Contents

Repeated Dot Stereograms for Windows

This program allows you to create Single Image Repeated Dot Stereograms. Repeated Dot Stereograms create the illusion of depth by making the viewer focus to different distances.

How to

Create an RDS

See the RDS

More details

How do they work?

Source Image Format

Printing

Trouble Shooting

About the program

Known bugs

Contacting the Author

If you like this program, please take the time to encourage the author by sending him a postcard saying so.


Loading a source image
Source Image Format

This program accepts only Windows 3 bitmaps, and should accept all uncompressed Windows 3 bitmaps. If you cannot load a bitmap, see Trouble-Shooting.

Creating a RDS requires height information from the source picture. This is found from the brightness of each pixel: the red, green and blue components are averaged to give the resultant brightness. So, if your source picture is a grey-scale picture, you will have a better idea of how the RDS will turn out.

For smoother pictures, you may want to use 256-colour grey scale picture. As Paintbrush does not deal very well with these, you may prefer a shareware program like Pman.

24-bit pictures do load (albeit slowly on most machines) although it is wasteful to use these, as internally the program converts it to grey scale before any manipulation.


Generating an RDS

First, load a source image. See Loading for more details.

Choose Image| Settings to change any settings you want.

Next, choose Image|Generate, and wait for the RDS  to turn out.

Once it has finished, you can save it for printing.


Image Settings Dialog
 Image Settings Dialogue

Depth

Deepest and Highest control how far away from, and how close to you, the darkest and the lightest parts of the image will appear to be. The difference between Deepest and Highest is the number of steps of apparent height you will see. The actual values of the two variables will slightly affect the RDS at the edge of the image.

Period

This controls how much you have to defocus to see the RDS (See Seeing). For more details, see How do they work?

Static

Static means the RDS is generated from a random pattern of dots. You can control the brightness of a static image, by specifying a value between 0% and 100%, with 0 being black and 100 being white. . If you want to print out the RDS, you may experiment with this to find the best setting.

From file

This causes the regular repeating pattern of dots to be taken from a file, which you specify, rather than being generated randomly. The value you specify for Period determines how much of the bitmap is used; and if any more is needed, the bitmap is tiled. Choose Browse to select a file, or type its name in directly. Choose View to see the file you have chosen. Please note that, while coloured pictures can be loaded, the resulting colours in the image may be erratic.

Defaults

This option sets the values to their defaults. These are:

Deepest=0

Highest=16

Period=60

Brightness=50

You can change these defaults in the RDS.INI file, under the section heading [Defaults].


Seeing the RDS

At roughly arm's length from the computer screen, defocus past the screen. At a certain focus, some dots should become clearer; soon after, the entire picture becomes clear and you can see the three-dimensional image.

Some people prefer to focus in front of the screen. For them, the apparent heights are reversed.

If you can't see anything, all I can suggest is persistence.


Printing

This program does not provide any facility for printing: you will have to save the image, then load it into a paint program such as Paintbrush.

The resolution of a printer is far greater than that of the computer screen, and this requires changes. Firstly, increase the Period, so the distance behind the paper you need to focus is reasonable. You can work this out knowing the resolution of your screen and the printer: if the printer is 300dpi and your screen fits 100dpi, then increase Period by a factor of three.

This will allow a far greater range between Deepest and Highest, and will in turn make the printed RDS look smoother.

If you wish to use a file for your repeating dot pattern (see From file), it is suggested the file be monochrome, for more consistent output.


How do they work?

Hold up two fingers, and stare behind them until a third finger forms in the middle where the two seem to overlap.

Focussed on the two fingers	Focussed past, so they overlap in the middle

Now, move the fingers slightly apart, and change your focus so they again coincide in the middle. Move your fingers together, and focus closer to make the images coincide.

