[argyllcms] scanin and perspective distortion
- From: "Guy K. Kloss" <G.Kloss@xxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 6 Feb 2008 13:17:11 +1300
Hi,
I've experimented a bit with the scanin tool for reading characterisation
targets. As the use targeted case here involves digital cameras (still &
video) the capturing of the target is not as trivial as for e. g. scanners.
Of course, the image needs to be captured in a way that no specularities or
any kind of glare is present on the target. This can be achieved by either
changing the positioning of the camera, the illumination or the target. For
many cases however the characterisation is to be performed in the geometric
conditions as given by a fixed setup in a fixed location (towards windows,
lamps, etc.). So the only way to remove glare is to move or tilt the target
relative to the camera.
Doing this I have discovered the following, which is not an issue for scanners
as input devices. The scanin tool seems to be relatively robust towards pure
rotation and (uneven) scaling as long as it is along the target's axes. For
testing I've created a few test samples. These are the problematic
circumstances:
* perspective distortion
* pin cushion type distortion
* rotation with uneven scaling
(or scaling along a non-main axis of the target)
The issue is now, that any image distortion that leads to a non-rectangular
shape of the target potentially endangers the characterisation, as pixels
outside the patches (or belonging to other patches) will be evaluated. This
means that the target MUST remain orthogonal towards the visual axis of the
camera, with only limited pin cushion distortion of the optical system.
Any clues on solving this problem either in software or in handling the test
setups? If bad comes to worse I've got to dig deeply into the OpenCV tricks
box and try to undo certain distortions of the image before the
characterisation process. However, I'd rather like to avoid that to not
induce a higher error than necessary.
Guy
--
Guy K. Kloss
Institute of Information and Mathematical Sciences
Te Kura Putaiao o Mohiohio me Pangarau
Room 2.63, Quad Block A Building
Massey University, Auckland, Albany
Private Bag 102 904, North Shore Mail Centre
voice: +64 9 414-0800 ext. 9585 fax: +64 9 441-8181
eMail: G.Kloss@xxxxxxxxxxxx http://www.massey.ac.nz/~gkloss/
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