[NHCOLL-L:5487] RE: Colour of thin section images

[Burkhalter, Roger J.]

We have taken good images of clastic and carbonate thin sections by minimizing variables and using camera raw images and a custom camera profile in Adobe Lightroom for processing. We use a trinocular petrographic microscope with a microscope/camera adapter for a plain slr camera, in this case a Canon dslr. In our setting, we use color temperature (not white balance) matched to the light source, keep the light source at maximum, adjusting light input through the field diaphragm and condenser. The light source at maximum is critical as lower settings reduce the color temperature on typical tungsten halogen lamps resulting in a color shift to orange.  In my experience, color problems are mostly the result of light source temperature issues based on the microscope lamp intensity control. By using camera raw image capture, adjustments can be post-processed to optimum colors and those settings saved as a camera profile.  If the settings used are consistent, the profile can be used for images batch processing.  This should not change with the microscope's petrologic analyzer or Bertrand lens.

These options work for us, your equipment may be far different (factory ccd camera, etc.). I am not aware of a color calibration slide for petrographic images, I would be grateful to hear if one exists.

Roger

Roger J Burkhalter

Collection Manager

Department of Invertebrate Paleontology

Division of Collections and Research

Sam Noble Oklahoma Museum of Natural History University of Oklahoma

2401 Chautauqua

Norman, OK 73072

Phone: 405-325-1097

Fax: 405-325-7699
www.snomnh.ou.edu<http://www.snomnh.ou.edu>



From: owner-nhcoll-l at lists.yale.edu [mailto:owner-nhcoll-l at lists.yale.edu] On Behalf Of Christian Baars
Sent: Thursday, June 09, 2011 6:38 AM
To: 'NHCOLL-L at LISTS.YALE.EDU'
Subject: [NHCOLL-L:5485] Colour of thin section images


Hi,

we are having slight issues with the colours of images captured using a digital camera from a petrological microscope. The colours on images of petrological thin sections are never quite like those seen through the eye pieces. This can be adjusted using Photoshop but if taking a large series of images this can be quite laborous; it would be better to capture the correct colours in the first place.

Capturing images from stereomicroscopes we use a colour chart to calibrate the camera and to do a white balance prior to taking photos. With a petrological microscope this is obviously not possible, but I am wondering whether the principle may be.

Does anyone use a thin section with a standard material that appears to be white under the petrological microscope (plain polarized light)? Using simply a clear glass slide is not an option as we would just be calibrating the camera against the colour of the light from the lamp which is not necessarily white. Instead, we are looking for a material that we can use to make up a standard thin section for setting up a white balance.

Any ideas would be gratefully appreciated.

Kind regards
Christian




Dr Christian Baars
Department of Geology
National Museum Wales
Cathays Park
Cardiff CF10 3NP
UK
Telephone: 0044 (0)29 2057 3352





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