In our experiment, four cameras, Philips SPC900NC, are mounted on the screen in horizontal and tilted direction separately. Philips SPC900NC has 640x480
resolutions, 1300000 sensors, and are connected with computer by USB2.0. Black paper are used as the frame of screen, and PC is tested with Intel CoreTM2 Duo CPU running at 3.00 GHz and 3.25G RAM.
(a)
(b) Figure 5-1 :Experiment Equpment
(a) System overview (b) Cameras upon the corner of screen Cameras
Frame of Screen
Horizontal Cameras
Tilted
Cameras
We then compare the accuracy of our algorithm with different screen content and object number by projecting them on different screen with projectors. In the first test, white background is projected on the screen. The second test is in multi-touch application progress. The least test would then detect objects when cartoon is playing on the screen. All scenes would be tested with 2 fingers restricted and with unlimited number fingers. The actions would be general gestures used in application - rotate, zoom-in/out, move or any other types of existing gestures. Then, we test the computation time of algorithm of different number of objects.
(a) (b)
Figure 5-2 Different screen contends of experiments
(a)White background (b)Multi-touch application (c)Playing Cartoon
(c)
(a)-1 (a)-2
(a)-3 (a)-4
(b)-1 (b)-2
(b)-3 (b)-4
(c)-1 (c)-2
(c)-3 (c)-4
Figure 5-3 Images from camera in experiments (a) Test with white background
(b) Test with multi-touch application (c) Test with cartoon
( )-1 Right horizontal camera’s image ( )-2 Left horizontal camera’s image ( )-3 Right tilted camera’s image ( )-4 Left tilted camera’s image
Table 5-1 Accuracy of different experience
Test 1 Test 2 Test 3
Limited object no more than 2 97.85% 96.53% 87.5%
Un-limited object number 90.06% 84.14% 81.15%
The test with “limited object no more than 2” is test with 500 frames, and
“un-limited object number” is test with 100 frames.
Because the latency of IO is depend on the input and out method, we focus on the latency of our system without IO part.
Table 5-2 Latency for different number of object
1 2 3 4 5 6
Latency(ms) 1.934 9.540 16.099 22.039 26.229 29.950
The latency is calculus from 700 frames of each number of objects. The latency is the mean latency of five time processing.
From the result, we confirm the latency of our system is not strongly affected by the number of touch objects.
Latency of different number of objects
Chapter 6. C ONCLUSION AND F UTURE W ORK
In this thesis, we build a new type multi-touch system which can be applied to large-size screen. This system is able to be applied to various sorts of displayers and integrated with many legacy multi-touch applications. Our system uses horizontal cameras to enumerate possible positions on the screen. Then, those positions would be analyzed with the tilted cameras which are set upon the horizontal cameras. The objects would be separated from the ghost by arrangement process, which is speeded up by Viterbi algorithm and variance-include arrangement. Both algorithms are pre-decision algorithms, but the former would not affect the arrangement accuracy. In the last step, the existed objects are tracked and sent to the application with TUIO protocol. Besides, the system stability is confirmed by experiments in different situations.
There are two methods to speed up the processing, replacing the webcams by typical cameras or re-writing the program with multi-thread. The color in-consistency should be deal by analyzed raw data from camera. Thus, separating horizontal foreground by tilted view can be put into practice without the color in-consistency problem.
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