We are seeing major improvements in the quality of movie presentation. Examples are the larger screens, stadium seating , torus screens and improved auditorium design.
The improvements require new levels of performance from lamp-houses, projectors, lenses and screens. As the performance improves, we also need to improve our measurements and measuring techniques.
For example, the measurement of light level and light distribution on a screen, especially a large screen, is a time consuming and rather tedious task. This becomes a rather important consideration when adjusting a lamp-house and projector to illuminate a 73 foot screen.
Picture steadiness, flicker and contrast ratio also come under greater scrutiny as we improve performance. Large screens and stadium seating tend to emphasize any deficiencies.
It seems that everywhere you look, a new theater complex is being built. There seems to be a proliferation of new screens. Yet there is the increasing pressure to keep the cost of operation down. This means that our technically qualified technicians have to cover more and more screens. In some cases, the theater staff is changing Xenon bulbs and making adjustments to their lamp-houses. We need to simplify and expedite the measurements and adjustments.
Presently, the standard method of measuring screen luminance is to use a spotmeter and manually measure the light level at many different points on the screen. After an adjustment is made, the process is repeated.

Computerized Projection System Analyzer

The combination of a specialized CCD camera and a small computer can be used to measure the luminance levels on the entire screen in real time. We at Ultra Stereo Labs. have been working with such a device for the past year. We believe that it will be an important factor in improving and expediting the on-screen measurement process. We call it the Projection System Analyzer.
A TV camera is placed in the center of the audience area and adjusted to view the entire screen. The camera output is connected to a small gray box in the projection booth which contains video processing circuits and a small computer. This is called the Analyzer and Interface unit. A laptop computer is used to control the measurements and to display the results.
The laptop display can show either the TV image of the movie screen as the camera sees it, or a graphical representation of the movie screen which displays the luminance values. The graphical representation is divided into a nine-by-five grid, showing the luminance readings for each of the 45 zones. This provides an immediate and continuous display of the light distribution across the entire movie screen.
Additionally, the background of each zone is shaded in accordance with the light value in that area. The shading emphasizes the pattern of light distribution. This gray scale emphasis or enhancement makes it easy to discern the variation in light across the screen. This becomes important when adjusting the X,Y and Z controls of a lamp-house. The technician or person adjusting the lamp-house watches the laptop display rather than the movie screen. Use of this instrument can cut lamp-house adjustment time from 5 or 10 minutes to 30 seconds or less.
The camera and analyzer instrument can also be used to measure the parameters of image steadiness, flicker and contrast.

Technical Discussion

A CCD camera is a natural light measuring device. The amplitude of the video output is linearly proportional to exposure. The video is sampled by an A/D converter and each frame of the video is stored in memory to allow for computer measurements. Commands from the laptop computer determine which measurements are to be made.

Luminance
For the luminance readings, the video level is measured at ten different places in each zone. The readings for each zone are averaged over a period of two and a half seconds and then the final value is placed in a table. After correction factors for camera gain and lens characteristics are applied, the luminance values for each zone are sent to the laptop for display.
The camera is normally positioned, and the zoom lens adjusted so that the camera view covers the movie screen and masking. The aiming and positioning of the camera is not critical, as long as the TV image includes the entire screen. A small viewfinder is mounted on the rear of the camera, along with a rocker switch for control of the zoom lens. An algorithm in software locates the exact edges of the movie screen in the camera view. All zone luminance measurements are made within the borders of the screen. The nine-by-five zone grid is aligned with the movie screen and inset by 5%, to prevent any ragged edges from affecting the measurements.
When viewing the "camera view" display of the laptop, you see the movie screen and an area around it that would normally cover the masking and curtains. In this mode, a spotmeter is available that follows the cursor and reads the luminance in a small area that corresponds to approximately one degree. This is useful in measuring the light manually, at any point on the screen or it's immediate surroundings. The spotmeter function is particularly useful when making measurements of ambient light, reflected light and lens flare. The gray scale enhancement is active in this display mode so that the screen luminance pattern may be seen.

Image Steadiness
The parameters of image steadiness can be measured with the camera and computer. For the measurement of weave, for example, the computer picks up a vertical line in the image and measures the time delay between the left raster edge and the vertical line. With weave, the time-position of that vertical line will vary. If the computer continually measures the time-position, then the peak-to-peak excursion can be determined. If we compare this value to the image width, then we can calculate the weave as a percentage of image width. We measure both the image width and the horizontal motion of the vertical line in terms of time instead of linear dimensions. We still have the proper ratio.
We can also perform an FFT algorithm on the time-position signal, and come up with a spectral display of the weave components showing their individual amplitude and frequency. This is very useful for analysis or troubleshooting of a projector.
The same process can be used to measure jump or jitter of the projected image. In that case, the position or timing of a horizontal line is measured with respect to the end of vertical blanking.

Contrast
Image quality is dependent upon the ratio of the high-light luminance to the darkest possible scene or area projected from film. The contrast ratio is limited by the "stray" light, such as ambient light from the aisle and wall lights, screen light reflected from the ceiling and walls and lens flare. The spotmeter function of the Projection System Analyzer can be used for measurements of these stray light sources.

Flicker
The Flicker display shows the frequency and amplitude of any flicker components below 12Hz. Sources of flicker, such as a bad lamp or power supply regulator can be more easily diagnosed with this capability.

Documentation
Software in the laptop computer can generate a report which contains all the pertinent data for each movie auditorium. This report shows the luminance for each zone of the screen as well as data from all other measurements made. The report can be printed out or retained on a floppy disk.

Accuracy
Several versions of the instrument have been built and tested during the past year. When calibrated with a spotmeter which is accurate within 2%, the accuracy has remained within +/- 5%. The CCD determines the majority of the accuracy and it is a very stable device within a reasonable temperature range.

Conclusion

The combination of a specialized CCD camera and a small computer can simplify and expedite on-screen measurements of projection system parameters. The instrument also provides an excellent means of documentation. This is important for comparative analysis and equipment monitoring and evaluation.
It seems certain that the Projection System Analyzer will be an important factor in improved measurements and better movie presentation.