creating touchlines

The first systems we used at Palindrome were simple sound triggers, the so called 'touchlines'. They detect the presence of a bodypart or object in a certain fixed location along a line.

In the leftmost column of the Element-Editor there are creation-buttons for the Eyecon elements. Press Line to create a new touchline. A new line entry in the element list is made. In the video-window the new line is displayed in the upper left corner. A touchline compares all the image pixels that are covered by that line with a stored image of the scenery, usually the empty stage, empty room etc.

Moving the touchline.

Move the touchline by moving the end points of the line. Click the end point with the left mouse button, hold the mouse button and move one end of the line. You can also move the whole line by grabbing the line between the endpoints.

Assigning a note

Now you can assign a midi-synthesizer note to the touchline. Select 'Single' in the Midi-Notes setup page. By default 'No note' is selected. By default the note 60 (C3) is selected. You can change that value in the combobox 'Note From'. If you want to assign a whole range of notes to the line you have to remove the 0 in the field 'Scale' (actually this is a confusing step). Now you can use the field 'Note to' to set the note or the endpoint of the line.

Testing the touchline in simulation mode

Below the video picture you find four tiny boxes. They can be moved around by dragging them with the right mouse button down. When you touch the line the assigned sound will play.

Background Picture

Before you may switch to run mode you have to take a snapshot picture of the empty stage. In 'run mode' the current video image is compared to that reference picture. Changes in the image are used to trigger the media elements. To capture this reference or background picture you have to click on the Backgound-Button in the control-window. Whenever you press this button, EyeCon switches through all the connected videocameras and stores individual backgound pictures for each channel.

Testing the touchline in Run mode (from Video)

Press in the control window and try to physically reach the touchline in the camera picture.

Is the note playing? If not, check the Midi-Note page setting for the midi port. Usually a sound board has multiple midi ports. One or more for the internal sound section, one for the external midi interface. Make sure an internal synthesizer is selected.

Playing Scales

Now let's play more than one note with the touch line. And also use a different sound patch. The sound patch can be changed by opening the Patch combobox and selecting one of the General Midi Instruments. Maybe Marimba. Now go to the Edit field called 'Scale' It has a 0 in it. You can enter a list of numbers which stand for the semitone distance to the Base-Note you select in the field 'Note From'. The numbers are separated by commas. Entering 0,4,7,12 is laying out the notes of a major chord along the touch line. Try playing it. If you delete the whole 'Scale' entry, the Field 'Note To' becomes available. When you select 'C4' for example, than all chromatic notes between 'C3' (Note From) and 'C4' (Note To) are layed out along the line.

Possible Problems

- wrong or no trigger

Maybe the sensitivity of the touchline is too high (randomly playing even if not triggerd) or too low (just sometimes playing even if it should be triggered). One basic setting is the so called pixel threshold in the control window. When EyeCon compares a video picture with the stored background picture it looks at the brightness values of each individual pixel and calculates the brightness differences between the pixel and the same pixel in the background. If the difference on any of the lines pixels is higher than 'pixel threshold' than EyeCon assumes that the touchline is triggered. Depending on the light situation you have to adjust the pixel threshold. A value in the range from 60 to 100 is a good start. Under bad circumstances like low lighting and noisy camera picture you might have to use values up to 250. In some situation i was able to use values down to 30 which makes the system very sensitive.

Another cause for oversensitive behaviour of a touchline is if the line crosses very high contrasting object edges. In that case even the slightest movement of the camera or some signal jitter in the video-connection leads to high brightness changes in the pixels at the contrasting edges. Try to avoid these situations.

- no sound

If you don't hear any sound check which Midi-Port you are using. In the Midi output window you find a combobox which list all available port. There are usually ports for internal sound synthesizers and also ports for external midi equipment. Select one of the internal synthesizers.

Also check the computers volume mixer settings.