One of the most interesting and exciting areas of film/video production is creating SFX sequances. The ability to manipulate the world that we see, from creating a twin using mirrors to flying spaceships using complex 3d computer animations, is something the director has to find a way to create convincingly, and at price which the budget can afford. Computer SFX are the in thing now, and they will remain that way becouse they are the best way of doing complex FX (or in some shots the safest way).
Check out my SFX Projects_Index pages on how to use some of these effects in your own videos !
*I will try to add some graphics to illustrate the effects when I have some more time.
Double Exposure - This was one of the first special effects ever created. All you do is film one shot on your camera, rewind the film and film your second shot. What you should get is two seperate imagesmixed together. This can be done on video, but only in editing or mixing live between two cameras. The best way to get this effect is for the actor/model to be in front of a black cloth (ie, curtain or wall) and to be standing on one side of the screen so the images do not overlap (unless you want this effect). In this way you can have a model spaceship flying around the head of an actor, or a ghost walking through furniture.
Jump Cut - The classic way of making things vanish is to film the actor/prop, stop the tape/film (or cut the gap when editing), remove the actor/prop from the shot and start the tape again. The camera should be locked off (not moving) otherwise the background will move between the cuts.
Mirrors - It all used to be done by mirrors, but computers have taken over. Strategiacally placing a mirror between the camera and actors gave the illusion of split screen fx, (ie, two people talking to one another on a phone).
Models - Virtually every sci-fi film relied upon models to create spaceships. These would be made out of everyday objects (BBC tv's Blakes 7 liberator was made out of old washing up bottles) or custom made out of special plastics or foams. The models are literally filmed in front of a camera, often placed in front of model landscapes, much like a model railway. If you cannot afford computer graphics, then models are a good way of creating spaceships, and can be fun as well. Not all models are small, some are huge, like the volcano mouth created in Dante's Peak which was built to be blown up.
Stunts - Sometimes the only way to get an effect is to actually do it. Car crashes for example have to be actually performed by stuntmen, as models will not give the desired effect. The same is true of high falls and crashing through windows. You should never try performing stunts yourself, unless you are properly trained, you will injure yourself, or worse! One stunt you can perform is breaking bottles over your head. Normal glass shatters into sharp shards, stuntmen use sugar glass which breaks into harmless pieces. You can buy these breakawy props from SFX stores, but you must use a bottle which is designed for stunt work.
Backdrops/Back Projection - Before chroma-key came along the only way to make an actor appear in another place was to stand him in front of a large painting of a scene. As technology progressed the painting was replaced by projecting an image onto a screen, which allowed moving backdrops rather than staic paintings. This opened up new oppurtunities for film makers, especially with car chases. A camera films out of the rear of a car, the film is then projected onto a screen in a studio behind actors who are sat in a car and it looks like they are driving. Back projection is still used on low budget tv series, such as Murder She Wrote. The techniques has since been improved, in the rail crash scene from The Fugitive Harrison Ford jumps from a bus just as a train ploughs into it. The train crash was real, but obviously too dangerous for Ford to really jump, so back projection was used, with Ford jumping from where the bus seemed to be (really a platform) with smoke and lights in the foreground to add to the illusion.
Transitions - A transition is used to switch from one shot to another, and is split between two types, a mix (or dissolve) and wipe. A mix is where two images blend into one another when switching from shot to shot, a wipe is a line moving between the shots. The basic wipe is normally a horizontal/vertical line crossing the screen to switch from shot to shot. As technology advanced the wipes became more elaborate until finally you get the MTV and Top of the Pops style effects seen on pop videos.
There are some examples of the Premiere Transitions here.
Chroma Key - also known as Colour Seperation Overlay (CSO) or 'blue screen' is the most common effect used in the media today. Actors, props or models are placed in front of a large blue (any colour can actually be used, but blue and green are the most common as they do not interfere with flesh tones) screen, a computer then replaces the background colour (the blue/green) with another picture source. In video this can be added live, such as in weather forecasts. Film has to have this effect added during the editing, as the film has to be processed first. it is possible to buy a vision mixer which can do this effect for around £2,000 or so, (my college uses a Panasonic MX50). Most non linear editing packages (ie, Adobe Premiere) have a chroma-key facility.
Go-Motion - Star Wars created new technologies in the SFX world, and saw the birth of ILM. Go-Motion is the reverse of animation where rather than moving a model and camera one frame at a time, you allow the camera and model to move in real time.
Composites & Mattes- these are mainly used in film and are the forerunner of rotoscoping and CSO work. In Indianna Jones & the Temple of Doom Harrison Ford stands at the mouth of a mine which looks out from a cliff face. The mine entrance is real, and Ford stands in this set, but it is not really in a cliff face. A painting of a cliff face is created and the two are blended together. The blend is created by a background & foreground mask which block out the unwanted areas and allow the two to be combined in a special form of double exposure. It is a very complicated process and I will try to find some illustrations for this page. The computer has made hand drawn mattes on film obsolete as CSO and rotoscoping now do the job.
Rotorscoping - This is a more complex computer SFX. The shot is digitised onto a computer, and each frame is altered by hand, literally painting on the frame. This is a basically a form of animation, but you are altering a feature, or adding one to the film. This is very time consuming as there are 24 frames per second in film, (25fps in video), and they all have to be touched up individually, so a 4 seceond shot can take around 100 frames to alter. Adobe Premiere can export video clips as a format known as Filmstrip, this can then be altered by Adobe Photoshop and sent back to Premiere for putting onto video. Strata Media Paint and Metatools Painter can also rotoscope on individual frames, as can the more powerful Commotion and Paint* programs.
3d Graphics - Film makers were quick to utilise the computer for creating complex objects such as spaceships once the technology had grown powerful enough. Jurassic Park was the turning point as it was then possible to create living, fluid moving creatures, as opposed to spaceships. Toy Story then took it to the next level by creating an entire computer generated movie, something which had never been attempted before. It was now possible to create fx which were too dangerous to recreate naturally (ie, Tornadoes and Volcanoes in Twister and Dante's Peak) , or too expensive to create with the real thing (the fighter jets and Air force One over Area 51 in Independance Day). There are plenty of 3d software programs out there for home computers such as Infini-D which is what I use.
Sound FX - Not all special FX are visual, sound is essential to making a SFX scene look real, ie, the roar of jet engines or an explosion. Sound FX can be created by anything. The laser blasts in Star Wars were created by recording a metal pipe hitting a steel wire (like a telephone pole support wire), and the Jurassic Park dinosaur roars were created by altering animal noises on a computer. you can get sound FX from pre-recorded CD's (the BBC do a good range) or from the internet.