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ADVANCED GLOBAL SHUTTER SENSORS
The CMOS image sensors used in the Redwood camera series feature global shutter capability. Global shutter means all pixels across the sensor capture light during the same period of time. In contrast, sensors which use a rolling shutter technique will stagger the start of exposure throughout the rows of the image. This leads to motion artifacts in fast-moving scenes, as well as uneven frame illumination if bright flashes occur partway through the exposure period. At the pixel level, global shutter capability is implemented through in-pixel circuitry, however as pixel sizes are decreased to allow higher resolutions, too much in-pixel circuitry reduces the pixel’s sensitivity. The ON Semiconductor XGS 45000 sensor features an advanced design which minimizes in-pixel circuitry, providing top-quality high-resolution images of fast-moving objects without motion artifacts.
HIGH SPEED DIGITAL VIDEO OUTPUTS
CoaXPress is a standardized high-bandwidth digital video interface for transmission of video data over single or multiple coaxial cables. Developed as a next-generation standard for the machine vision industry, CoaXPress combines high-speed serial link technology and low-cost coaxial cables to form a bidirectional full-duplex communication link between video sources (ie. cameras) and video receivers (ie. frame grabbers or DVRs). With advancements in image sensor technology, a high-performance interface is needed to allow the full bandwidth of these sensors to be utilized. The throughput limits of existing video interfaces such as 1-10 GigE Vision, USB3 Vision, and even Camera Link are easily eclipsed by the bandwidth of sensors such as those used in the Redwood camera series. Additionally, system designers using cameras with these interfaces are faced with limitations regarding cable length, robustness, complexity, and cost. The Redwood 447X52 models feature four CoaXPress outputs, each capable of 12.5Gbps data rate for a combined 50Gbps total throughput from the camera.
MULTI-ROI READOUT, SUBSAMPLING AND BINNING FEATURES
Several image formatting and manipulation features are provided in the feature set of the Redwood camera series. For inspection applications, a single camera can be used to provide highly detailed images of a wide area, but if known regions of interest (ROI) within the field of view are the only portions needing to be inspected, the camera’s multiple-ROI readout feature can minimize the data needing to be transferred to the processing system. Up to 16 separate non-overlapping window areas can be created, and a composite image of those regions is transmitted rather than the entire sensor image. This can help to also increase the camera’s frame rate, as the sensor will skip rows above, between and below the defined ROIs. Other features allow for optimizing the camera’s output data rate in different ways. Subsampling (pixel skipping) allows the full field of view to be transmitted at a lower resolution, but at higher frame rates. Binning and Averaging (digital, off-sensor) allow for optimization of the sensitivity or signal-to-noise ratio of the delivered images.
HIGH DYNAMIC RANGE
The Redwood 447X52 offers several options for optimizing how much dynamic range of a scene can be captured in each image. A high dynamic range (HDR) dual gain exposure mode is available to extend the dynamic range capabilities of the camera. In normal exposure modes, operators must decide the exposure time to be applied to all pixels in the sensor for that frame period, as well as the gain applied to the pixel signals before the digital readout proceeds. In the case of high dynamic range scenes, this is often at the expense of either shadow or highlight details. With the dual gain HDR feature, the sensor outputs each pixel twice with a different analog gain applied (high and low). Using an in-camera image fusion technique, images with up to 6dB higher intra-frame dynamic range can be achieved. Compared to HDR techniques which combine multiple independent exposures, or interleaved HDR techniques with alternating rows/columns of a sensor having different exposure times, dual gain HDR techniques retain full spatial resolution and have no introduced motion artifacts. However, the maximum frame rate of the sensor is halved due to having twice the number of pixels output per frame.
HIGH RESOLUTION AND HIGH FRAME RATE
The Redwood™ series is a family of high-throughput industrial video cameras designed with some of the fastest high-resolution CMOS image sensors available today. The 447X52 models feature the ON Semiconductor XGS 45000, a Super 35 format 44.7MP global shutter sensor. At full 8192 x 5468 resolution, frame rates up to 52fps (8/10-bit output) or 47fps (12-bit output) can be achieved. The 3.2μm square pixels use low-noise global shutter technology for artifact-free motion imaging. Both monochrome and color camera models are available to suit a variety of applications in industrial and scientific imaging, wide area observation, as well as virtual reality and special effects.
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