Tag Archive: Persistence of Vision


Stop Motion Photography

Stop-Motion Photography

Stop-motion (also referred to as stop-action) photography was one of the first “special effects” techniques ever invented. It is a form of animation and allows otherwise lifeless objects to move and change. Much of the early use of stop-motion in the cinema was to make models of dinosaurs apparently gallop by themselves. Stop-motion continues to be used today in commercials (like the singing California Raisins) and children’s fantasies like Rudolf the Red Nosed Reindeer.

Movies and television work by displaying to the viewer a series of pictures. Each picture is identical except for the action that is changing in the scene. If the images are flashed up fast enough around ten a second the brain will see them as a single picture with moving elements. This effect is known as persistence of vision. Motion pictures are usually projected at 24 frames a second and video at 30 frames a second (although this comes in the form of two interlaced half frames every 60th of a second).

kong sex violenceMotion picture cameras record by exposing frames (24 a second) one after another so that movement, like a person walking down a street, is captured. If the camera is pointed at an inanimate object, like a vase on a table, and the frames are exposed one at a time so that in between shots the vase can be moved a fraction of an inch, then film when projected back at normal speed, will show the vase apparently moving by itself. The same can be done with elaborate jointed models on miniature sets to give the impression that the models are alive and walking around by themselves. In addition to models, clay and drawings are often used with this technique. When drawings are used it is generally referred to as cartoon animation.

One of the earliest shorts produced using stop-motion was The Missing Link. Willis O’Brien, a pioneer of stop-motion, completed this comedy in 1916. O’Brien went on to later do the stop-motion for The Lost World in 1925. His most well-known work was King Kong (1933). O’Brien’s work inspired a new generation of stop-motion artists including Ray Harryhausen (left). Harryhausen worked on dozens of films animating everything from dinosaurs and dragons to an army of sword-fighting human skeletons for the film Jason and the Argonauts. Harryhausen was the premier stop-motion animator of his day, and his name on the film was every bit as important a draw as the lead actors.

Stop-motion photography requires long hours of hard work to produce even a few seconds of film. A single error can cause many days worth of material to be lost. For this reason, the camera, set and models are carefully clamped down to eliminate unexpected movement between shooting each frame. In King Kong, much of the miniature foliage was actually made out of metal to keep it rock steady.

Kingkong02The Kong crew ran into trouble while filming one sequence when a live primrose plant, used in a jungle scene, went into bloom one day during filming. Nobody noticed this until the film was developed and viewed. In the background appeared a perfect time-lapse sequence of a white flower opening. The entire scene, a day’s work, had to be re-shot.

The Kong crew also ran into trouble with the rabbit fur that covered the eighteen-inch-high Kong model used in the production. As the animators adjusted the Kong model in between shooting frames, their hands disturbed the hair. The producers of the film were appalled when these showed up as obvious ripples on the head and shoulders of Kong during an important screening for studio executives. Fortunately one of the VIPs cried out in excitement, “Hey, Kong is mad! Look at him bristle!”

Since producing stop-motion sequences were so labor intensive and expensive, animators often had to find unique ways to cut costs during production. Ray Harryhausen, while filming It Came From Beneath the Sea (right), the saga of a giant irradiated octopus that ate San Fransico, was forced to reduce the number of arms on the octopus model from eight to six to help keep the picture on budget. Harryhausen also came up with a split-screen process that allowed the stop motion models to be placed in scenes with real buildings and people. This lowered the costs of producion and made the action seem more realistic. Harryhausen called this process Dynamation.

