gbSIRTS - Single Image Random Text Stereograms
Most users are familiar with stereograms, the random dot variety and those
which use tiled images in the background. But stereograms can also be made
using text - using characters where other types of stereograms use pixels.
gbSIRTS quickly and easily generates text stereograms - called Single Image Random Text Stereogram (SIRTS). gbSIRTS also has a "mosaic" mode which substitutes a small, colorful bitmap for each character.
See my Stereogram Information Center for background information on stereograms and my gbStereogram freeware program which supports the other types of stereograms.
gbSIRTS key features include:
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 Overview
Operation
Toolbar
Paint Mode
Menu
Change History
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Download (ver 2.5, 1.0M)
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Mosaic Stereogram (3D image of 2 overlapping squares)
 Gradient Background |
 Colored Text |
Manual Paint Mode | 
Imported Depth Mask | 
Text Depth Mask |
I've released a freeware program called gbStereogram which can generate both types of stereograms.
This page, however, describes a second freeware program call gbSIRTS which generates a lesser-known type of stereogram - one which uses text as a background. Stereograms with text backgrounds are called single image random text stereograms (SIRTS).
The Bad News
Text stereograms are generally not the most popular type of stereogram because they suffer
from a more pronounced layering effect, whereby the 3D objects to appear to made of layers
with pronounced separation. This also limits a text sterograms to no more than about
10 total layers before the brain has trouble visualizing the 3D image.
The layering affect also happens in random dot stereograms, but because the dots are small, graphical techniques can be applied which significantly smooth out the layering effect. The smoothing is particularly effective on sterograms which use image backgrounds.
Unfortunately, there are no layer smoothing techniques for text stereograms so while they are particularly convenient and fast to create using computers, text stereograms do not provde the colorful eye-candy of the other types of sterograms.
I've considered generating a custom font which might be used to smooth a text stereogram. The idea would be for the font to contain less white space and the font characters would not be applied randomly, but rather placed at level transition points to help smooth out the final image. I'll be looking into this approach and will add the results to gbSIRTS if it works out!
The Good News
The eye-candy problem aside, text stereograms are every bit as exciting to view. I'm addicted
to 3D imagery in general and even the simplicity of text stereograms is fascinating. As a programmer
text stereograms are particuarly exciting becausing text manipulation of a screen full of data
is much faster than manipulation a screen full of pixels. gbSIRTS can generate text stereogram
images, including animations, far faster than full size images.
There are other tricks which help close the gap. Most importantly, gbSIRTS uses a computer font which supports fonts down to size 6 - not dots, but small enough for most folks eyes to lose the distinction of individual characters.
The other good news about gbSIRTS is that while it contains built-in Paint functions to generate custom depth masks, it can also use the depth masks that are used to generate random dot and image background stereograms. This means you can search the Internet for find hundreds of existing mask which can be used in gbSIRTS.
When started the first time gbSIRTS automatically generates a text stereogram using one of the built-in depth masks. Pressing the "Create Stereogram" button will re-generate a new stereogram using the current depth mask. Pressing the "Shimmer" button will repeatedly create a steregraom using the current depth mask.
Use the "Shape" button to change to a new built-in depth mask, or to change to Paint Mode, to create a customer depth mask.
All of the features of gbSIRTS are accessed from the toolbar or from the Depth Mask frame which is displayed only when gbSIRTS is in Paint Mode
Depth Masks
gbSIRTS can import a depth mask from an existing file. It also allows the user to manually
create a depth mask using simple built-in paint tools. The paint tools provide the ability
to create depth masks from the following elements: square, circle, line, and text.
Built-In Depth Masks
In addition to allowing the creation of a custom depth mask, gbSIRTS can automatically
create depth masks of three types - squares, circles, and bars. When a built-in
shape is chosen from the toolbar, gbSIRTS automatically creates a depth mask with
the selected shapes and will display it when the "Create Stereogram" or "Shimmer" commands
are selected on the toolbar.
Note: In paint mode the custom mask is displayed, which the user can modify. Depth masks for the built-in shapes are not displayed in paint mode.
Layers
In paint mode, gbSIRTS can generate a depth mask with up to 8 layers. The layer is
determined by the shade of gray used to make the depth mask image and gbSIRTS allows
the selection of eight different shades.
