Vol. 16, No. 3, Oct-December 2005 

Tech Tips for Practicing Laserists

In recent years “30K Scanning” has become the industry buzzword. Laser projector components such as scanners and computers as well as complete laser projection systems are now regularly specified and sold according to standard specifications using terms like “ILDA 30K.” But there is much confusion and misunderstanding regarding the use of this term. There are actually several separate concepts critical to proper show creation and playback which get mixed up in the term “30K.”

Confusion among these concepts has lead to large and small show disasters. In a sizeable production earlier this year, a new laser display company contracted with a third party producer to create artwork for an upcoming corporate laser show. The new company specified that the show be created for ILDA 30K and that no flicker be present in the art. The new company then carefully tuned their scanners to properly reproduce the ILDA Test Pattern at 30K.

The offical ILDA Test Pattern.

Receiving the artwork in digital file form just before the show, they played it back and, to their horror, experienced dramatic flicker in a show that cost them several thousand dollars. The corporate client was unhappy with the flicker and only paid a portion of the bill.

Tuning vs. Scan Rate
What happened? The company that created the artwork used the ILDA 30K standard properly and created a fine-looking show, but the company that played back the show did not understand an important part of the playback equation. Even though the playback scanners were tuned to ILDA 30K, the playback computer was sending out show data at a much slower speed: 12K. If the playback computer’s output rate had been set to 30K, the flicker problem would have been eliminated.

Another example involves a laser production department that had its primary digitizing scanners retuned to a different scanning speed during the process of hand digitizing a several hundred frame animation sequence. The artist thought that because the images would all be played at 30K, it didn’t matter where the scanners were tuned for digitizing.

Because of this change in scanner performance, the digitizer was unknowingly compensating for the new scanner tuning as he entered the data for each new frame. Most of the frames that were digitized after the retuning looked bad, and hundreds of hours of work were wasted because of the inconsistency in scanner tuning between frames. To avoid these costly mistakes in the future, we need to understand some basic technical concepts relating to the tuning of scanners and the playing back of laser show data. Finely tuned scanners will produce less than stellar results if they are sent data at the improper speed. Likewise, the best digitized images, even if played back at the intended speed, will look second-rate if the scanners are not tuned to the proper specification.

Points: Keeping the Score
One of the most used terms in the discussion of scanner performance is “30K,” which is shorthand for 30,000 points per second (30K pps). Laser computer systems generate laser graphics by outputting XY data points sequentially. This data is used to move the scanners in the horizontal and vertical (X&Y) axis to draw laser graphics. The laser spot traces the path of these points very quickly. These points are blurred into lines in the eye of the viewer.

The rate at which these data points are output is defined as “points per second” or “pps.” 30K therefore indicates an output rate of 30,000 points per second from the computer (or other signal source). This is the technical origin of the term. Other terms used to describe the rate at which points are output include “scanning speed,” “scan rate” and “point rate.”

The next concept to understand is the use of test patterns. The ILDA 30K Test Pattern relates to a specific tuned performance of the scanners. Scanner speed (step response) and damping dramatically affect image quality and can be adjusted across a wide range by changing the servo gain and damping potentiometers in the scanner’s electronics. If scanners are not properly adjusted, graphics created on one system will not playback correctly on another. All of the scanner’s parameters can be adjusted to industry standard performance with the use of the ILDA Test Pattern frame.

Too Many Terms?
To achieve proper scanner adjustment, the ILDA Test Pattern frame is displayed at a specific scan angle and at a specific point output rate. The scanner electronics are then adjusted until the test pattern appears correct as scanned in laser light. The ILDA 30K Test Pattern, for example, must be projected with a point rate of 30,000 points per second. Likewise, to tune to the earlier ILDA 12K Test Pattern the point output rate is 12,000 points per second.
Other terms that are sometimes used to describe scanners tuned to the ILDA 30K Test Pattern are: “30K,” “30K Tuning,” “30K Scanning,” “ILDA Tuning,” “ILDA Scanning” and “ILDA Test Pattern.” Although these terms may not be technically correct in their usage, they have unfortunately entered the industry vocabulary. In the case of the last three terms, use caution, as they do not define to what standard, if any, the scanners are tuned (for more information on the use of the ILDA Test Pattern see the Test Pattern section of the ILDA Handbook and Technical Standards).

To add to the confusion, laserists creating artwork will often refer to their programming as “30K” without clarifying what they actually mean. The term “30K”as applied to artwork usually means that the artwork was digitized and programmed on scanners tuned to the ILDA 30K Test Pattern.
This being the case, the laser graphics will look as intended if played back on scanners tuned to the ILDA 30K Test Pattern, assuming the show playback point rate is also set at the correct speed. The terms scanner tuning and show playback point rate, however, can cause confusion.

As mentioned previously, “point rate” refers to the how fast the computer outputs the image data. It is important to note that this point rate, (also referred to as “scanning speed” or “scan rate”), is usually independent of scanner tuning.

While a show may be programmed for display on scanners tuned to the ILDA 30K Test Pattern, the actual point rate intended for playback may be higher or lower (and may even vary within different segments of the show). The use of the scanners tuned to the ILDA 30K Test Pattern does not necessarily imply that the show playback point rate should be fixed at 30,000 pps. If you want to playback a show correctly, you need to know both the intended scanner tuning and the intended point rate.

The issues concerning point rate from computer sources also apply to other digital playback systems. However, the point rate on some playback systems (such as the Alesis ADAT) is fixed at recording and cannot be changed significantly at the time of playback.

What about 12K? Because the 12K and 30K standards are based on the same test pattern, laser graphics created with properly tuned 12K scanners can be played back and look identical on 30K tuned scanners in most cases. Conversely, 30K images can be displayed on 12K tuned scanners and look correct with a proportional decrease in scan rate. However, when scan rates are reduced to this level, an image with even a moderate number of points may flicker dramatically.

In the future, when a vendor states that something is “30K” be sure you understand exactly which parameters they mean to ensure a successful show.

Stack is a former chair of the ILDA Technical Committee and introduced the Test Pattern to ILDA (the pattern itself was originally developed by Robert Mueller). Today, Stack heads a laser display consulting firm in Utah.