Parallel Perspective

The existence of parallel perspective in Apophysis 3D hack is a gem of a treasure for those who enjoy stereoscopic images. It makes the process of setting up good views and getting stereo results that are consistently usable without eye-strain very easy. It is also the quality that makes it possible to create 3D Webscapes textures with Apophysis 3D hack.

Definition

Parallel Perspective is the special case where perspective lines DO NOT CONVERGE as distance from the viewpoint increases. It is different from normal perspective where perspective lines converge at a defined infinity point or points in the picture or off-picture but relating to the photo, drawing or illustration. Perspective lines themselves are usually not part of a picture but are an illustration to help us understand the effect of perspective. Another way of describing normal perspective is the observation that objects farther away appear smaller than the same objects nearby. By contrast in parallel perspective no matter how far away the object is it remains visibly the same size.

Parallel perspective can take a number of forms. Some location maps use a kind of parallel perspective. There might be a marker saying, “you are here,” and trails or roads lead to different areas within a region that is illustrated on the map. If it were a public park, little structure symbols might be used to show where bathrooms are available or camping sites, or picnic facilities exist. The symbols would be the same size for any location on the map. Trees and roads would be drawn to the same scale everywhere on the map.

Another kind of parallel perspective is used in what is termed “primitive art” which is a style typical of times in the past and the tendency of a number of modern artists to represent things in a simple style without attempting to portray a realistic perspective. Typically they show placid scenes of small towns or farms and houses. A painting might show several streets of a town with beautifully painted buildings on each street. The buildings pictured on a street at the back of the town would be essentially the same scale as buildings on the closest nearby street. Farm scenes might show cows and horses at the same size whether they are close to a road in the foreground or at the back of a distant fenced field.

Here are some images illustrating Parallel Perspective and comparing it to Normal Perspective. The first is Normal Perspective as you would experience in using a digital camera.

Normal Perspective and Stereo Camera

Normal Perspective lines spread out from the viewpoint. Nearby objects thus appear larger than farther ones. Normal every-day reality is experienced this way.

Parallel Perspective is uniquely different and fun to work with.

Parallel Perspective

It’s easy to see that in order to capture a larger Fractal, the virtual camera’s Render Size is increased enough to show as much of the Fractal as you might want. Distant portions of the fractal have the same size as a similar feature close to the virtual camera.

This next picture illustrates how a stereo image is captured in Apophysis.

Stereo Parallel Perspective

Apophysis Perspective

In the Adjust Panel <F5> of the 3D hack version of the program there is a control called “Perspective.” It’s purpose is to simulate the effect of normal perspective so that nearby objects seem larger than the same object farther away. The parameters for this setting can be adjusted to values that distort the image to an extreme degree. You could call that a “special effect” which generally you won’t want to use.

For most stereoscopic purposes the setting should be set to Perspective = 0 and left there. The following illustrations will show what this control does and why it is best left at 0 or only used in small amounts.

Stereoscopic images are generally pairs of very similar pictures. The precise differences between them are what make them stereoscopic. Their purpose is to provide image data to each eye that the brain can process into a recognition of depth placement in a volume of space rather than just placement on a flat surface. Yet the images themselves are flat because each eye has only a single perspective.

What changes are there between each eye’s perspective? If they are done correctly, there will be ONLY one definable change – a slight horizontal displacement of each image detail according to relative distance from the camera or viewpoint. Any changes other than strictly horizontal placement changes are errors and cause various degrees of eye stress as the mind attempts to connect the information in each picture in a recognizable way.

In order to render good stereo images with Apophysis the above information is important. When the Perspective setting is something other than 0, the result is that some image information will shift up or down during the attempt to define two stereo viewpoints.

Here’s an image designed by changing various parameters from those provided in a tutorial called Xaos Bubbles Tutorial, written by Nightmares06. Specifically, in Transform 1 the variation for Hexes=1 is changed to Hexes=0 and instead the Variation Flower=6 is used, along with the corresponding Variables, Petals=4 and Holes=1.125.

Correct Stereo Pair

If you wish to try and duplicate these results, note that instead of setting the Pitch to 60 as instructed in the tutorial, the Pitch here is set to 90 and the Final Transform is enabled and used to create post_rotate_x = 0.333. This change approximates the desired view-angle and specifically makes it possible to use the Yaw control to establish accurate stereo-camera viewpoints.

Adjust Panel Settings

Transform Editor FX enabled

The next picture has the value, Perspective=0.1. Note that the nearby flower is larger than it’s corresponding flower in the distance. This gives a nice perspective effect.

Perspective = 0.1

The image can be viewed in stereo because the discrepancies are minimal, but they do exist. Note the horizontal reference lines and the arrows which point out where image data has moved slightly up or down between the two side views.

As the Perspective value is increased or the Yaw is increased the errors tend to increase. The next illustration is not intended for stereo viewing as it uses a Yaw difference = 40 degree angle. This first picture has Perspective=0.1. Notice that the errors have increased especially for more distant background or closer foreground objects.

Perspective = 0.1, Extreme Yaw angle

The following final image has the same extreme Yaw difference angle=40 (+20 and -20), but this time there is NO perspective. The setting is Perspective=0. In this case, even though the change of angle is extreme the image details remain perfectly horizontal, they don’t move up or down at all. This illustrates what is happening in Apophysis and how to get excellent stereo results. It is possible to introduce small amounts of perspective for the effect as long as you keep it really small.

Extreme Yaw difference, no perspective