Despite the careful work of artists, like Harryhausen, stop-motion photography had some inherent limitations. One of the most important is its inability to accurately represent quick motion. When a man runs by a camera during traditional filming, his movement is quick enough to cause a blur on each frame. An animated dinosaur running by the camera will not blur because each frame is a photograph of a still model. Our eyes can perceive the difference and stop-motion dinosaurs which are running will always seem to move in a staccato fashion. George Lucas tried to solve this in Return of the Jedi, through a method he called go-motion. It involved filming a puppet at high speed. Because the action was not stopped a proper blur was recorded, but since the monster puppet was being photographed in real-time, it was limited in the actions it could perform.

jurassic-park-t-rexComputer animation has now replaced stop-motion in almost every application where the film maker is trying to create a realistic effect. In computer animation the model is constructed within the memory of the computer. This allows the model to be more versatile and detailed. The computer can also blur frames to simulate movement and it is easy to go back and make changes in the middle of a scene, something that was impossible with the older stop-motion method. Computer animation is so effective that in the film Jurassic Park it is impossible to tell the full-sized dinosaur puppets from the computer-generated animals.

Stop-motion isn’t completely gone, however. Sometimes film-makers prefer it because of the special style it gives the picture.

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Persistence of Vision

Persistence of vision

persistence-vision-1Before we get on to the nitty-gritty of animation timing it might be useful to briefly cover the principle that underpins film and animation, and to understand how the illusion of movement is achieved where none is actually present. This marvellous phenomenon is known as the persistence of vision and it is through this that we experience moving images made up of individual frames on a film strip.The secret of this illusion is to be found in the remarkable capability of a part of the human eye, the retina, of momentarily retaining any image it receives. Imagine, if you will, a light being shown into the eye only briefly and appearing on the retina as a bright spot. This bright image would appear to remain for a brief period even after the light had been turned off. It’s this slight period of retention or delay that allows for separate sequential images, if seen in quick succession, to appear as a moving image, and it’s upon this principle that film and video projection works. Although this phenomenon had been observed in ancient times, it wasn’t until the systematic experiments in 1765 by the Frenchman, Chevalier Darcy  that it was established that this retention period was approximately one-tenth of a second. The early optical devices that were developed and began to appear in the first half of the nineteenth century clearly demonstrated this effect. What started out as serious scientific investigation soon found a practical application for entertainment through the use of such devices as the thaumatrope, the zoetrope, Joseph Plateau’s phenakistoscope and Emile Reynaud’s praxinoscope. Variations of these quickly began to appear as popular parlour toys in the homes of the upper classes throughout Europe.

 

Frames per second
All animators, irrespective of what discipline they work in (2D classical animation, stop-frame animation or computer animation)24 Frames and despite what work they undertake (commercial, studio-based or experimental animation), all use the same basic raw material to create their work – time. They use this in much the same way as a painter uses paint or a sculptor uses stone, and while this raw material shapes and defines their work, what they choose to do with it is another matter. The use of time varies from animator to animator, just as paint does with a painter, and it’s this varied approach and use of time that helps make the variations in stylistic execution of animation, be it funny or tragic, naturalistic, cartoon or abstract. The basic unit of time we deal with as animators and film-makers is determined by the recording and projection rate of the individual film frame or video image. This rate is commonly known as frames per second (fps).

While this playback or projection rates have varied since the development of cinematography, the standard recording and playback rate for film and video usually equates to:

● Film – 24 frames equals 1 second.

● Video – 25 frames equals 1 second (PAL).

● Video – 30 frames equals 1 second (NTSC).

These figures become critical in achieving the illusion of motion. As we have already established, the persistence of vision retention rate is around one-tenth of a second – much longer than the fps projection rates for film or video. If the projection rate was below that of the retention rate on the retina, the sequence of images would appear jerky and as individual images, and the illusion of movement would be lost. Because animators determine the speed of action of all they animate by creating animation timing, rather than recording movement as in live action, it is possible to achieve all of the variable animation timings they could desire. Working within these normal fps rates does not constrain the creative potential for animation, other than on purely technical issues, and is generally not noticeable to the eye. By comparison, live action film-making depends upon ‘recorded’ time as opposed to ‘constructed’ time. The timing of action is recorded not ‘created’ and is an automated process dictated by the film equipment; therefore, it is often necessary to use other techniques involving variable fps rates to achieve the desired effect. By recording/filming at one speed and playing back or projecting at another, it is possible to achieve slow motion or speeded-up actions.

