APPENDIX D - CMOS SENSOR CHARACTERISTICS
The following occurrences that may appear in images are specific to CMOS (Complementary Metal Oxide
Semiconductor) image sensors. They do not indicate malfunctions.
White Flecks
Although the CMOS image sensors are produced with high-precision technologies, fine white flecks may be
generated on the screen in rare cases. These flecks are caused by natural and / or artificial radition, which causes
a “false exposure”on the image sensor. The shape of these spots may vary from dots to lines or other —sometimes
irregular— shapes. These spots occur in random locations of the image, occur only in a single frame and are more
visible in dark images. This is a principle issue of all image sensors and
is not a malfunction
.
The white flecks especially tend to be seen in the following cases:
• When operating at a high ambient temperature
• When you have raised the gain (sensitivity)
The white flecks may be reduced by turning the camera off, then on again.
Aliasing
When fine patterns, stripes, or lines are shot, they may appear jagged or flickering.
Aliasing
refers to the effect
that is produced when a signal is imperfectly reconstructed from the original signal. It occurs when a signal is not
sampled at a high enough frequency to create an accurate representation.
This effect is shown in the following example of a
sinusoidal function
:
In this example, the dots represent the sampled data and the curve represents the original signal. Because
there are not enough sampled data points, the resulting pattern produced by the sampled data is a poor
representation of the original.
Focal Plane
Owing to the characteristics of the pickup elements (CMOS image sensors) for reading video signals, subjects
that quickly move across the screen may appear slightly skewed (i.e., tilted to the left or right, depending on the
direction of camera or subject movement). Since a CMOS sensor typically captures one row at a time within
approximately 1/60th or 1/50th of a second (depending on the refresh rate), it may result in a “rolling shutter”
effect. In such cases, the image is skewed.
Flash Band
If you film a strobe or quick-flashing light, brightness may differ between the upper and lower halves of the picture.
See the Focal Plane explanation above for a clarification of this occurrence.
Flicker
If you are recording under lighting that is produced by discharge tubes (such as fluorescent, sodium or mercury-
vapor lamps), the screen may flicker, colors may vary, or horizontal stripes may appear distorted. In such cases, set
the anti-flicker setting to 'on'. Depending on lighting types, such occurrences may not be improved with the anti-
flicker setting.
It is recommended to set the shutter speed to 1/100s in areas of 50 Hz power supply frequency, and to
1/60s in areas of 60 Hz power supply frequency.
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Summary of Contents for CM70-IP
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