Image Processing Reference
In-Depth Information
configuration is essentially on the basis that every pixel has a proper level of response, many
combinations are required at various points, such as each color spectral response, color con-
figuration, algorithm for color, and luminance signal processing. Therefore, depending on the
color distribution of the objects, the effect does not work, or, adversely, it falls to a low level.
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The ratio of the pixel numbers of R, G, and B is 1:2:1 in the Bayer configuration; however,
there is an example of improvements in resolution and sensitivity by increasing the num-
ber of G in the ratio to 1:6:1 for camcorder applications.
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7.3 Time Information
The improvement of time information is essentially high time resolution.
7.3.1 Frame-Based Sensors
In the frame-based integration mode in which exposure is prosecuted with a predefined
periodicity and exposure period, which almost all image sensors employ, a higher time
resolution and a higher modulation transfer function (MTF) can be obtained using a
higher frame rate and a shorter exposure period, as mentioned in Section 6.3. To that end,
the task is to find how a higher frame rate (frames/s: fps) or a higher output pixel number
rate (pixels/s) can be realized. The expedients for frame-based sensors are as follows:
1. Parallel output by multiple channels
2. High-speed digital output by column-parallel analog-to-digital converter (ADC)
3. Burst-type sensor with the required number of built-in frame memories
7.3.1.1 Parallel Output-Type Sensor
In this method, because the pixel signal output is shared by parallel multiple output chan-
nels, the output frequency can be increased by the number of output channels, as shown in
the conceptual diagrams in Figure 7.8a and b, illustrating a 4-channel output CCD and an
H-access
circuit 5
H-access
circuit 6
H-access
circuit 7
H-access
circuit 8
HCCD 3
HCCD 4
Image area
Image area
H-access
circuit 1
H-access
circuit 2
H-access
circuit 3
H-access
circuit 4
HCCD 1
HCCD 2
(b)
(a)
FIGURE 7.8
Examples of parallel output sensors: (a) CCD; (b) CMOS sensor.