Flip Book-Flip Book History

A Flip book (sometimes, especially in British English, flick book) is a book with a series of pictures that vary gradually from one page to the next, so that when the pages are turned rapidly, the picture appear to animation by simulating motion or some other change. Flip books are often illustrated books for children, but may also be geared towards adults and employ a series of photographs rather than drawings. Flip books or magazines, often in the page corners. Software packages and websites are also available that convert digital video files into custom-made flip books.

Functionality

Flip books are essentially a primitive form of animation. Like motion pictures, they rely on persistence of vision to create the illusion that continuous motion is being seen rather than a series of discontinuous images being exchanged in succession. Rather than “reading” left to right, a viewer simply stares at the same location of the picture in the flip book as the pages turn. The book must also be flipped with enough speed for the illusion to work, so the standard way to “read” a flip book is to hold the book with one hand and flip through its pages with the thumb of the other hand. Ten German word for flip book-Daumenkino, literally”thumb cinema”-reflects this process.

History

The first flip book appeared in September, 1868, when it was patented by John Barnes Linnett under the name Kineograph (“moving picture”).They were the first form of animation to employ a liner sequence of images rather than circular The German film pioneer, flip book,first exhibited his serial photographic image in flip book form in 1894, as he and his brother Emil did not develop their own film projector until the following year. In 1894, Herman Casler invented a mechanized form of flip book called the Mutoscope, which mounted the pages on a central rotating cylinder rather than binding them in a book. The mutoscope remained a popular attraction through the mid-20th century, appearing as coin-operated machines in penny arcades and amusement parks. In 1897, the English filmmaker Henry William Short marketed his “Filoscope”, which was a flip book placed in a metal holder to facilitate flipping.

Flip books are now largely considered a toy or novelty for children, and were once a common “prize” in cereal and Cracker Jack boxes. However, in addition to their role in the birth of cinema, they have also been an effective promotional tool since their creation for such decidedly adult products as automobiles and cigarettes. They continue to be used in marking of all kinds, as well as in art and published photographic collections.

 

How Animation Works _Why 24 Frames

Scientific Theory of Animation-Persistence of Vision 

Animation is an art and science; it’s a new art form that evolved from technical innovations in frame projector science. Learning the concept of animation will be easy by learning the scientific principle that helps animation work. So what is that principle? It’s very simple and is based on a simple theory-persistence of vision, according to which, a human eye can retain the images for more time when more images are projected at high speed. That means a human eye requires some time to conceive a single image. When multiple images are shown within a less span of time, the eye will retain all images and the result is an illusion-That is Animation.

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For example, multimedia images carries an action printed on them like a rolling ball, with some replacement in the positions of successive rolling ball, rolling in a path in all images. Consider that total number of images is 24, and the time images are exposed to eye is 1 second. That means on an average, each image is exposed one twenty four time of a second and within the next one twenty fourth of a second, the second image will follow. This time it is not enough to grasp all information about an image for the eyes, so the image will be retained for a longer time in memory. When these multiple number of images are retained in the memory, the replacement in their position causes an illusion of motion, like that of a ball rolling.

Why 24 Frames Per Second?

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You can even try 12 frames per second but the action you see will not be appealing. For live action movies the applicable rate is 30 frames per second and for TV animation. any drawing that is produced for an action will be exposed twice. That means, to produce a second of animated action you will need 12 drawings which is equal to 24 frames. The reason is to get some mileage. For features, exposure rate will be in 1’s and it all depends in what kind of an action whether it is a slow one or a fast one. For example, a fast running character should be exposed in 1’s. So that action looks very kinetic. This entire pattern comes under the concept of animation timing. Timing play a major role in animation, especially, in helping it defy the live action movies in extreme action like, Tom and Jerry’s cut to chase sequences. You might have wondered what makes TOM & JERRY performs those extreme action and attain an elastic personality. This is the result of proper application of animation timing.

How to Measure Length of Animation?

