Cheetah Python Camera with USB3 Interface
–
User Manual
December 5, 2017
Page
65
of
78
Rev 1.0
C5180 Frame
Rates (fps)
USB3 (FPS)
Full Resolution
15
3840 x 2160
40
1920 x 1080
142
1280 x 720
323
Table 5: Frame Rates for Various AOIs.
5.4 Subsampling
5.4.1 Pixel Averaging
The principal objective of pixel averaging is to reduce the image resolution with better
final image quality than using a subsampling function. Pixel averaging reduces the output
resolution by averaging several pixels together and has the advantage of reducing aliasing
and noise, which increases the signal-to-noise ratio (SNR). Subsampling
—
as opposed to
averaging
—
has the advantage of increasing the output frame rate by reducing the
number of rows read out, but also introduces aliasing in the final image. Subsampling,
however, increases the output frame rate more than pixel averaging.
You cannot apply both averaging and subsampling decimation simultaneously. The
camera does not support Zero ROT when averaging is enabled. Color cameras do not
support pixel averaging.
The following graphic illustrates the concept of 4:1 averaging for a monochrome image
sensor. The values of pixels P1, P2, P3 and P4 are summed together and the result is
divided by 4 to achieve an average of the 4 adjacent pixels.
Figure 36: Monochrome pixel averaging.
The averaging feature is usable on the full resolution image or within any area of interest.
For example, if the area of interest is defined as quad full HD (3840 x 2160) and 4:1
averaging is selected, the output is 1080P (1920 x 1080)
5.4.2 Subsampling Decimation
Subsampling reduces the number of pixels output by reducing the output frame size, but
maintains the full field of view. Selecting an area of interest (AOI) maintains the AOI field
of view.
The C5180, C4181, and C4180 employ a “keep one pixel, skip one pixel” sequence. When
enabled in both x and y, every other pixel within a line is retained and every other line
within the image is retained.
