The costs and problems of overlaying multiple images on one screen to form a seamless large image are well known. Lessons learned from slide projection have been used to derive presentation tools such as Watchout. However, these are expensive and overkill when smaller projects need simple joins or permanent installations need only to render the joint once and replay it many times. Existing tools also can’t cope very well with distortions and real world site projection issues.
When faced with the challenge of needing to join two live video images on a curved screen, we realised that the key to solving these problems was to produce site specific gradient masks that could be composited into a final video. What was lacking was a tool that allowed masks to be made and tested in real time without having to re-render video clips every time the mask was tweaked. Software was written in house that used a multiple head graphics card to produce two overlapping customised test card images, with the mask generated algorithmically. The size, position, gradient type and gamma of each projected colour can be separately adjusted in the mask using a configuration file until a seamless join is achieved with the testcards. Each test takes just a few seconds to iterate rather than minutes or hours to render a video file. The resulting final gradient is then exported as a bitmap and composited with the real video footage to be used as the final product.