Shooting green screen/blue screen with an HDSLR camera is somewhat challenging in that you likely have to deal with compressed footage at 4:2:0, which does not treat color very kindly. Since any kind of chroma keying requires reasonable color information, filming on an HDSLR should be considered carefully.

Canon 7D rigged overhead, filming a hand slightly above the blue screen.

We have recently worked on a project that required a hand moving in front of a virtual background. After very basic tests, we determined that in our situation, i.e. the combination of camera format, lighting conditions, and keying software, a blue background allowed for the cleanest key.

While we would normally tend to shoot our HDSLR at the slowest shutter speed possible for the given frame rate, 1/60s left us with motion blur such that the key did not provide us with a satisfactory result. We increased the shutter speed to 1/160s to retain a clear motion look (without image repetition) but avoid motion blur that would prevent us from getting a clean key.

To increase our chances of a clean key, we also removed the subject, our model’s hands, far enough from the blue screen to avoid direct shadows from the hand on the background. Even lighting, i.e. even exposure on the background, increases the effectiveness of any keying software – shadows would challenge the software’s ability to identify and eliminate the key color.

Media M8 producers Scott Miles and Darlene Anderson discuss integration of the project in mobile devices.

Rather than working with the camera native compressed files (h.264), we transcoded the source footage to Apple ProRes 422 in Adobe Media Encoder, which reverses the compression by creating unique, self-contained frames out of every frame in the compressed file. This significantly enlarges the file size, in our case five fold. This process does, however, allow the keying software to work on individual frames, rather than having to access color information contained in other frames of the compressed file.

Hand over blue screen. Note the absence of a hand shadow.

Despite brightness differences on the blue screen, Keylight 1.2 easily eliminates the background.

Despite slight differences in brightness on the background, Keylight 1.2 in Adobe After Effects was able to key out the blue background with only slight adjustments. Even in areas with slight to moderate motion blur, the key was clean enough to be hidden by the actual motion and thus not noticeable to the untrained eye.

Have a look at the finished video:

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