NCJ Number
36143
Date Published
1976
Length
50 pages
Annotation
THIS REPORT DESCRIBES A LIGHT SOURCE DESIGNED FOR MEASURING THE SPECTRAL RESPONSIVITY OF MONOCHROME TELEVISION CAMERAS TO BE USED IN RECORDING COURT PROCEEDINGS.
Abstract
IT DESCRIBES A SIMPLE PROCEDURE FOR MAKING SUCH MEASUREMENTS. THE LIGHT FROM A QUARTZ-HALOGEN LAMP IS DIFFUSED AND PASSES THROUGH AN ARRAY OF TWELVE INTERFERENCE FILTERS, OF 50 NM BANDPASS EACH, WITH PEAK WAVELENGTHS AT ABOUT 50 NM INTERVALS FROM 400 TO 950 NM. THE SPECTRAL TRANSMITTANCE OF THE DIFFUSER, AND OF EACH INTERFERENCE FILTER-DIFFUSER COMBINATION, WAS MEASURED, AND FACTORS ARE SUPPLIED TO COMPUTE THE RADIANCE OF THE LIGHT TRANSMITTED BY EACH FILTER FROM THE MEASURED LUMINANCE OF THE DIFFUSER. A STEP WEDGE, WITH 21 STEPS, IN WHICH THE RATIO OF THE TRANSMITTANCE OF ADJACENT STEPS IS ABOUT 2, IS LOCATED BELOW THE ARRAY OF INTERFERENCE FILTERS. THE GAMA OF THE TELEVISION CAMERA IS EVALUATED BY USE OF THE STEP WEDGE. THE VOLTAGE OF THE VIDEO SIGNAL PRODUCED WHEN THE IMAGE OF EACH FILTER IMPINGES ON THE FACE OF THE CAMERA TUBE IS MEASURED, AND DIVIDED BY THE RADIANCE OF THE FILTER RAISED TO THE GAMMA POWER, TO OBTAIN THE RELATIVE SPECTRAL RESPONSIVITY OF THE CAMERA AT THE PEAK WAVELENGTH OF THE FILTER. THE RESULTS ARE NORMALIZED BY DIVIDING EACH VALUE BY THE MAXIMUM VALUE OBTAINED, AND THE QUOTIENTS ARE PLOTTED AS A FUNCTION OF WAVELENGTH TO PRODUCE THE SPECTRAL RESPONSIVITY CURVE OF THE CAMERA. THE TEST METHOD WHICH WAS DEVELOPED IS SUITABLE FOR THE EVALUATION OF THE SPECTRAL RESPONSIVITY OF MONOCHROME TELEVISION CAMERAS. IT IS SIMPLE TO APPLY, AND YIELDS DATA WHICH IS SUFFICIENTLY ACCURATE TO PROVIDE USEFUL INFORMATION CONCERNING THE IMAGE QUALITY OF THE CAMERA. USING THIS METHOD, IT IS POSSIBLE TO EVALUATE THE SPECTRAL RESPONSIVITY OF A CAMERA IN ABOUT THREE HOURS. (AUTHOR ABSTRACT (SNI ABSTRACT)