Introduction to 3D Imaging

Size: px

Start display at page:

Download "Introduction to 3D Imaging"

Georgia Ray
8 years ago
Views:

1 Chapter 5 Introduction to 3D Imaging 5.1 3D Basics We all remember pairs of cardboard glasses with blue and red plastic lenses used to watch a horror movie. This is what most people still think of when confronted with the words 3D. What they tend not to know is that 3D imaging is much, much more than this. In fact, 3D imaging is a growing multi-million dollar industry; recently Harry Potter and U2 films have been produced in 3D. However, the industry is a tight-knit community with it s secrets well hidden. 3D imaging is nothing new. In fact it has been around since humans first developed two eyes. The reason for having two eyes may not be immediately obvious. In most cases, including that of the average Joe, while giving a better range of view, two eyes are placed next to each other to produce stereo vision. Each eye picks up a slightly different view of the same scene (see Fig. 5.1) and it is these differing views that allow our brains to translate depth information to us, and to give substance to our vision (the word stereo comes from the Greek word stereos, meaning solid ). So, what do we have to do to reproduce 3D images? We have to give each eye a different view of the same scene. Anaglyph images (those bluered images only viewable with the blue and red glasses) attempt to do this by mixing the two images using different colours, and then filtering out a different image for each eye. While effective in producing an impression of depth, it requires the wearing of the coloured glasses. This has two problems...it affects the colouring of the image, and you need to wear special glasses to see view them. While anaglyph images give a measure of depth, they only allow for 2 view points. Holograms, on the other hand, allow for multiple viewpoints and so a constant 3D movement around the subject is produced. Holograms are created using a complicated system of a split laser beam and photographic substrates. Various different techniques are available but all rely on the same underlying theory. While colour holograms are possible, they are extremely expensive and complicated and the subject matter is very restricted. Most people will mostly know holograms as the more common green-orange-blue combination images and, as with anaglyph images, colour information is lost in their production. Also, to produce a hologram a complicated setup of lasers and mirrors 12

In fact, 3D imaging is a growing multi-million dollar industry; recently Harry Potter and U2 films have been produced in 3D.

2 (a) Plan view of the scene. (b) Left eye view. (c) Right eye view. Figure 5.1: Your eyes and brain produce a 3D image by taking in 2 different views of a single scene. is needed, and therefore the equipment could neither claim to be affordable or portable. So anaglyph images give depth but need to be viewed with glasses and much of the colour information can be lost. Holograms give movement around the subject as well as depth, but the process is expensive, complex and usually confined to a laboratory environment. So what we really want is a way to produce an image that you can view in normal light, in it s natural colours, which gives both depth and movement around the subject, doesn t require you to use any special goggles or glasses to view it, doesn t require you to be confined to a lab and doesn t require you to re-mortgage your house to create. Surely that s not too much too ask!?! Well, it may come as a surprise to you that there is a technology that covers all these bases, called Lenticular Photography. A lenticular image is comprised of a number of 2D images moulded together into a single 2D interlaced image. When a lenticular screen (usually a plastic laminate) is placed onto the image, the viewer sees a different view of the subject dependent on the angle the 13

So anaglyph images give depth but need to be viewed with glasses and much of the colour information can be lost.

