Richard Baldwin is a Professor of Computer Information
Technology at Austin Community College in Austin, Texas, USA.
Prof Baldwin first became involved in the issues confronting blind
students when a blind-from-birth student named Amanda Lacy enrolled in an
object-oriented programming course that he taught. Ms. Lacy successfully
completed that course and two others that he taught. Knowing that she was a
very good student, he became concerned upon learning that she was having
difficulty in a physics course. Being an engineer by training, he volunteered
to tutor her in the physics course. This led to the two of them spending about
four hours per week in tutoring sessions for the past couple of years.
Prof. Baldwin quickly learned that neither the physics lectures
nor the physics textbook were accessible to Ms. Lacy. She had stopped attending
lectures because she was unable to follow along. The electronic copy of the
textbook that she had been provided contained hundreds of equations and
pictures that were incompatible with her assistive tools: a screen reader and a
Braille pad.
Prof. Baldwin began by authoring an online physics tutorial
titled “Accessible Physics Concepts for Blind Students” (available here) to help Ms. Lacy through the first semester physics course. Although it took
more than one semester for her to complete the course, she did complete it and
made an A in the course.
While authoring the online physics tutorial, Prof. Baldwin
came to realize that unlike sighted students, blind students were unable to
draw and submit graphical homework assignments, such as vector diagrams with
any accuracy. Although there are several outstanding free drawing programs
available on the web, all or at least most of them require the user to
manipulate a mouse. Therefore, they are not accessible to blind students. As a
result, Prof. Baldwin wrote a drawing program named SVGDraw01 that is fully
accessible for blind students. The theme for this program is “if you can
imagine it, you can draw it.” The program is freely available for downloading here.
Later, Prof. Baldwin decided to tackle the inaccessible
pictures and diagrams in textbooks. One technique that blind students can use
to understand the content of diagrams and pictures is to emboss them using any
of several available embossing techniques. Basically, embossing an image means
to create a tactile document containing raised lines or raised dots that
describe the salient features of the image.
Originally, Prof. Baldwin hoped to make it possible for
blind students to emboss their own textbook images. So far, that is still a
dream for several reasons. The most common format of electronic textbook is the
Adobe pdf format. Without the purchase of expensive software (and probably not
even then), it is impossible for a blind student to successfully extract most
of the images in a pdf file intact. While there are numerous programs available
that claim to extract the images from pdf files, in most cases each image ends
up in several different files that must be reassembled for embossing.
After coming to that realization, Prof. Baldwin decided to
direct his attention to the many technical issues that make it very difficult
for even a sighted person to convert a typical bitmap file into an embossed
image that is meaningful to a blind student.
There are about 16-million good reasons why the embossed
version of a full-color bitmap image often fails to produce satisfactory
tactile results. Begin with the fact that the embossing process often discards
the information content from more than 16-million colors ending up with what is
effectively black and white, or possibly black and white with two or three
shades of gray in between, depending on the embossing method.
Follow the loss of color information with the fact that,
unless the original image is very small, the spatial sampling is probably
reduced by a factor of 5 to 10 in the embossed image with little or no
consideration being given to frequency aliasing that occurs in a brute-force
spatial re-sampling process.
The bottom line is that it is very difficult to emboss
full-color bitmap images and end up with high-quality tactile images.
Different embossing methods produce different physical
outputs. Many of the older Braille printers have a graphics mode that allows
pictures to be displayed by raising a subset of individual Braille dots to a
standard height. The dot separation on those printers ranges from ten dots per
inch to perhaps 17 dots per inch. Compare this with the typical 96 dots per
inch of an image on a computer monitor and you will understand the issues
regarding spatial sampling mentioned above. When the image is re-sampled down
to a level that is consistent with the number of dots in an embossed image,
much of the detail simply disappears.
Newer Braille printers have dot resolutions of up to 25 dots
per inch, which is still very low in comparison with onscreen images. Some of
them can also raise dots to variable heights to simulate gray scale imaging.
Although there is no published information as to how many “gray levels” can be
understood by an experienced blind user of an embosser with variable dot
height. Prof. Baldwin estimates that such a user can probably recognize black,
white, and perhaps three gray levels in between.
Typical embossing techniques either convert the 16 million
colors in a bitmap image to black and white through the application of a single
intensity threshold, or convert the 16 million colors to black, white, and
several shades of gray through the application of several intensity thresholds.
The result is that many colored pixels that are clearly distinguishable in the
original image become indistinguishable in a four or five-level gray scale
version of the image. Detail that depends on the recognition of different
colors simply disappears. Therefore, many of the salient features of the image
are often lost in the embossing process.
Prof. Baldwin has developed a mathematical image processing
algorithm which, in many cases, preserves much more detail than the typical
intensity-based gray scale approach. This algorithm converts the original image
to either black and white or black and white plus three levels of gray, based
not on absolute colors, but rather based on changes in color. The result is
that images processed using this algorithm tend to have black outlines that
define the salient features of the original image. In many cases, this produces
more meaningful embossed images than the typical approach based on the direct
conversion of color intensity to gray scale.
Prof. Baldwin’s solution to the spatial sampling issue is to
make it possible in his programs to subdivide an enhanced image into panels,
which can be individually embossed and then assembled into a poster-size
tactile image. While not an ideal solution, short of developing an embossing
method with an improved dot resolution, that is the best he has to offer.
Prof. Baldwin and Ms. Lacy have packaged the image
enhancement algorithm in a free computer program designed specifically for use
with embossers that support a single dot height and accept Duxbury graphics
files in the .sig format as input. This program is named JpgToSig-A-01. It
accepts any of several different bitmap image files as input and writes the
enhanced version of the image into an output sig file. While it is possible for
blind students to use the program, it is primarily targeted for use by teachers
and others who assist blind students.
Prof. Baldwin has also packaged the algorithm in a free
computer program named ShapeExtractor02 that is designed for use with any
embossing method that can accept jpeg image files as input. This program
accepts any of several different bitmap image files as input and writes the
enhanced version of the image into an output jpeg file. Both of these programs
can also be freely downloaded here along with the program named SvgDraw01. Note that all three of these programs
require the Windows operating system.
These programs can be used with bitmap images from any
source. However, in the world of education for blind students, the images that
need to be embossed are often contained in electronic pdf versions of course
textbooks. Prof. Baldwin uses the following procedure to assist Ms. Lacy in
embossing images from her physics textbook.
- Open the pdf file in the free version of Adobe Acrobat and locate the image of interest.
- Use the zoom capability of Acrobat to make the image as large as possible while still fitting on the screen.
- Hold down the shift key and press the Print Screen key. This saves the current screen image on the clipboard.
- Open any of many available image editing programs such as the program named Lview Pro.
- Paste the clipboard into the image editor.
- Crop the image out of the surrounding material retaining only the material necessary to contain the image.
- Save the cropped image.
- Open either JpgToSig-A-01 or ShapeExtractor02 and follow the usage instructions to convert the image to the desired black and white or black, white, and gray format.
- Save the enhanced image in an output file and emboss it using the embossing method of choice.
Ms. Lacy is now enrolled in her second physics course and
plans to complete several more.
- As told by Prof Baldwin
