Understanding MSI Images

By Jacob W. Peterson and Leigh Ann Thompson

This May CSNTM has had the opportunity to attend a digital archiving conference in Portugal and digitize in Germany. The images captured during the Beuron expedition are now available in our digital library. In the entry for GA 0197, we include a series of images captured by our MSI equipment that we obtained in May 2018. See the above link to our newest entry in the digital library and see below for an explanation of the different images you will see. Head over to the library page to view this new entry and the fascinating results of MSI.

What Kinds of Images Does MSI Produce?

Multispectral imaging equipment captures images at different and specific wavelengths of light. A series of images for each page we digitize reflects what each band of light captures. These different bands will bring forward different features of manuscripts based on what the materials, depth and layers reflect better or worse with the utilized wavelength and filter.

The series of images that reflect what each band of light captures taken together produce a “composite image.” This image is first in the series for each page, and is in color, displaying what the naked eye would see if viewing the manuscript in person. For example, see the image of GA 0197 below.

0197 1a composite

Basically all that you can see if the overtext of a Typikon. However, the undertext becomes especially visible under the 365 nanometer ultraviolet light with a UV-pass:

0197 undertext

The Physics of MSI

The visible light spectrum–what you and I can see with our eyes–is only a small portion of the electromagnetic spectrum seen in the image below.

Light wavelengths spectrum

The electromagnetic spectrum records the wavelengths in nanometers (nm) of the various types of waves floating around in the air—from gamma rays to radio waves. In our multispectral setup, we are only interested in the visible spectrum and the two surrounding divisions of ultraviolet and infrared light. Our equipment is capable of producing light from 365nm in the UV spectrum, through the visible light spectrum, and up to 940nm in the infrared spectrum.

Viewing MSI Images in the CSNTM Library

When you are looking at the images produced from each of the individual bands, you will see the composite image first, followed by 25 monochrome images. After you click on a particular thumbnail, the image description will give you information such as this:

MSI filename

What you are seeing in the image name field is the GA number of the manuscript, the image sequence number, and finally the multispectral information. The following is a list of the 25 different images captured in one session:

  • MB365UV_0011 – Mains, 365nm, ultraviolet light
  • MB400UV_0012 – Mains, 400nm, ultraviolet light
  • MB420VI_0001 – Mains, 420nm, violet light
  • MB450RB_0002 – Mains, 450nm, royal blue light
  • MB470LB_0003 – Mains, 470nm, light blue light
  • MB505CN_0004 – Mains, 505nm, cyan light
  • MB530GN_0005 – Mains, 530nm, green light
  • MB560LI_0006 – Mains, 560nm, yellow light
  • MB590AM_0007 – Mains, 590nm, amber light
  • MB615RO_0008 – Mains, 615nm, red-orange light
  • MB630RD_0009 – Mains, 630nm, red light
  • MB655DR_0010 – Mains, 655nm, dark red light
  • MB735IR_0013 – Mains, 735nm, infrared light
  • MB850IR_0014 – Mains, 850nm, infrared light
  • MB940IR_0015 – Mains, 940nm, infrared light
  • W365B47_0020  – Wheels, 365nm, ultraviolet light with blue filter
  • W365G58_0018 – Wheels, 365nm, ultraviolet light with green filter
  • W365O22_0023 – Wheels, 365nm, ultraviolet light with orange filter
  • W365R25_0016 – Wheels, 365nm, ultraviolet light with red filter
  • W365UVB_0022 – Wheels, 365nm, ultraviolet light with UV-block
  • W365UVP_0025 – Wheels, 365nm, ultraviolet light with UV-pass
  • W450B47_0021 – Wheels, 450nm, ultraviolet light with blue filter
  • W450G58_0019 – Wheels, 450nm, ultraviolet light with green filter
  • W450O22_0024 – Wheels, 450nm, ultraviolet light with orange filter
  • W450R25_0017 – Wheels, 450nm, ultraviolet light with red filter

As might be clear, everything that begins with a “W” indicates that there is some sort of filter being applied to the shot. Our system runs through 15 “main” images first, then the “wheel” apparatus attached to the camera cycles through 10 addtional combinations of lights and filters.

As you will notice, not every image is created equally. Some of the bands of light produce little of value while others reveal all kinds of information. Some patterns between types of images will be apparent (e.g. UV light works well with water damage), but what works well on one page in a manuscript may not be successful at revealing anything on the next page. All that to say, make sure you consult all of the images in the sequence.

What’s Next?

The next step for CSNTM will be the post-processing of these images. Through this, the various bands are manipulated and various processes are applied to help reveal as much of the text as possible. Once this has been completed, these images will be added to our online library.

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