3 lenticular image is viewed from. And so when you view the image with your two eyes, each eye picks up a different view of the subject and this gives the image depth and substance. There is no trickery to this effect...it is exactly the same effect as if you were viewing the actual object. This means that lenticular images have a natural, Real 3D feel to them, as if you could just reach out and interact with them. This is what makes lenticular imaging special. Other advantages are that the lenticular image required no special lighting conditions to be viewed and the colours in the image are not affected by the process. Also, the effect is partly produced by the lenticular screen, and when this has been laminated to the front of the image no special glasses or any other type of viewing medium is needed. Lenticular image production is also relatively cheap, even for one-off productions, which is not true for holograms. This all means that lenticular photography is the most accessible and effective form of 3D imaging...in a league of it s own with regard to impact on the viewer. The obvious question to ask is why don t we see lenticular images everywhere already. Up to now, the process of creating a lenticular image had the same drawbacks as holography; the equipment is large, sensitive to vibrations (it is often kept underground, weighed down by cement and floating on a bed of air!), needed a large power source and is very complicated. Needless to say then that it is also very expensive, which means it is only accessible to large advertising companies. Also, lenticular images are generally very high resolution images, which meant sending the images to a lithographic printer to be printed. Again this added cost to the process. Cheaper methods were developed in the 70 s and 80 s including cameras equipped with multiple lenses that split a 35mm frame into a number a smaller frames (usually 2), each a slightly different angle of view of the subject. Because of the limitation on the number of frames and the cheap plastic lens used, these images were rarely blown up to a large size and had little feeling of depth to them. Of course, you also had to wait to get your film developed before you could see if the shot worked. 5.2 Lenticular Imaging When viewing a 3D scene your left eye and right eye each capture a different angle of the subject (as shown in Fig. 5.1). So to reproduce 3D effects, a different image must be delivered to each eye. To achieve this, we utilise a technology known as Lenticular Imaging. This process uses a plastic lenticular screen, consisting of rows of curved lenses. As light enters a curved lens, it is diffracted through an angle. It is this action which is used to deliver different images to each eye. Fig. 5.2 shows the effect of looking through a lenticular screen. Images of the scene from different angles are placed in strips behind the lenticular screen (the process of generating these strips is known as interlacing and is carried out by the Mitton3D Interlace Software which accompanies the LR1). The effect of the curved lens means that when viewed from different angles, a different frame is visible behind the lens. And so each of your eyes picks up a different frame behind the image, and a different angle of view of the photographed scene, just as with natural vision. While two images is all that is required for the 3D 14

This means that lenticular images have a natural, Real 3D feel to them, as if you could just reach out and interact with them. This is what makes lenticular imaging special.

4 Figure 5.2: Lenticular screen allows different images to be displayed to each eye. The left eye sees Frame L, the right eye sees Frame R effect, further images are required to make the image appear smooth and to give the sense of looking around the subject. With these processes we can produce stunning True 3D images for any scene or object you can imagine. The Mitton LR1 is your key to 3D. Tip: If the order of the images is reversed, you achieve an effect known as Pseudoscopy. This is a reversal of natural depth perception, where, for instance, a box on a floor would be perceived as a box-shaped recess in the floor. Some interesting effects can be achieved using this method. The order of the frames can easily be reversed in the Mitton3D Interlace Software (See page 32). 5.3 Lenticular Lens Lenticular screen is made in various different lpi (lenses per inch), of which the most common are 40 and 60 lpi. These screens are effective because they have useful viewing distances (40 lpi works well from about 4 feet to 15 feet) and give a good sense of depth. The images are also well suited to current printer resolution capabilities and the file size of the images remains small enough to easily transfer between computers. These lenses both have a viewing angle (the angle in front of the image in which the 3D effect can be experienced) of approximately 25 degrees. The thickness of the lenses also 15

With these processes we can produce stunning True 3D images for any scene or object you can imagine. The Mitton LR1 is your key to 3D.

5 changes with the lpi; 40 lpi lens being approximately 80 mm in thickness and 60 lpi approximately 50 mm. At the extremes of available resolutions are 10 and 100 lpi. 10 lpi lens is used for very large billboard projects. With this lens viewing distances are very long and viewing angles are up to 50 degrees. This lens is also used for large projects as though the physical dimensions of the image are very large, the resolution can be kept low and therefore file sizes are kept low enough for standard computers to process. 100 lpi lenses are used for small, hand held lenticulars. These lenses produce very clear images, but with less of a perception of depth than other lenses. File sizes can also be huge for these images because of the extremely high image resolution required. Expensive, specialist printers are also required to print to this resolution. 16

This lens is also used for large projects as though the physical dimensions of the image are very large, the resolution can be kept low and therefore file sizes are kept low enough for standard

WHO CARES ABOUT RESOLUTION?

WHO CARES ABOUT RESOLUTION? At Poli we certainly do not care about resolution as a concept! However we do care deeply about resolution when used as a measure of quality. Resolution is a very dry and technical