Digital Images and Seismic Design

Digital Images and Seismic Design
A new role for photographs in architecture and engineering

AIA Faculty Institute on Teaching Seismic Design
Berkeley CA, February 2-5, 1996
Last updated Thursday, February 1, 1996, at 5:09 PM Copyright © 1996, Kirk Martini

Overview
Availability
Enhancement
Annotation
Distribution
Integration with text

Overview

Digital images offer several advantages over conventional slides in for teaching and research in architecture and engineering. These advantages include:

Availability: There are now sources where images are available only in digital format, and cannot be obtained as conventional slides. Particularly important are sources such as the EqIIS system of the EERC Library which provides images free in the public domain.
Enhancement: Using image processing software, it is possible to enhance the contrast, color, and sharpness of a digital image for greater clarity. It is also possible to distort the fidelity to clarify important engineering features, such as digitally "bleaching" a dark slide to reveal details in the shadows. In addition, images can be cropped and manipulated to remove extraneous information.
Annotation: With digital images, it is possible to add text, symbols, transparent overlays, guidelines, and other annotation to highlight, explain, and analyze important features in an image.
Distribution: Unlike conventional slides, digital images can be distributed over the world wide web, so that they can be made accessible to any computer in the world that is connected to the web.
Integration with text: Using web documents, digital images can be easily combined with sketches and text which support and explain the image content. This document demonstrates this capability.

Availability

The EqIIS collection of the EERC Library is by far the best source of seismic and structural images on the web. FEMA maintains a very small site, although some of the images are instructive.

After the Kobe and Northridge events, many sites sprang up from news organizations and ordinary people with scanners and servers. The level of image quality and documentation for these sites is generally not very good, and many of the sites were short lived. There can also be copyright difficulties in using images from news organizations.

Here are some sample links:

Enhancement

There are several useful techniques for digital enhancement of images. The most important techniques are adjusting levels and sharpening. Cropping an image is also useful to remove extraneous information on the edges of an image, it is also possible, though not always ethical, to actually remove elements from a scene. The following is a series of examples illustrating these techniques.

Adjusting Levels

The thumbnail image below is linked to a downloaded page from the EqIIS Collection. Click on the image to see the information page, and then click on that page's thumbnail to see the full-sized image.

The effect of the weld damage on the paint is very difficult to see in the image because the slide is so dark. Compare that image to an image which has been enhanced by adjusting the exposure levels, shown in this comparison.

This example illustrates the ability to distort visual fidelity to clarify engineering features, and it raises an important issue concerning image enhancement. Effective image enhancement must address the question of how the image will be used. The enhanced image of the weld is very useful for identifying locations where the paint has flaked, but is may be much less useful for training someone to recognize such damage. Enhanced images can be used to represent situations that in fact never existed, and must be used with care.

Sharpening

The following comparison shows an image of the Olive View Hospital, downloaded from the EqIIS collection, with a version of the same image that has been sharpened, cropped, and scaled, along with a side-by-side comparison of portions of the images.

Cropping and scaling allow the image to focus on the primary subject, removing the landscaping and scenery in the foreground and periphery. Sharpening simply creates a clearer, better looking image; this can be important in images with fine detail.

Annotation

Digital images also allow the annotation of images with text, guidelines, overlays, and other graphic devices. Such annotation is not impossible with conventional images, but is extremely time consuming and expensive. With digital images, it is possible to create rich annotations working with a desktop computer.

The series of thumbnail images below use an image of an earthquake-damaged column to explain the concept of shear.

In addition to annotation with symbols, as illustrated with the force arrows, these images illustrate two useful techniques:

Masking: The gray mask in the second image helps to isolate the area in question. For this image, it identifies the free body on which the force arrows are acting in the third image. Without masking it would not be clear whether the arrows were intended to represent forces acting on the object or forces exerted by it.
Overlays: Semi-transparent overlays, as used in the third image, are useful for several purposes. As used above, the overlay clarifies the racking action resulting from shear, and allows the reader to make a connection between the mathematical abstraction of shear deformation and the behavior of real structures. Overlays are also useful for keying an area of an image to associated text.

The series of images below uses these techniques to illustrate the concept of bending moment.

Distribution

Conventional 35mm slides are usually only viewable for a few minutes in a lecture hall or classroom. The reproduction costs of color photographs preclude wide distribution. Digital images can be distributed over the world wide web, and are thus accessible to any computer in the world connected to the web. In teaching, this means that assignments can be based on viewing and analyzing the phenomena in images, and changes the role that photographs can play. The combination of image annotation and outside access makes it possible to create a much tighter linkage of structural theory and structural behavior.

Integration with text

As demonstrated in this document, digital images on the web can be integrated with supporting text to create a complete analysis and presentation of an idea. This medium makes it possible to effectively publish a slide talk, where the images serve as slides, the text serves as speech, and annotation serves as a laser pointer. The thumbnail image below is linked to a page containing an untouched EqIIS image, followed by a version of that image that has been cropped, scaled, sharpened, annotated, and accompanied by supporting text.

Slide talks are often the centerpiece of conference presentations, but they are never published in complete form because of the expense of color reproduction. Digital imaging and the web offer the possibility of enriching education and research by giving photographs a much more integrated role in the exchange of ideas among architects, engineers, and the host of other disciplines involved in seismic design.

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