cambrian Chengjiang fauna, southwest China, in Fossils & Strata
> n°45, to improve the contrast of some lower Cambrian Chengjiang arthropods.
> This methods don't need the immersion of the sample in Toluene or Xylene
> alcohols, and it is very useful when the matrix (and this is the case)
> is soft, like marls and clays.
> Chengjiang fossils are generally covered by a thin Iron oxide layer, and
> this technique allow to increase the contrast between the gray-yellow
> matrix and the reddish fossil.
> Looking at some filters that have the same spectral behavior, I've found
> that the cyan Kodak Wratten gelatine filters 44 and 44A
> (http://en.wikipedia.org/wiki/Wratten_number and
> for the transmittance curve) are able to give the nearly same result of
> the old and practically unavailable orthochromatic films.
> There is someone that has developed similar techniques and digital image
> processing methods to increase the contrast using peculiar filters?
> Thank you,
> Enrico Bonino
> Paleonet mailing list
> Paleonet at nhm.ac.uk
-- Mark R. Besonen
Assistant Professor, Geology Program
Department of Physical and Environmental Sciences
Texas A&M University - Corpus Christi
6300 Ocean Drive, Unit 5892
Corpus Christi, TX 78412
office: HRI 103
tel: +1.361.825.2043 (office)
tel: +1.361.825.2039 (lab)
e-mail: mark.besonen at tamucc.edu
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