Making A Scene
Decided to make some artificial datasets for my project. CGI renderings where the camera moves through the scene, in which I can control the lighting perfectly and generate 100% accurate ground truths without having to colour them in by hand as with natural imagery.
Used Blender for the first time; it's like stepping into a jumbo jet cockpit. I've learnt how to use it enough for my purposes though. I now have a couple of artificial scenes and accompanying ground truth sets:
Got ground truths by disabling all textures, reflections etc., colouring all objects in a uniform grey that emitted grey light (so no shading) and still cast shadows. The shadows in the second image (ground truth) should all be pitch black without any fading in or out, but I've solved that issue by counting any pixel value that's not white (background colour) or value 153 (grey, object colour) as a shadow in my ground truth checking code.
Despite being artificial, these are still challenging environments, with fog, ambient occlusions, a mixture of soft and hard shadows, different types of lighting and colours, textured objects with highly contrasting patterns, glossy/shiney/mirrored surfaces, and completely dark areas (which are technically shadow, but I think they're unlikely to be detected as such by most of the detection methods I try next).
The simple thresholding tests I've been doing are therefore no better than they are on the real-world Pioneer images, with far too many false-positives for shadows...
The simplest artificial scene I made was simply a white background with grey cubes casting hard black shadows:
(In that scene, the input images double up as the ground truth images).
So yeah, more conclusive evidence that the dumbest approach to shadow detection is the dumbest. MORE GRAPHS NOW
(It's like cupcake sprinkles :D)
Now, I'm going to move on to better shadow detection methods. Colourimetric ones first -- in the RGB colour space to begin with, and then experiments with other colour spaces which may be able to separate luminance from colour better.
