Editing Chroma key (section)

===Even lighting===

[[File:Myx tv.jpg|thumb|right|267px|A live broadcast of [[Myx TV]] using green-screen chroma key. Note the lack of shadows on the screen. The whiter area near the center of the image is due to the angle this photo was taken from, and would not appear from the video camera's angle.]]

The biggest challenge when setting up a blue screen or green screen is even lighting and the avoidance of [[shadow]] because it is best to have as narrow a colour range as possible being replaced. A shadow would present itself as a darker colour to the camera and might not register for replacement. This can sometimes be seen in low-budget or live broadcasts where the errors cannot be manually repaired or scenes reshot. The material being used affects the quality and ease of having it evenly lit. Materials which are shiny will be far less successful than those that are not. A shiny surface will have areas that reflect the lights making them appear pale, while other areas may be darkened. A matte surface will diffuse the reflected light and have a more even colour range. In order to get the cleanest key from shooting green screen, it is necessary to create a value difference between the subject and the green screen. In order to differentiate the subject from the screen, a two-stop difference can be used, either by making the green screen two stops higher than the subject, or vice versa.

Sometimes a shadow can be used to create a visual effect. Areas of the blue screen or green screen with a shadow on them can be replaced with a darker version of the desired background video image, making it look like the person is casting a shadow on them. Any spill of the chroma key colour will make the result look unnatural. A difference in the [[focal length]] of the lenses used can affect the success of chroma key.