Image Sensors
Another deciding factor in dome selection is the image sensor. Whether the sensor comes with an image processor will affect image quality, along with the sensor 's format, Chang said.
Resolution and frame rate are considerations in sensor selection. “Low-light performance is also important,” Corrall said. Global shutter on CMOS chips has better image results compared to rolling shutter.
However, CCD sensors still outperform CMOS ones in most low-light conditions. “For image sensors for fixed domes, good low-light performance requires CCDs,” Huang said. “But as CMOS improves, that will change.”
To differentiate, some vendors develop their own image sensors, while making themselves less vulnerable to sourcing fluctuations from component suppliers. “We provide image sensors for both CCD and CMOS,” said Iida Atsushi, PM of Security Solutions, Business and Professional Products for APAC, Sony Electronics. Pan-tilt mechanisms are also made in-house, saving sourcing time; on the other hand, they add to development cost.
The line between CCD and CMOS is almost always drawn at resolution, with analog and network domes delivering different results. “An analog image is interlaced, so if an analog dome is connected to an encoder, you only see about 400 TVLs,” said Caroline Kuan, Marketing Specialist at DynaColor.“IP domes are at least 600 TVLs, which make a difference in image quality.”
True network cameras use progressive scan, Fr?nnlid added.