Shooting behind chroma key backdrop
Do you want to take a snap of you in front of Statue of Liberty, while being in Delhi? Do you want to shoot your video showing that you are riding a camel in front of a pyramid in Egypt, while being in Mumbai? You might say that I am crazy. But, yes, this is possible in this world of technology. With the aid of some technological tools, you can remove the original background of an image or video with anything. This is known as chroma keying, which is nowadays very commonly used in film and photography industry.
Chroma keying or chroma compositing is process by which a color range is selected on an image and deducted, leaving the selected range transparent. When this image is merged on another image, the background image becomes visible through the transparent zone. Hence, the background of the original image is changed.
Firstly, the foreground image is shot in a blue or green cloth backdrop. This is because these two colors differ quite distinctively from human skin tone. The croma backdrop should be even and uniform. Green croma key background is preferred while using digital cameras because the digital cameras are much more sensitive to green color than blue, as the pixel density in green backdrop is high, thus creating less noise. Moreover, less light is required to illuminate green key backdrop . Then in the post production step, which can be done in Photoshop, final cut pro, etc., the background color range is selected and subtracted. Then this image is set over another image selected as the background and merged.
The most important factor of chroma keying is the lighting of the backdrop. Lighting has to even and uniform in all zones, so that the color range of the background stays low. If there is any shadow, the color range will become wider as the shadows create darker shade. Subtracting wider color range may affect the subject of the image.
Another important element is to adjust to the correct exposure of the camera. Overexposures or underexposures may result into poor saturation level and high noise. So, proper lighting has to be done to get the desired image. Also there had to be good contrast in between the subject and background.
Creating the setup
Make a screen with a green or black cloth. The screen should not be of reflective material.
Ensure the screen is smooth and even.and holding it on backdrop stand
Do proper lighting. Give right amount of light and ensure that the background is neither burned, nor dark. The lighting should be thoroughly even in all zones.
Study light of the desired background image.
Lit up the subject in parity with the background image.
The images should be of proportionate size to maintain the depth of the field.
Make sure that the subject does not have any color similar or close to the backdrop.
Rely on aperture sizes than ISO or shutter speed to obtain the best color.
So, now you have known the technique, let’s start it. Take a snap of yourself on a green screen. Open it in photoshop. Select the green color range and extract. Now you get your image with a transparent background. Find a photo of Grand Canyon. Set it as background layer. Copy your transparent image and paste it on the Grand Canyon layer. Resize, move you image (layer 2) to get a realistic picture. Merge the two layers, and your photo is ready.