Applying USB 3.0 Cameras for the Purpose of High-Speed Imaging

The Lt225 and Lt425 are the most recent products released by Lumenera that excel at providing high quality, high-speed imaging for a multitude of applications. This article offers a brief high level overview of a few technical specifications that typically go into the development of a high-speed imaging camera.

Need for Speed

The frame rate of a camera will determine the shortest time between two events that can be captured. Although single frame exposures can be achieved down to fractions of a millisecond using standard cameras, their frame rate limits the shortest time between events to be on the order of 16 to 33 milliseconds at full resolution.

A majority of the camera technology by Lumenera allows for sub-windowing of the image where a smaller portion of the frame is output resulting in higher frame rates. However, with the introduction of the Lt225 and its big brother the Lt445, high resolution and high-speed imaging is achievable. The Lt225 has a resolution of 2048 x 1024 and outputs 170fps. These high frame rates are achieved using an onboard memory buffer coupled with adaptive data flow management logic in a high-speed FPGA providing the reliable delivery of images with no lost frames in any environment.

USB 3.0 – Easy High Performance

USB 3.0 provides a high-speed data interface (even super speed), with the ease-of-use of a consumer oriented technology. No need for specialized frame grabbers, exotic cabling or tedious software installation. One advantage offered by USB 3.0 over the specialized machine vision bus technologies is so much easier to use. Also, the ubiquity of USB 3.0 ensures the standard has matured to a solid, reliable computer peripheral bus with access to a vast selection of devices.

Comparing Electronic Shutter: Global vs. Rolling

An electronic shutter regulates how light is exposed on an image sensor. There are two basic types of electronic shutter; Global and Rolling. In a sensor with a global shutter, all its pixels are exposed simultaneously for a period of time called the “exposure time”. In a sensor with a rolling shutter, the sensor’s pixels are exposed sequentially one by one left to right, row by row.

SKEW is described as the apparent leaning of moving objects in a scene. It appears when the motion is horizontal with respect to the camera field of view. This is shown in Figure 1.

Figure 1. Example of skew.

WOBBLE is the apparent shrinking or stretching of objects in a scene. Whereas, skew occurs when motion is horizontal to the field of view, wobble, occurs when the motion is vertical.

BANDING is the appearance of horizontal bands in the image that appear brighter than the rest of the image. The common cause is when using strobe lighting (e.g. a camera flash) during exposure.

CMOS Global Shutter

Until recently, CMOS sensors only offered rolling shutters, but technology has evolved in recent years making it possible to now implement quality global shutters. Not all global shutters are created equally. An important qualifier for global shutter performance is its efficiency, which measures how much parasitic light reaches the photosensitive area even when it should not.

Importance of Color

Color is opening doors to a world of new possibilities for an increasing number of machine vision applications. The camera in your system is the gateway to the color wonders of the world. A camera delivering accurate color is no small feat. At Lumenera the company designs and manufactures cameras so as to deliver accurate color, and ensures that a camera model will always deliver color in the same manner from unit to unit, no matter when it was manufactured.

Key Features of Lumenera Cameras are:

• Camera electronics are designed with proven, high performance components using the tightest tolerances, giving performance and repeatability to the design.
• Individual cameras are calibrated in the manufacturing process to compensate for individual variations.
• Final quality inspection by a team of trained specialists ensures excellent color performance.

Color Fidelity

The company’s success to color accuracy and repeatability is demonstrated by its strong presence in microscopy and life sciences applications. All color imaging applications rely on cameras that deliver accurate color in a repeatable manner even at a high frame rate.

In order to develop a camera, suitable for high-speed imaging, it is important to select a sensor with a global shutter that had suitable resolution and frame rate. In order to satisfy the image data rates, for ease of use and to keep the end user’s system costs to a minimum the company selected USB 3.0 as the data interface avoiding the need for complex software or a frame grabber. This was all combined with the company’s design expertise, proprietary processing algorithms and manufacturing capabilities resulting in the Lt series of cameras.

High Speed Imaging by Luminera

The Lt225 and Lt425 are high-speed cameras ideally suited for applications that include traffic monitoring, automatic license plate recognition (ALPR), high speed inspection and motion analysis and control. These cameras can be customized to suit Original Equipment Manufacturer (OEM) designs with specific form factor or enclosure requirements and are available in monochrome, color or enhanced near IR sensitivity models.

Scientific-grade versions are also available and suitable for life science applications such as digital pathology and slide scanning. Their high resolution and relative low noise is suitable for capturing enough detail to do all sorts of data analysis. Image capture can be synchronized using either a hardware or software trigger and is complemented by 128MB of onboard memory that is used for frame buffering to ensure full image delivery with no loss of data.

Table 1 shows the camera characteristics.

Table 1. Camera characteristics.

Figure 2. Color quantum efficiency curve.

Figure 3. Monochrome quantum efficiency curve.

The compact, light weight design of these cameras, which measure 40x40x53mm and the multitude of threaded mounting holes, ensure easy, flexible integration into tight spaces and enclosures.

The fully locking USB 3.0 connector provides a simple and secure single cable plug and play installation. For additional functionality, simplified I/O cabling can be connected to the locking Hirose connector to support external power input as well as 1 optically isolated output, input and 2 configurable I/Os.

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This information has been sourced, reviewed and adapted from materials provided by Lumenera Corporation.

For more information on this source, please visit Lumenera Corporation.