Eight was chosen because it represents the maximum number of layers most users can easily visualize within a text stereogram.
When a depth mask is imported it may contain many more shades of gray than gbSIRTS provides. By default, all shades of gray that do not match one of the 8 default layers are placed in a 9th layer.
However, the "Use Custom Levels" context menu selection can be used to have gbSIRTS provide a finer control of the layers displayed in the 3D image. The context menu "Custom Levels" allows the user to attempt to display up to 40 total layers. In most cases, anything display with more than 10-12 layers is very difficult to see, but when visible the greater number of layers more accurately represents the imported depth mask.
Shimmer
Shimmer refers to repeatedly creating/displaying a new stereogram using the same depth mask. Shimmering
is a means of helping view the 3D content. Even though each new stereogram has a different
set of random characters, the 3D image remains constant and the act of repeatedly displaying
the image within a changing background helps the brain focus on the hidden 3D image.
Animation
The animation capability of gbSIRTS can only be applied to the built-in depth masks. When
both shimmering and animation are activated each successive stereogram will display the
3D images in a new position.
Pattern Width
The algorithm used by gbSIRTS calls for a specified number of characters to be used as
the repeating stereogram background pattern. No one pattern
width is best for all depth masks, so gbSIRTS allows the user to adjust the pattern width
to optimize viewing of the stereograms.
Background Text
Even though a SIRTS is defined as a single image random text stereogram, the background
text does not actually have to be random. A fixed background text can also be used. As
part of creating the stereogram the background text is manipulated but remains easily
distinguised in the resulting stereogram.
Colored Text
By default, gbSIRTS uses black text because when all of the characters are the same color
the brain can readily detect level changes. By randomly colorizing the text the brain has
more difficulty in detecting the 3D image. I added the colored text option just to be able
to see experiment on the effect. You can still see the 3D images, but they are definitely
more difficult to keep visualized.
Font and Character Set
The output font of gbSIRTS is set to 'Courier New', a fixed width font because fixed width
fonts are most conducive to creating the 3D image within the stereogram. gbSIRTS supports
selecting a new font, but using a variable width font will give poor viewing results.
gbSIRTS also allows the selection of 3 sets of characters within the font - all capital letters, all lower case letters, and all symbols (ASCII codes 33-122). The use of specific character sets changes the amount of white space, which impacts the ease with which the 3D image can be viewed. However, viewing is generally not greatly different with any of the three options, although some users may be more affected than others.
Algorithms
There are four separate algorithms available in gbSIRTS.
The first three are based on an algorithm which creates a pattern of text, then applies modified versions of that pattern repeatedly from left to right in the image. Two of the three algorithms are allowed to reuse characters from the pattern, while the third prevents the reuse of characters.
The fourth algorithm (which does not work very well as of release 2.0 - I'm working on it!) applies a totally different algorithm which positions text characters on the basis of the separation they would have on an image plane between your eyes and the 3D object being viewed.
My Stereogram Information Center provides more information on these algorithms.
Mosaic Display
Normally, gbSIRTS displays a text output but when the mosaic display option is selected,
each character is replaced by a small, built-in bitmap. The result is a much more colorful
display. Also, the 3D content is generally much easier to see.
The display of a mosaic takes about 0.3 seconds, so while the shimmering effect can be applied it will not repeat as quickly as plain text.
Save Images
The Save option of gbSIRTS saves the depth mask, or stereogram - whichever is visible at the
time Save is pressed - to a specific file name in the installation folder of gbSIRTS.
The text stereogram is saved to 'gbsirts_stereogram.bmp'. The depth mask is saved to
'gbsirts_depth.bmp'. gbSIRTS does not support saving the images to specific filenames/locations.
Files are saved as .bmp only.
Also, when gbSIRTS is closed, the current custom depth mask is automatically saved to the file 'gbsirts_depth.bmp'. This same file is automatically read into gbSIRTS when it is started.
gbSIRTS can also save the stereogram image, stereogram text, or paint image to the clipboard.
When in SIRTS mode, the following context sensitive menu options are provided:
When in Paint mode, the following context sensitive menu options are provided:
