1. Field of the Invention.

The invention relates to the light source used to read digital and analog information on photographic color dye film.

2. Description of the Prior Art.

In the prior art, during the late 1920 's, a process was developed whereby monophonic analog sound was recorded photographically on black and white motion picture film. In order to decode the sound, a tungsten lamp was focused through a lens and a scanning slit onto the film on which the sound was recorded and thereafter onto a photoelectric pickup device, where it was then processed into sound.

When color film was introduced in the 1950's, the process that had been previously used on black and white films to record an analog soundtrack would not work. The reason was that the color dyes used in making the film transmitted infrared light whereas the silver used on black and white film blocked infrared light. Since the incandescent sound light sources used to decode the soundtrack contained high amounts of infrared energy, it could not read the film modulation and created a great deal of noise. Therefore, it became necessary to add a black and white silver process in the soundtrack area to the color film.

Now, with the ever increasing public concern for the environment, film manufacturers are being pressured to omit the silver emulsion processing altogether and leave only the color dye processing on all

35mm prints. Color dyes block only visible light and are transparent to infrared light. Current tungsten incandescent sound lamps emit the majority of their energy in the infrared spectrum. Thus, they are not well suited for reproduction of silverless dye soundtracks. Further, the incandescent tungsten sound light sources have several problems when they are used to scan photographic color dye soundtracks.

One of the problems with incandescent sound light sources is that the average life of the incandescent light source is less than 1000 hours requiring frequent replacement. Second, the excessive heat in the incandescent sound light source distorts the shape of the filament and causes intensity variations over time which result in amplitude distortion in the sound playback. Third, the vibration components of

the projection machine can cause spurious microphonic problems in the sound system.

Thus, a sound light source is needed to read soundtracks on color dye films which omit the silver emulsion processing.

3. Benefits of the Invention

The present invention is characterised by a sound light source that overcomes the problems caused by the prior art incandescent light sources by combining leading edge LED technology with precision optics. The present invention is a replacement light source for the incandescent light source which illuminates the color dye film so the analog or alternative information encoded onto the color dye layers can be read. It combines long life, minimal heat dissipation and immunity from microphonic problems. Typical color dye film is composed of three dye layers -- a magenta dye layer, a cyan dye layer, and a yellow dye layer. Release prints can be made utilizing any or all of these dye layers. Any new projector sound light source must produce high intensity illumination in the visible range. Specifically, LED light sources can emit high levels of narrow spectral energy with very little infrared energy. Thus, if an LED process is selected that has a peak energy that coincides with the maximum density of a particular dye layer, an efficient, high quality system can be realized. Tests have shown that the a 660 nm GaAlAs ultrabright red coincides perfectly with the cyan dye density curves. (See curves in Figure 1.) The cyan color dye layer has the best resolution on color dye film.

In order simulate the sound light source of a tungsten filament, it is necessary to assemble a custom array of approximately ten to twelve individual LED die arranged in a straight line. The spacing between the LED die must be less than 15% of the size of the individual die in order to produce a band of light with minimal variation in intensity. The array is powered by a current regulating device such as a current regulator integrated circuit or resistor. Variations between LED die intensity is corrected through the use of compensation resistors.

In the present invention, in order to effectively match the array to existing projector optics, an immersion type lens is used in front of the LED die array. The lens redirects the wide LED output pattern into a small cone of light in order to allow it to efficiently enter existing projector optics.

Finally, the entire assembly is mounted in a standard sound lamp base to permit it to be easily installed in existing projection equipment.

FIG. 1 is a graph illustrating the typical spectral response of the dye layers on color print film and a GaAlAs 660 red LED array;

FIG. 2 is a block diagram of the preferred embodiment of the present invention; and

FIG. 3 is a block diagram of the present invention as it is mounted onto a base; and

FIG. 4 is a block diagram of the present invention as it is mounted in existing projection equipment.

Referring first to Figures 2, 3 and 4, the preferred embodiment of the present invention is characterised by fitting existing projectors with a sound light source 10 containing a narrow spectrum red LED array in order to be able to read the analog information on a film utilizing color dyes rather than silver emulsion. The present invention is characterised by a sound light source 10 that produces narrow spectrum high intensity illumination with very little infrared energy. Thus, the sound light source 10 has a peak energy that coincides with the maximum density of a color dye layer to create an efficient, high quality system. Tests have shown that the a 660 nm GaAlAs ultrabright red coincides perfectly with the cyan dye density curves. (See curves in Figure l.) In the preferred embodiment, the light source 10 peak energy coincides with the cyan color dye layer for the best modulation effect.

Referring more specifically to Figures 2 and 3, in order simulate the light source of a tungsten filament, it is necessary to assemble a custom array 12 of approximately ten to twelve individual LED die 14

arranged in a straight line. The spacing between the LED die 14 in the array 12 must be less than fifteen percent (15%) of the size of the individual die 14 to produce a band of light with minimal variation in intensity. The array is powered by a current regulating device 16 such as a current regulator integrated circuit (as shown) or by resistors. Any variations between the LED die 14 intensity are corrected through the use of compensation resistors 18. The intensity balancing resistors 18 and the current regulator 16 are mounted on circuit board 24 as shown in Figure 3. In the present invention, in order to effectively match the array to existing projector optics, an immersion type lens 20 is used. The lens 20 redirects the wide LED output pattern into a small cone of light to allow it to efficiently enter the existing projector optics, as shown in Figure 3. Referring more specifically to Figures 3 and 4, the entire solid state sound lamp assembly 10 is mounted in a standard lamp base 22 (a) and 22(b) to permit it to be easily installed in existing projection equipment. Thereafter, the invention is housed in housing 26 which contains an opening for the immersion lens 20. Thus, the present invention combines leading edge LED technology with precision optics so that it is now possible to replace the incandescent light source to illuminate color dye film so the analog or alternative information encoded onto the color dye layer can be read.

In the present invention, the LED die array will illuminate analog modulation on the color dye layers. Utilizing narrow spectrum LED's, the modulation effect will occur only by the cyan layer with minimal effect by the other dye layers. If the exposure on the other dye layers is off in any manner or if the other dye layers are not used, it will not effect the overall clarity of the analog sound. The same technique can be used with other dye layers provided the spectral peak coincides with the layer used such that multiple information on different dye layers can be simultaneously decoded. In addition, multiple color arrays can be incorporated in a single housing to allow playback of analog as well as alternative information. For example, digital information on the yellow or magenta dye layer may be simultaneously decoded by using additional arrays of different colors.

While particular embodiments and techniques of the present invention have been shown and illustrated herein, it will be understood that many changes, substitutions and modifications may be made by those persons skilled in the art. It will be appre-ciated from the above description of presently preferred embodiments and techniques that other configurations and techniques are possible and within the scope of the present invention. Thus, the present invention is not intended to be limited to the particular embodiments and techniques specifically discussed hereinabove.