Toshiba 3CCD

Toshiba's IK-HD1 is a very small 3CCD camera, which dimension size is 32.6x38.6x41mm and 65g in weight. 3CCD uses three CCD image sensor chips to record R,G,B separately, unlike common demosaic type camera that each pixel contains three color filters.

Color Separation
3CCD origins from color separation photograph which had developed for a long time and once had limited success in history. But color separation method is still regarded as high quality solution. This method has following advantages:

• Efficiency
  For each color,Bayer filter single chip would loss at least 2/3 photons in color filter. Color separation with prism does not loss any photon in each pixel, making it perform better in low light condition.
• Color accuracy
  Unlike Bayer type, color separation method does not need demosaicing algorithm in interpolating color information to fill the gap in spatial domain. Each chip receive a single color at full resolution, providing the best color accuracy available.
  
• Aliasing free
  Bayer type single chip would encounter the problem of Moire patterns that spatial sampling of color is sparse relative to spatial frequency of optical image.

Philips Prism
The basic type of Philips Prism consists of three prism segments with two dichromatic filter to split 3 channels. Each prism has designed angle to make reflection beam to reflect again by total internal reflection, minimizing the effect of polarization and correcting the orientation for each output image.
First, long-pass filter reflect the blue color and then short pass filter reflect red and let green pass straightly. To make total internal reflection, blue and red need air layer to support very low index,and so there is a air gap between first and second prism segment about 10 micron thickness.For simplifying the architecture, the three color must has the same optical path distance.

Toshiba has proprietary prism technology to miniature the size and much expertise in electronics and precision manufacturing.
Challenges

• Alignment
  -in mechanic: position, prism assembly...
  -in electronic:gain, gamma curve....
• Temperature control
  -Temperature will cause signal variation between different sensor chip, so it would be better to keep each chip at the same temperature.
• Shading correction
  -The view angle for each chip would be slightly different because of prism.
• Ghost reflection
• Lens choices
  -The option for adapted camera lens is restricted. Philips prism with designed angle can't accept larger incident angle and light far from axis, especially for peripheral of view.

Market
For high definition requirement, 3CCD has superior performance in color fidelity.

• Diagnose
• Scientific imaging
• Endoscope
• HD photograph
• Others like defense, surveillance.....