Monday, October 11, 2010

Why do progressive scan cameras help maximize image clarity?

Capturing moving objects is critically important to surveillance applications – for example, getting detailed images of vehicles moving or people running. There are two techniques used to render video: interlaced scanning and progressive scanning – and there is a noticeable difference in quality when it comes to capturing those moving objects!

Interlaced scanning technology was originally created to transfer analog video from the signal source (e.g., camera) to a CRT-based monitor. To create a complete picture, 480 active scan lines are required. The interlace camera divides the one image of 480 scan line image into two groups of 240 scan lines (Fields). One field with the odd and one with the even numbered scan lines, and then alternately sends them at 30 times per second. This delay produces distortion – such as flickering, and when there is motion in the picture motion blur, and “zipper” effect can be seen. While interlaced scanning has worked fine for basic TV, VHS, and analog video cameras, progressive scanning helps to maximize image clarity when moving objects are present.

A progressive scan camera captures the 480 scan line image all at one time. Then quickly sends the picture content line by line in a “progressive” manner. This method of image processing keeps the capture and sending of the complete image together (no field one/field two) thus producing clearer video with sharper motion details and virtually no distortion, zippering, or flickering.

Bosch’s IP cameras now offer all the benefits of progressive scanning – providing much better detail for scenes with moving objects – while maintaining manageable bitrates through the use of H.264 main profile compression technology.

However, it is not possible to capture then send progressive scan video and an interlaced video stream at the same time. But, we understand the importance and ease of camera focus and setup via a standard analog monitor. So, the Bosch engineering team has come up with a unique “service mode” feature. This mode activates the analog output and triggers the camera’s scanning system to move into interlacing mode. Now, the camera can be viewed on a standard analog test monitor. During this time, it is not possible to stream progressive scan video over IP.

When installation is complete and the “service mode” is turned off, the progressive scanning becomes active, and the Bosch IP camera starts to send high quality video images into the IP network.