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Color Imaging

Image Enhancement, Color Separation, Color Correction

Color imaging systems benefit from the use of precision optical filters which control the spectral properties of light and color separation to exacting tolerances. In addition, system performance improves with the elimination of wavelengths outside the visible spectrum. Image capture is enhanced when the prime colors of light are precisely separated or trimmed before reaching the detector. Image reproduction, where colors are recombined, also benefits from the use of precision filters. The end result is that image quality improves when a system's optics deliver precise color separation, high color signal-to-noise, and a wide dynamic range.

Omega Optical designs and manufactures a variety of precision filters for application in color imaging systems, from image capture and detection through image projection and display.


Color Image Enhancement

SpectraPLUS is a patented triple bandpass, interference filter coating that enhances color and improves overall spectral performance. This filter benefits color imaging systems as well as applications where the eye is the detector. The coating allows transmission of the three bands of pure color—red, green, and blue—while blocking those intermediate wavelengths that distort the perception or recording of color. It also eliminates wavelengths in the ultraviolet and near infrared which are detrimental to an accurate color rendering and visual record. SpectraPLUS offers accurate hue, enhanced saturation, increased color signal-to-noise, and a resulting improved Modulation Transfer Function (MTF).

Omega® Optical manufactures two SpectraPLUS coating designs—one is optimized for digital imaging sensors (XB29) and one is optimized for the human eye and film (XB30). All filters are finished to the highest imaging quality standards and are available in stock and custom sizes.
SpectraPLUS is protected by U.S. patent #5,646,781.

For more information download the SpectraPlus Flyer  (pdf, 392kb)

Digital Imaging Applications

Overview

The SpectraPLUS XB29 filter is specifically designed for use with digital imaging systems and CCD-based cameras. These systems are sensitive to wavelengths beyond the visible which contribute no useful information for color imaging.

This version of SpectraPLUS blocks the crossover regions between blue/green and green/red centered at 490nm and 600nm respectively. To prevent IR saturation of silicon-based sensors, the coating provides a high degree of attenuation in the near infrared region, from 750nm to 1100nm. The XB29 also offers complete attenuation of ultraviolet A and B, and deep blue up to 430nm. These wavelengths may seriously impact apparent color and reduce image sharpness.

For more information download the SpectraPlus Digital Camera Flyer  (pdf, 448kb).

Applications

SpectraPLUS XB29 has application in the optical systems of video cameras, remote sensing cameras, digital cameras for still photography, machine vision systems, and CCTV cameras. It eliminates the need for a red blocking filter, typical of CCD cameras. The XB29 is also appropriate for use in any color reproduction process based on digital sensor technology. These applications include pre-press scanners in the commercial printing industry, and desktop scanners and color copiers in the office products industry. As with all interference filters, the coating is most efficient across the entire field of view when the transmitted light is at an angle of incidence no greater than 30.

  • Commercial Printing Industry
    • Pre-Press Scanners
  • Machine Vision Industry
    • Camera & Lens Systems
  • Office Products Industry
    • Desktop Scanners
    • Color Copiers
    • Digital Copiers
  • Photography-Video-Film Industries
    • Video Cameras & Lenses
    • Digital Cameras & Lenses
    • Photo Scanners
  • Remote Sensing Industry
    • Camera Systems

Eye & Film Applications

Overview

The SpectraPLUS XB30 filter is optimized for applications where the human eye or photographic film is the detector. Color imaging is enhanced with increased saturation, accurate hue, and improved contrast and resolution. This version of the SpectraPLUS filter has two stop band regions centered at 490nm and 580nm for blocking the prime color "crossover" wavelengths between blue/green and green/red in the visible spectrum. The XB30 offers high attenuation of ultraviolet A & B. It also attenuates the near infrared in a band centered at 725nm.

Applications

SpectraPLUS XB30 has numerous applications in the photography, film, and video industries including: video, motion picture, and slide projection; photography, film, and video lenses; and enlarger lenses. In lenses the coating can be applied to lens elements or used as a discreet filter, both at slightly increased exposure time or lens aperture. In the architectural and theatrical lighting industries the filter can be used as a fixture filter or as a coating on bulbs or reflectors. It also has use in medical and dental lighting (where color rendition is important). The coating improves "seeing" in ski goggles, sports eyewear, sunglasses, and sports optics especially in low light and flat light conditions. The filter is most effective in applications where the light is collimated, striking the filter at angles of incidence less than 30.