That is how Repeated Dot Stereograms work: but instead of fingers, random sequences of dots are used. If a sequence of, say 60 dots, is repeated, then you will be able to focus behind the screen to make adjacent sequences of dots superimpose. If in some place they are repeated slightly closer, you focus closer; if they are repeated with a separation greater than 60, then you focus further away.

So, to make the Repeated Dot Stereogram, fill in the leftmost 60 pixels on each line with a random sequence of dots. The 60 here, is the Period that can be set in the Settings dialogue box. Repeat this random pattern, so it covers the whole picture. Then, to make an area have an apparent height of one, squash the pixels in that area by, say deleting every 60th column.

Rather than use a random sequence of dots, you could use a regular pattern. You can achieve this with the From file: option in the Settings dialogue box.

Of course, this is an inefficient way to generate the RDS. If you want to look at the source code, see Contacting the Author.


Trouble-Shooting
Trouble Shooting

All I can see is a load of dots

See Seeing. Try taking of glasses, if you wear them. Beyond that, all I can suggest is to keep trying.

The RDS is inverted

Some people focus in front rather than behind.

Swap the values in Deepest and Highest, in the Settings dialogue, to make it appear the right way round.

I want the RDS to be smoother

Make sure you have set Deepest and Highest far enough apart.

My bitmap won't load

Firstly, the program will not load compressed bitmaps. Hardly any bitmaps are compressed, so this should not be any trouble. Seconly, it is intolerant as far as slightly corrupt bitmap files are concerned. There are also some older Windows 2 bitmaps which, although called bitmaps, will not load. Load them into Paintbrush or some other such program, and save. This should fix up the file.

The program crashes when I load/generate

Bitmaps take up lots of memory. Try closing other applications to free more memory.

There may be some problems with palette-switching: try closing other applications that use palettes, such as image-enhancing programs.

The dots aren't random

If the period is less than the difference between Deepest and Highest, the there will be peculiar effects in the image, making it quite non-random at certain heights. Typically there will be long streaks of black or white. Increase Period until it goes.

The colours in the image are messed up

When you have a coloured file for a pattern, it displays properly when you View it; but the RDS may have different colours. This is a program limitation: see Known bugs.


Known Bugs

Palette Switching

The palette often doesn't realise itself correctly when some other application changes the palette. This does not adversely affect the RDSs. If it troubles, you, switch to the main window, and the palette should display correctly.

Background not filled in for small windows

I don't know why this is. But it was Very Hard making the windows resize to entirely and only fit the image (except where this would be less than the minimum window width).

24-bit pictures

These take a very long time to load on most non 24-bit systems. Be patient; and use grey-scale pictures instead.

Coloured Pattern Files

These will be loaded and displayed correctly, when you choose View from the Settings dialogue box. But, when generating the RDS, the colours are reduced to the current system colours in a fairly arbitrary way.

Other bugs

If you encounter any other bugs, I would be very grateful if you could let me know, in order to improve the next version.


Contacting the Author

I can be reached by email at

djw1005@phx.cam.ac.uk

and by mail

Damon Wischik

Trinity College

Cambridge

CB2 1TQ

UK

During the holidays, email will be read infrequently.

If you want the source code (in Turbo Pascal, written under Borland Bascal for Windows 7), contact me at the above.

If you have any queries, suggestions or criticisms, please contact me also.

If you like this program, please take the time to send me a post card saying so. The encouragement will be much appreciated.


A Repeated Dot Stereogram (RDS) is an image which, when stared at, create the illusion of depth, through use of slightly differing periods of repetition.


The same effect can be achieved by having two images, which you stare at and cause to overlap; rather than just one image.


RDS
Repeated Dot Stereogram

A Repeated Dot Stereogram is an image which, when stared at, creates the illusion of depth. They are often called Random Dot Stereograms; however this program allows the creation of stereograms based on regular repeating patterns of dots.

For an explanation of how they work, ask How do they work?

For detail on how to see the illusion of depth, see Seeing the RDS.