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In a conventional 3-tube elements camera, each of the elements is assigned to the RGB channels respectively. However, this method of one channel/element assignment is not effective if applied to the 3-chip CCD camera, yielding resolution problems, as well as signal aliasing problems, which are created by the use of solid-state chips as the image pickup elements.

Aliasing occurs in the CCD image sensor when the spatial freqency of image projected on the lage sensor in a given plane exceeds half the photo diode spacing in the image sensor on that plane.

To overcome these problems and to ovide the best balanced performance that can be achieved with current CCD chip pixel capacity 490(V) x 384(H) a dual green system was developed as the image pickup system for the SP-3 CCD camera.
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Designed as a broadcast-quality stand-alone ENG camera, the SP-3 (shown here with Sony Betacam 172" recorder) offers universal interface to all videotape formats: 1/2" Beta or VHS, 3/4" U-matic, as well as 1/4" VCRs. Solid-state operational characteristics feature accurate and permanent registration that is free from geometric distortion.

The dual green system attempts to approximate the performance of the human eye as it perceives color, taking into account the following: The light value ratio of green to red/blue is approximately 1.5:2; and in the NTSC color system, the bandwidth ratio of the luminance channel to the chrominance channels is about 4:1.

Consequently, in spite of the limitations inherent in having only 384 pixels for the horizontal picture elements (per CCD chip), with the dual green system it was possible to obtain a horizontal resolution of more than 500 TV lines.
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Combining the G signals (both) and splitting the RB (red-blue) signal - Refer to Figure 3 for a block diagram of the SP-3 camera. Because the horizontal shift registers of the CCD image sensors for Green1 and Green2 are driven by the two clock pulses (7.16MHz) with 180° phase shift, a 1H delayed signal and a 2H delayed signal for G1 and G2 can be obtained just through two 1H CCD-type delay lines without requiring a special delay line for phase matching respectively.

The non-delayed original signal, the 1H delayed signal and the 2H delayed signal for G1 and G2 are all combined, respectively, by three sample-and-hold (S.H) blocks, each consisting of two sample circuits and one hold circuit. Therefore, the data rate of the output signal from each of the sample-and-hold blocks is twice the rate of the output signal from each of the green CCD image sensors.

On the other hand, because the output signal from the red/blue CCD image sensor consists of alternating red and blue pictures at a rate of 7.16MHz, the red and blue signals can be easily split by using two sampling pulses (3.58MHz) with a 180° phase shift.
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The camera features a 2H-line type image sharpener by means of a high performance CCD delay line (DL) which has a 400% dynamic range and a 62dB signal-to-noise ratio.

The CCD delay line and the green image sensors are driven in parallel with the same clock signal to maintain proper timing between the signal coming from the green CCD image sensors and the delayed signal through the CCD delay lines.

The output of the three sets of sample-and-hold blocks (non-delayed, 1H delayed and 2H delayed video) is then fed to a comb filter and image sharpener to peak the high frequency components of the green channel signal and to generate edge component signals. In this system, the high frequency component of the green channel is also used to feed the red and blue channel signals to enhance their frequency content.

Output signals -The camera provides the following output signals:

• • Y, R- Y and B - Y signal for component VTR;
• • composite video signal with SP-1 AD adapter; and
• • direct RGB output signal with SP-2AD adapter.

An NTSC composite signal is also available as monitor for the built-in VTR system in camera/recorder combinations.
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The SP-3 camera incorporates auto and preset white balance, auto black balance, black stretch and auto iris.

The CCD color camera is designed to be used as a broadcast-quality ENG stand-alone camera, as well as in camera/recorder combined systems using on-board component VTRs for E v G applications.

Enhancing the versatility of the camera, available camera adapter attachments interface to external conventional portable VTRs, as well as to RGB image processing systems as a special application.

The SP-1AD camera adapter attachment is used to generate composite video signal output for conventional VTR recording. The SP-2AD camera adapter provides direct RGB output for use as a document camera or for image processing applications.

Because the SP-1AD camera adapter contains genlock and I/Q type encoder modules, it will generate a burst signal and a color frame pulse that will meet the RS-170A standard, as well as NTSC color signal requirements.

Remote-control functions are available for gain, pedestal, iris, SC and horizontal phase control, etc.

Compared with conventional 3-tube video cameras, the CCD camera offers several distinct advantages :
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• Solid-state operational characteristics feature accurate and permanent registration that is totally free from geometric distortion. In normal operation, no CCD chip ever requires replacement or adjustment.
• Disturbances such as electrical circuit deviations or the earth's magnetism that can affect registration and cause geometric distortion in conventional magnetically deflected cameras are totally ignored by the SP-3 camera.
• Furthermore, the CCD camera is completely free from burn-in. sticking and comet-tail that may occur in conventional pickup tube cameras when ligh intensity objects are viewed. Even if you were to shoot directly at he sun, no damage would be incurred o the elements.

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• As noted, under normal operation, the CCD chips of the SP-3 camera should never need replacement. If, for any reason, such replacement should ever become necessary, the camera should be returned to NEC for inspection and service. Although such service seems unlikely, BE explored the possibilities with NEC. The company said that individual chip replacement is possible. If the camera has been seriously mistreated, the entire optical block and all its CCDs can be replaced. In this worst-case situation, the cost would be approximately what you would expect for replacing the optics in a traditional tube-type camera. In any event, if your camera has been extensively damaged, you would probably want to replace it rather than service it.
• Aiming your expensive video camera at the sun, or at its reflection from a shiny surface, is not a recommended practice. However, according to NEC experts, such action, accidental or deliberate, does not have any apparent adverse effect on the immediate or long-term performance of the SP-3 camera. It is our understanding that NHK in Japan set up a CCD camera to tape an eclipse of the sun. A segment of the resulting tape was subsequently broadcast so that the public could view the event. BE is researching this work and will report details when they become available.

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• This article on the SP-3 CCD camera was provided courtesy of NEC America and excerpted from the NEC Synchronizer, Volume 2, No. 1, Winter 1984. A production version of the SP-3 camera was introduced at the SMPTE-1983/Los Angeles Convention, Oct. 30-Nov. 4, 1983. The camera is available now from NEC essentially from stock, for approximately $ 19.000 (without lens). For a quotation, contact the Broadcast Equipment Division from NEC America.

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