Photo Stitching

Photo stitching is the process of combining multiple overlapped photographs into a single larger image.  This is normally accomplished with digital photographs and specialized computer software.  The technology was examined to determine if it was appropriate for creating photomosaics.  At that time, many of the stitching applications were not available for Macintosh computers.  Others were only capable of producing panoramas from images taken by a camera rotated around a single point.

The stitching programs used pairs of control points that identified the same locations on adjoining photographs.  The pairs of points could be manually selected by visual inspection, or automatically selected by several of the computer applications.  The best results were achieved by manually picking the control points.  However, the lack of sharp corners and straight lines on buildings in Pompeii made the identification of matching points difficult.  Color control between multiple photographs was also unsatisfactory.

The most accurate and best quality photomosaics for this project were produced by using Photoshop image editing software to manually combine digital photographs over an orthographic control background drawing.

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Photomosaic Assembly

The final step was to combine the multiple photographic images and the orthographic control background drawings into photomosaics.

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– The work was accomplished on an Apple Mac Pro Dual Core Intel Xeon (System 10.4.11).

Technical Standards - The previously developed criteria were utilized for the work:

  • Control background and photomosaic resolution at 300 pixels per inch.
  • Control background and photomosaic scale at 1:25.
  • Photoshop (versions CS, CS2, CS3 and CS4) image editing software.

Work sequence – The photomosaics were produced using the following procedures:

  • Two digital file folders were created and saved as North and South to indicate the two sides of the street.
  • A master folder for each insula was created, named and placed into the appropriate North or South folder.
  • The original photographs of each insula were collected and placed into the master folders.
  • A new folder was created and named “Duplicates” into which copies of the original photographs were placed.  These photographs were used to create the photomosaic, leaving the originals untouched.  This folder was then placed into the Master folder.
  • A new Photoshop document was created using the 300 ppi control background drawing as the base layer.
  • The series of photographs for the insula were opened in Bridge (an image browser) and the photograph of the Kodak Q-13 Color Separation Guide was selected and opened in Photoshop.  Its parameters were adjusted until the screen image colors matched a Kodak Q-13 placed next to the monitor.
  • In Bridge, the color adjustment settings of the image of the Kodak card were then used to batch modify the color parameters of all of the photographs of the facade.
  • Each facade photograph was sequentially opened in Photoshop and positioned over the background on a separate layer.
  • Each new photo was placed so that it overlapped the previous image.
  • The opacity of the latest image was reduced to approximately 50% so that the previous photograph underneath could be seen.
  • The size of the photograph was checked, and then it was moved to match any details (such as windows, doors, cracks, holes, etc.) with the previous image below and with the control background drawing on the base layer.
  • After the photograph was satisfactorily sized and placed with the adjacent image, the unwanted parts of both were removed using the Eraser tool, and the opacity returned to 100%.
  • Overlaps were blended and any final adjustments were made to the color and contrast of the newest image to match all those that had been previously incorporated.
  • A scale bar, title and date were placed on the image.
  • The final photomosaic with all layers was saved and backed up.
  • The final photomosaic was then “Saved As” using a different name, and the layers flattened into one in order to decrease the image file size.
  • Copies of the flattened photomosaic were saved as other file formats (TIFF, JPEG, etc.) for distribution and use.

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The completed images, and other related information about the city blocks, are presented in the section entitled Photomosaics.

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