Turnbull China Bikeride/Turnbull China Bikeride - Disc 1.iso/ARGONET/PD/GRAPHICS/IMAGE_1-.SPK/!Image/Docs/P20

Text File | 1995-05-08 | 8KB | 175 lines

3D Effects
==========


Single Image Random Dot Stereograms (or SIRDS)
----------------------------------------------


A SIRDS is a picture made up of what looks like random dots, but when looked
at correctly a three dimensional picture can be seen. More details, plus
hints on actually looking at these are given at the end of this section. But
to start with how to produce them using Image.


The SIRDS Control Window
------------------------

This control window is available from the main Control Panel (the icon marked
'3D'). this window contains a number of icons and options, many of which can
be ignored (but they allow greater control of the conversion process).

To produce a SIRDS Image needs a start picture which needs to be quite large
(of the order 300x300 to 600x600 pixels). In order to work out the depths of
the various parts of the picture the rule followed is that dark objects are
in the far distance, light objects in the near distance, thus by careful use
of various intensities you can create many different layers.

Basically once you have a suitable picture you can just select the 'Create'
icon and Image will produce you a SIRDS based on that picture.

Now what about all the options. First the three options on the top left of
the window, marked 'B&W', 'Grey', 'Colour' and 'Picture'. These select the
output SIRDS as being either a plain black and white SIRDS, one using 8 grey
values, and a colour one (using the eight desktop colours). Black and White
SIRDS are very fairly standard; grey scale ones can be slightly easier to
see; the colour ones just add a bit of colour. The 'Picture' option is
detailed below.

Please note that you should not use dithering on SIRDS output sprites as this
will destroy the illusion.

Down the right hand side of the options are three settings which contain
values, none of which need to be very accurate, but just approximately
correct. The first is the number of dots per inch the output is to be treated
as. Normally a value around 90 should be used for displaying on screen.

The second value is the separation of your eyes (in inches); so unless you
have very odd eyes you should not need to alter this value.

The final value is a fraction (you specify the denominator). This defines the
field depth to use when judging how far different objects are. Altering this
value will cause the near objects to move nearer or further away (increasing
or decreasing the effect). Basically by increasing the value in the icon (ie.
making the fraction smaller) will decrease the field depth, reducing the
value will increase the depth. The default value is 30, giving a field
depth of 10/30, or 1/3.

There are two options towards the bottom left. The first, Hidden surface
removal, (when selected) produces more accurate results (but is slower). The
second option, Focus Dots, (when selected) causes the output to have two dots
placed at the bottom of the picture. These dots can be helpful to people
who have trouble seeing the illusion (see below).



An example
----------

As a small example, first create a picture of about 600x400 pixels and, using
the paint operations, make the background black and place a medium grey
circle in the centre of the picture (make the circle about three quarters the
height of the picture). Then draw a white circle on top of that, making it
about half the height of the picture.

Then (using 'Over') merge that into the main picture and close the 'Paint'
operation window ('Abort' or 'Close').

Now bring up the 'SIRDS' window and select the 'Focus Dots' option and set
the type selector to either 'B&W' or 'Grey' (Grey is probably better).

Now select 'Create' and wait for the SIRDS to be created.



How to view a SIRDS
-------------------

One of the most difficult parts of SIRDS is actually seeing them. It is
something that needs to be practiced, and it can take quite a while before
you see your first one properly (sometimes as long as a quarter of an hour) -
so make sure you have plenty of time.

Please note: Some people will never be able to see SIRDS, those particularly
affected are those with one dominant eye, or those with a lazy eye. Short
sighted people tend to find seeing them easier than other people.

The trick to seeing them is to decouple your eyes' convergence and focusing -
something that you won't normally do.

To get started you should try using the 'Focus Dots', these are two red
squares at the bottom of the SIRDS (if you have set the 'Focus Dots' option
when creating the SIRS).

Place your head about 8 inches from the screen (the exact distance will vary
from person to person, and upon the settings used, and you monitor size) with
your eyes in line with the two red dots.

Now you need to try to stare through the screen, as if trying to focus on
something behind it. You should now see 4 red dots instead of two. What you
now need to try and do is (by varying you focus, or moving your head back and
forth) get the two middle dots to merge together - thus you see three dots.

Once you have managed to get three dots in vision you are correctly focused
to see the SIRDS. Fix your vision on the centre dot and then carefully allow
you gaze to wander around the whole picture (keeping your eyes focused
through the screen). You should now see a 3D image of (in the above example
picture) two circles one in from of the other, and a back plane in the
distance. Once you start seeing it, you will find your eyes will lock onto it
and you will be able to examine the picture in more detail, which will also
increase the 3D effect.


'Picture' SIRDS
---------------

The three options detailed so far use a random colours when producing the
output picture. Another option is to use a picture, repeated (tiled) in the
output. This produces results more like those you can buy as posters.

To use a picture in the output you need to place the desired picture for the
SIRDS algorithm to use in the 2nd input bank and select the 'Picture' option
on the SIRDS window.

Below the 'Picture' icon is a small square icon with a value beside it
(eg. 113x199). This gives the maximum size the picture (to be tiled) can be.
The first value (width) is fixed by the settings for the SIRDS and details
the maximum width the tile can be so that the whole tile width is used in the
output picture. The second value (height) gives the maximum height which can
be used if the tile is the maximum width given. If you make adjustments to
the settings then you will beed to press the small square icon to update the
maximum tile size values.



Drop Shadow Effect
-------------------

Image can automatically produce a drop shadow using the 'Drop Shadow'
options in the 3D Effects window.

A drop shadow gives the impression that an area of a picture is raised above
the other areas in the picture be creating a 'shadow' by darkening areas
offset from the area which are to appear raised.

In order to create a drop shadow you must first indicate which areas of the
picture are to appear raised; this is done by masking out these areas using
the many masking facilities provided by Image.

Next all you need to do is specify a few parameters about the drop shadow,
these are a set of x and y offsets for the drop shadow and the darkening
factor.

The offsets define how far the shadow appears from the original raised area,
the larger the number the greater the raised effect.

Positive values make the shadow appear to below and to the right of the
raised area.

The darkening value defines how much Image should darken the areas of the
picture where the shadow lies. The brightening value should lie between -255
and 255, a negative darkening factor will brighten the area in the shadow.