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This part of computer animation deals with frame by frame a videotape, animation which can be created using the graphics hardware, even with the desktop computer. A videotape recorder or a movie camera with a single frame exposure and a dark room are the prerequisites for this type of computer animation.

This method is used for production of sophisticated graphics. A single frame containing the animated pictures can be generated using this computer animation. When the recording of a movie or a videotape is to be displayed as the single frame been the single picture is completed in a frame buffer. This type of animation has certain problems as there is intermediate production of an optical picture on film with the possibility for disturbance and noise. If the light level of the room changes then the brightness of the monitor can also undergo slight changes over the long time periods. These changes can be aggravated by the filming itself and then the film is played the changes are evident so a room with stabilized light is important.

The production of an intermediate optical picture by recording the content of the frame buffer that it the on one magnetic track on videotape is completely avoided. But there also there are many difficulties.

The signal stored on the videotape and the color TV broadcast signal is identical. And this is composed of different type of information such as luminance, hue, horizontal synchronous pulses, vertical blanking, the reference black level and saturation. This is known as NTSC Composite video signal where one TV frame is composed of two interlaced fields. And 262.5 horizontal scan lines are present in each field and 525 interlaced scan lines are present in the whole TV frame. 60 fields per second which correspond to 30 frames are carried by the composite TV signal.

The present days videotape recorders are of helical type. The magnetic reading and writing heads are placed on the spinning cylinder around which the magnetic tape is pulled in a slanted track. The speed of rotation of the spinning cylinder and the magnetic tape depends on the type of the machine.

In most of the video recorders of today one field per track is recorded. The read and write head of the cylinder rotates at 60 rpm. The cylinder is wounded almost completely but the magnetic tape depending on the recorder type.

The tape is pulled over the cylinder in the slanted position when the cylinder is rotating and in the same manner the video track is written or read in a slanted path across the tape. These are only the video signals. For recording the audio signals the other heads are needed to record on the special audio track. Recording for the pulse of each frame is also made. Later on a binary time code for each field can be added through certain devices. In videotape editing for finding and identifying individual fields this is very important.

The C type recorders in which the magnetic tape is wrapped around the spinning cylinders are the best quality video recording devices through which the best quality output can be achieved. One inch wide magnetic tape is used in these types of recorders. A video cassette recorder generally produces low picture quality recording as in these the magnetic tape is not operated on an open reel but is enclosed in a cassette and is only ? inch or, half an inch wide.

If the single frame stored in the frame buffer of a graphic system is to be recorded then the output from the frame buffer to the monitor is done in many different ways. If this is only an RGB signal that consists of three separate signals for green, blue and red color with synchronous pulses on the green, then they must be transformed into the NTSC Standard which is recordable on the videotape. Middle Price range graphic boards can produce an NTPC composite video output. A feature known as genlock feature is needed to tie the frame buffer?s scanning rate to the rate of the recording. In the circuitry it is important to have several number of scan lines for a frame buffer while the NTSC frames always have 525.

Now with the changing scenario today there are many digital video recording devices have come up with which these jobs can be done with much ease and the precursors of these were RGB video cameras which stored the information in the form of RGB code rather than the NTSC composite. In RGB video cameras the storage of red, blue and green intensities and the horizontal synchronous signals is for each scan line. An RGB monitor or a converter to produce the NTSC signal for a TV screen is required to playback such a tape.

Now question of storing the frames in the memory arises. The computer graphics screens for the low priced desktop computers allow watching complicated animated scenes. An example of this is juggling robot on the Amiga computer. Here the scenes are created by ray tracing as the single frame is too complicated scene. The robot is constituted of many spheres which overlap partially and do not reflect. The robot juggles the reflecting spheres which cast shadows on the ground. This is a frame by frame animation consisting of 20 frames within a second.

In CAD/CAM applications or in paint and draw programs the real time animation is present on the screen in the form of rubber band lines, growing rectangles etc., with the movement of the input devices. The animation in such cases is created by rapidly drawing, erasing and then redrawing the figures in question. This concludes the last part of the computer animation.