CMOS Sensor Characteristics

The following visual phenomena may appear in images captured with CMOS (Complementary Metal Oxide Semiconductor) sensors. These are inherent to CMOS technology and do not indicate a malfunction.

White Flecks

Although CMOS sensors are manufactured with high-precision technologies, small white specks may occasionally appear on the screen. These are caused by natural or artificial radiation that results in a “false exposure” on the sensor. Their shape may vary—dots, lines, or irregular forms—and they occur randomly, typically appearing only in a single frame, most noticeably in dark scenes. This is a known limitation of all image sensors and is not a defect.

White flecks are more likely to occur under the following conditions:

  • High ambient temperature
  • Increased gain (sensitivity) settings

Turning the camera off and then back on may reduce the visibility of these flecks.

Aliasing

When shooting fine patterns, stripes, or lines, you may notice jagged edges or flickering. This is known as aliasing, which happens when a signal is not sampled at a high enough frequency to accurately reconstruct the original. The result is a distorted representation of the image.

This can be visualized using a sinusoidal function:

Aliasing Sinus Example

In the image, the dots represent sampled data, while the curve is the original waveform. Due to insufficient sampling points, the output appears distorted.

Focal Plane Distortion

Due to how CMOS sensors capture video—reading data line-by-line—objects moving rapidly across the screen may appear skewed. This “rolling shutter” effect results in diagonal tilting of the image, depending on the direction of movement (of the subject or camera). This distortion is most common when panning quickly or recording fast motion.

Flash Band

When filming a strobe or flashing light source, you may see brightness differences between the top and bottom of the image. This is also caused by the rolling shutter effect described above.

Flicker

Recording under lighting generated by discharge tubes—such as fluorescent, sodium, or mercury-vapor lamps—may produce flickering, color shifts, or horizontal banding.

To reduce this, enable the camera’s anti-flicker setting. In some cases, depending on the light source, this may not fully eliminate the issue.

Recommended shutter speeds:

  • 1/100 sec in regions with a 50 Hz power supply
  • 1/60 sec in regions with a 60 Hz power supply