  • Sports Eyewear Industries
    • Sunglasses
    • Ski Goggles
    • Active Sports Glasses
  • Lighting Industry
    • Track Fixture Filter
    • Fiber Optic Filter
    • Bulb & Reflector Coating
    • Medical & Dental Lights
  • Photography-Video-Film Industries
    • Camera Lenses
    • Video, Film, & Slide Projectors
    • Color & B&W Film Printers
    • Enlarger Lenses
  • Sports Optics Industry
    • Binoculars & Spotting Scopes
    • Rifle Scopes

Technical Information

All sensors—human eye, film, and electro-optical—have limitations in how they "see" and record color. Their receptors significantly overlap, as do the wavelengths for the three prime colors of light: red, green, and blue. A photon of light from within this overlap region can leave an incorrect signal on the receptor so that a green photon, for example, can be perceived or recorded as blue or red.

SpectraPLUS blocks wavelengths between prime colors, as well as blocking UV and near IR.

The human eye has optimal peaks at which it sees the three prime colors. Wavelengths between those peaks are "interpreted" as being a certain color, demonstrating the subjectivity of human color perception. Similarly, all still and motion picture films have three emulsion layers designed to detect wavelengths of the three prime colors. Overlapping wavelengths contribute confusing information to the recording of the scene's color on film. Imaging sensors, such as CCDs, experience similar problems. These systems utilize prisms and filters to divide the spectrum into bands of color which then activate individual pixels in a large or distinct array. Wavelengths of overlap between the bands cause confusion as to whether a pixel should be red, green, or blue. In addition to these regions of "crossover confusion" between the prime colors, ultraviolet and infrared wavelengths contribute confusing spectral information in certain sensors. For the color image to be accurately recorded in sharpness, hue, and saturation, these wavelengths in the UV and IR must be attenuated as well.

SpectraPLUS alleviates color registration problems.

All optical imaging systems suffer from dispersive and resulting chromatic aberrations that limit the ability to record the color image of an object with precision. The ideal lens allows only a single wavelength of color to reach the sensor. Modern lenses use multiple optical glasses of different dispersion to permit sharp and accurate images at up to three wavelength bands. Lenses are designed to select the peaks of the three prime colors and focus them on a common image plane. As a result, wavelengths other than pure red, green, and blue are not well focused.


Color Separation Filters

Color imaging and measurement systems utilize color separation filters as well as prisms to differentiate the prime color wavelengths. Image capture systems divide light into red, green, and blue before reaching the detector. Image delivery systems recombine the red, green, and blue to form an image. In either case, system performance can be enhanced by carefully controlling the wavelengths and the areas of overlap. Systems which use prisms to control the spectrum can have enhanced performance using color separation filters.

Color filters have application in color imaging and reproduction systems such as analog and digital video cameras, digital still cameras, digital and video projectors, scanners, and copiers. They also have application in color measurement instruments such as colorimeters and radiometers.

For applications with demanding specifications Omega Optical offers High Purity Color Separation Filters and Sets with extremely high optical purity. These filters eliminate any overlapping wavelengths between colors.


Color Correction Filters

Omega Color Correcting (CC) filters are a replacement for the gels made for photographic or critical image transfer processes, as well as other applications requiring a modification in the intensity of one of the subtractive colors. Being an interference coating, it is possible to create any required value. Standard values typically include 5 CC, 10 CC, 20 CC, 30 CC, 40 CC and 50 CC, and are available as Cyan (C), Magenta (M), and Yellow (Y) and as Blue (B), Green (G), and Red (R). In every case the efficiency of the additive colors is > 90%, so little loss in exposure results from their use.

Unlike the plastic gels and absorbing glass filters typically used, our Color Correcting filters are produced using high efficiency, dielectric interference coatings. With the inherent efficiency of interference coatings, the tendency to solarize or discolor is eliminated. In addition, by using interference rather than absorption, these products can withstand temperature well in excess of 100C.


Color Temperature Filters

Omega Color Temperature (CT) filters are also available to replace all absorbing glass and plastic filters. These coatings are used to shift the black body temperature of a light source to higher or lower values. As a result of an efficient coating process, little of the desired light is lost, and the resulting increase in exposure is minimized. With these custom coatings it is possible to provide small shifts of as little as 10 Mired to as much as 300 Mired. This range of values allows the shifting of a candle light to that of an overcast sky.

Unlike the plastic gels and absorbing glass filters typically used, our Color Temperature filters are produced using high efficiency, dielectric interference coatings. With the inherent efficiency of interference coatings, the tendency to solarize or discolor is eliminated. In addition, by using interference rather than absorption, these products can withstand temperature well in excess of 100°C.