PNG Television: Keying Challenges with ATEM TVS

Using PNG files with alpha channels for keying on the ATEM TVS can present unexpected challenges. A seemingly simple graphic with a soft grey shadow over a transparent background, exported as a 24-bit PNG, displays correctly in various computer applications. However, when used as a downstream key (DSK) in the ATEM TVS (software control 6.6.1), the transparency doesn’t appear as gradual. Instead, a light color cast appears, especially noticeable against dark backgrounds where the shadow should be invisible. Adjusting Clip and Gain settings to 50% and 20%, respectively, yields the “best” but still unsatisfactory result. Using “Pre Multiplied” keying produces significantly worse results.

This issue persists across different graphics software. Creating the graphic in Corel Photoshop X7 and exporting as a PNG produces the same result as using The Gimp. Attempts to save the graphic as a Targa file with explicit alpha from Corel PSP X7 result in no transparency on the ATEM, only a bright background. Exporting as a Targa file from Gimp 2.8 replicates the PNG issue: transparency is not as expected.

The core question remains: is the ATEM TVS inherently incompatible with PNG files and alpha channel transparency for keying, or is there a user error at play? Experimentation with different file formats and software suggests a potential compatibility issue. Further investigation is needed to determine the optimal workflow for using PNG graphics with alpha transparency for keying on the ATEM TVS.