MASKS FOR SAIL

[Updated for QLab 4.1 13 JUL 2017 ]

 

This workspace demonstrates a number of surfaces on a single projector display with surface masks to precisely map content on to a complex  projection surface. This might be a stage set, or as in this example, a complex architectural structure. The example below is programmed in QLab 3 but the downloadable workspace will work in all versions of QLab. You will have to edit the video displays to match your set up.

The Sydney Opera House was Jørn Utzon’s unwitting gift to projection designers, even though when he designed it, the technology didn’t exist to exploit it as such. It has been used for public projection displays many times, most notably in the Vivid Sydney, Lighting the Sails commissions, which have taken place annually since 2009.

In this example I have created 9 surfaces in QLab corresponding to the major architectural features of the building. In the process described I have traced the features from a photograph taken at the projector position, but another approach, that is often used with mapping, is to put a Photoshop canvas live on a projector, and trace the features directly on the actual set or building structure to make the map.

This video shows each surface individually, both in QLab and on the structure (Best viewed full screen)

 

Each Surface is not much bigger than the masked area. This is so that the processor load of each surface is minimised, (content should be made roughly the same size as each surface). Also, if any small tweaks are needed, the corner pins for each surface are close to the area that surface maps, for easy manipulation. All the masks are slightly softened at the edges.

Step by Step Method: This illustrates the creation of the mask and surface for sail 3. First in photoshop, either on a photo taken at the projector position, or live on the actual set or building structure, the outline of the mask for the surface is traced using the pen tool.

01 Draw Path and convert to selection

This is then converted to a selection and filled with white and put on a black background. The layer is duplicated, the original is blurred to give a gradient at the edge of the mask,  and the duplicate is set to darken mode, to retain a hard cut off at the mask boundary.

02 Fills and blur for gradient

The image is than cropped to the mask, with a margin. The image is saved, as a jpeg or png file. Because it’s very Important that the surface size matches the mask size exactly, I always include  the mask dimensions as part of the file name.

03 Save with mask dimensions in filename

In QLab a surface is created, named, and its dimensions set to match the relevant mask. The mask is dragged to the mask well. The grid is switched on and the display device dragged in relation to the surface to place the masked grid at it’s correct position within the multiple mask composition. The surface layer number is then set, so the surfaces stack correctly.

Sail 3 Surface annotated

Here’s a simulation of the final result  ( I have never actually been to Australia, or projected anything on to the Sydney OperaHouse.)

 

You can download the workspace and associated files here

Further reading about projection mapping including details of how to map an already warped QLab surface can be found in the chapter Mapping Complexities

Original Image:”Sydney Opera House Sails”. Licensed under CC BY-SA 3.0 via Wikimedia Commons  Modified images by Mic Pool distributed under the same license. Video Images in demo video © Mic Pool 2004 – 2015 All Rights Reserved.

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