Animation is measured in footage. In animation, footage is nothing but length of animation measured in feet. Normally one foot of animation is equal to the length of 16 frames of animation. That means one second of animation is equal to one half feet.

  • 1 foot = 16 frames
  • 1 sec animation=24 frames = 1 1/2 feet.

Frame Rates:

The frame rate that you work at is a very important factor in the final quality of your animation. The frame rate determines how many frames per second are displayed when you playback your animation. If you set the frame rate too high, you have to produce too many drawings. If you set it too low, your animation will look choppy.

12 frames per second (FPS) are recommended for drawn animation. This is one half of the frame rate used by film. This is referred to as ‘drawing on twos’

Typical Frame Rates:

12 fps: The majority of cartoon animation is drawn on twos. When put on film, the frames are exposed twice to make 24 fps. In our case, we can simply play back at 12 fps.

15 fps: Less typical would be animation drawn for twos on video.

24 fps: Film

25 fps: Pal Phase Alternate Line  (European) Television.

29.97 fps: When color was added to the television standard, a slight adjustment had to be made to accommodate the extra signal used for color. The video still plays at 30 fps, but occasionally a frame has to be dropped to keep up. This is called ‘Drop frame’

30 fps: Black and White NTSC National Television System Committee (US) Television.

Animation Techniques

What is Animation?

Animation is the process by which we see still picture move. Each picture is shot on film one at a time and is shown at the rate of 24 picture per second making the pictures appear to move.

Why do we see these image as moving? 

The reason our eyes are tricked into seeing movement can be explained by the ‘Persistence of Vision’ theory.

The persistence of vision theory:

Our brine holds onto  an image for a second after the image has passed. If the eye sees a series of still images very quickly one picture after another, then the images will appear to move because our eyes cannot cope with fast-moving images-our eyes have been tricked into thinking they have seen movement.

The moving Hand Theory:

You can do this by waving your hand in front of your eyes very fast. You will seem to see several hands at once. Try doing this in front of a television screen when it is switched on. You will see even more images of your hand because the television is actually flickering. By waving your hand in front of it you make your eyes very confused about what they are actually seeing.

Basic techniques used in animation:

1. Drawn Animation.

2. Cutout Animation.

3. Model Animation.

4. Computer Animation.

5. Others.

Drawn Animation:

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This covers any form where another replace one drawing in a sequence. Each drawing is slightly different from the one before. It works the way a flip book does. These animated films are made up of thousands of drawing which are shown on screen very quickly one after the other.

Cutout Animation:

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This cover any form of animation where cutout shapes are moved around or replaced by other cutouts. Flat objects like buttons, matchsticks and string can also be used in this form of animation. Cutout can also be laid on top of drawings.

Model Animation:

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This involves the filming of puppets or any form of three-dimensional models. The materials used could include plasticize, clay or wire-in fact anything that can be bent or formed into another shape. The puppets are positioned and filmed before being moved ever so slightly and filmed again. These shots are put together as a piece of film and will give the impression of the models moving.

Computer Animation:

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Animation has historically been produced in two ways. The first is by artists creating a succession of cartoon frames, which are then combined into film. A second method is by  using physical models,e.g. King Kong, which are positioned, the image recorded, then the model is moved, the next image is recorded, and this process is continued.

Using a rendering machine to produce successive frame where in some aspect of the image is varied can produce computer animation. For a simple animation this might be just moving the camera or the relative motion of rigid bodies in the scene. This is analogous to the second technique described above,i.e., using physical models. More sophisticated computer animation can move the camera and or the object in more interesting way,e.g. along computed curved paths, and can even use the laws of physics to determine the behavior of objects.

Animation is used in visualization to show the time dependent behavior of complex systems. A major part of animation is motion control  Early system did not have the computational power to allow for animation preview and interactive control. Also, many early animator were computer scientists rather than artists. Thus, scripting system were developed. These system were used as a computer high-level language where the animator wrote a script (program) to control the animation. Whereas a high level programming language allows for the definition of complex data types, the scripting language allowed for the definition of “actors”, object with their own animation rules.