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How to Do a Video Matte Shot Using Chroma Key

Updated on September 13, 2011

Hollywood Special Effects

In the old days of Hollywood, the special effects artisits devised a method for enhancing the surroundings of a scene without the added cost of building a large set. It was called a matte shot.
The special effects artist double exposed the film to create an illusion that a matte painting and live action were one large scene and taking place at the same time. This technique involved blacking out an area on glass so that an area of film remained unexposed to light. Black paint on glass was one of the popular methods for performing a matte shot. Using black paint was often utilized when the matte shot angles were irregular. The effects artist watched carefully through the lens as black paint was applied to the areas to be blacked out.
Be sure the black paint is flat and does not carry any reflection value. Light reflection will cause problems in post when applying the chroma key method. Today using a visual monitor jacked into the camera yields the same results. The visual effects artist can watch his or her progress on the monitor as an area is carefully blacked out. The live action is exposed on the film by placing the camera behind the glass and shooting the live action through the glass. The exposed part of the film is then double exposed by masking out the live action area using the color black and then filming either a painting or model onto the original unexposed area. This resulted in a composite picture when the film was developed. The live action and the painting or model melded together into one solid picture.
This same method can still be performed today digitally using a simple chroma key function. Either by using a mixer or through a software product on the computer. These are the basic steps for shooting a Hollywood matte shot. Any color may be used for the chroma key filter, but be aware that black does work best since it does not reflect light and cause problems with color continuity.

Things you will need
1. Video Camera
2. Tripod
3. Black poster board or black paint
4. Sheet of glass
5. A stand to hold the glass
6. Paint brush
7. Tape measure
8. Writing tablet
9. Pen or pencil
10 Digital still camera
11. Mixer or chroma key software

Set up the glass using a stand to support the glass in an upright position. Place the camera behind the glass and either view through the camera or monitor to observe the areas where the black paint will be applied. After the black paint is applied allow it to dry so that no light is reflected back to the camera.
Before the shoot takes place be prepared to take a few notes: Using the tape measure, take a measurement from the tip of the camera lens to the front of the glass. Write down these measurements. Take a measurement on the tripod height from the ground to the tripod camera mount. Record these measurements in the tablet. Measure the tripod tilt on the head. Most tripods tilt mechanisms are graduated in degrees. Write down the tilt if any. Record the time, day, month, and year. Take a reference photo to record the outside conditions. This can be valuable reference material to the effects artist if the matte shot is performed at a later date and time. The weather conditions for the model and painting should match the weather conditions of the live action. The settings will provide a guideline for duplicating the same conditions in the studio.
Prepare to shoot the live action through the glass after the black matte is properly prepared. Be cautious not to capture the outer edges of the stand or other outer surroundings in the footage. Consider that the glass itself has a high reflection value and the camera man and camera’s reflection can be caught in the glass during the matte shot. To avoid a retake have the camera man dress in solid black including black gloves and ski mask, and drape a black cloth around the tripod and camera leaving only the camera lens exposed. It is important to remember that the camera and the tripod remain fixed through the entire shoot. Moving it results in a retake. Having the camera pan, tilt, or zoom results in the live action not matching the painting since the painting would remain motionless spoiling the matte shot. After suitable footage is taken bring the footage back to the editing suite for the final touches for completing the matte shot.
Save the recorded live footage as a file in the computer. Duplicate the camera position and glass using the recordings from the tablet. The matte shot is completed by either painting a scene in the black area of the glass or by placing a model behind the black area of glass. If a model is to be used, use a fine edge black marker to outline the outer edges of the black matt. This is done because once the paint has been removed and the model s placed behind the glass the other portion of the glass is painted black where the live action has been previously recorded. Carefully scrape the black paint from the glass leaving the black marker in place. Place the model behind the glass and paint out everything below using black paint. Be sure that when a model is used that the outer conditions in the live action and the model conditions match, such as shadow position.
The model is ready for filming. Film the model through the glass. The footage is now ready to render into a composite shot using a simple chroma key function. The live action will be source A and the model will be source B. Bring up Source A on the screen and using the chroma key function and click on the black portion of the live action scene and use source B as the replacement for the black. The matte shot is complete. If the black paint had not been added to the lower portion of the model whatever background on source B would bleed through rendering the matte shot useless.
The method for using a painting to complete the matte shot slightly differs. The painting is painted onto the black area of the glass and the clear area where the live action was filmed is now blacked out and ready to film. Use the same method for using two files and the chroma key function to complete the matt shot.
This simple method takes a little practice. Do not be afraid to deviate from tutorials and experiment when it comes to creating special effects.


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