How to determine which sensor I need?
The sensor is the most important part of a camera and defines most of its properties. Selecting a camera is mainly selecting its sensor. Each of the sensors available in the PicSight family has unique properties best suited for a particular application.
Here are common factors influencing sensor selection:
The Technology: Frame rate, electronic shutter, integration time, progressive scan, Global and Rolling shutter, windowing and partial scan. The task of a camera is to capture an image of an object for analysis. When the object is moving relative to the camera then the sensor should be fast enough to keep the image of the object within the same pixels to avoid blurr. The time that light accumulates on the sensor is commonly called integration time. For fast moving objects, this ability to freeze movement is further controlled with an electronic shutter controlling the exposure. It is available on all PicSight CCD sensors, P series (progressive scan), and on the CMOS G series (Global shutter). The CMOS R series (Rolling shutter) is usually not suited to capture moving objects because only one line integrates at a time, one after the others.
Another concern for moving objects is how often we need to acquire images. This parameter is the frame rate and is expressed in images or frames per second (fps). The standard value for a sensor is given for free running mode at full resolution. The actual frame rate is reduced if the sensor is in triggered or asynchronous reset mode, and may be increased by reducing the image size. CMOS sensors offer full flexibility for image reduction in both the X and Y directions (windowing), while CCD sensors can only suppress entire lines in the Y direction (partial scan).
For fast moving objects we suggest the following sensors:
-> G32M/B, this sensor has a high frame rate
-> P141M/B this sensor has superior sensitivity and Signal-to-noise ratio
For slow moving objects we suggest the following sensors:
-> R132M this sensor has Rolling shutter but has 1.3 Mpixel resolution, take 30fps and is cost effective
-> R312B this sensor has Rolling shutter but has 3Mpixel resolution, take 13fps and is cost effective
The Technology: Lens mount, sensor size, pixel size
The lens and the camera have to work hand in hand for best results. The obvious is to make sure the mount is the same. PicSight cameras are standard screw in C-mount so the lens should be also.
Another concern is to make sure that the sensor size is equal to or less than the projected image size of the lens, this to guarantee image quality in the entire image.
Finally, the resolution of the lens should be higher than or equal to the pixel size of the sensor. This is to avoid static blur in the image.
PicSight sensor size ranges from 1/4" up to 2/3", here are some typical sizes:
-> P34M/B, 1/4"; P33M/B, 1/3"; P32M/B, 1/2"; P141M/B, 2/3"
PicSight sensor pixel size ranges from 2.775um up to 9.9um, here are the extreme sizes:
-> R492B, 2.775um; P203B, 3.275um; P32M/B, 9.9um; G32M/B, 9.9um
The Technology: sensitivity, pixel size , anti-blooming, Spectral response, NIR
Lighting conditions have an impact on the selection of the sensor. When light is low or in the case of high speed applications, sensor sensitivity could be a key factor. However it cannot be standardized as it depends too much on the application specific conditions. For the same sensor generation, sensitivity is mostly influenced by pixel size, the larger the pixels, the more sensitive they are. It is interesting to note that sensors have different sensitivities depending of the wavelength of the light.
If the scene that the sensor captures contains very bright spots, such as the sun or a very strong reflection, blooming can appear in the image. It is the extension of the bright spot over the same lines or columns. If the bright spots must be contained, anti-blooming sensors must be selected.
Note that the PicSight cameras are standardly equipped with an Infra-Red filter to produce images looking more the way we see with our own eyes. This filter can be replaced by a clear float glass filter for full bandwidth or any custom filters for OEMs.
In case of reduced bandwidth imaging, NIR, laser, or other source, it is recommended to consult the sensor spectral response curves.
The Technology: pixel size, CCD, CMOS, resolution
When the images are the source data for inspection, there is a need for a very close relationship between the object being inspected and the image produced by the sensor. Noise is the number one problem. In a nutshell, noise is more likely to be reduced by choosing a CCD sensor rather than a CMOS sensor, by selecting the largest pixel size and by using a low value for gain. Note that all PicSight cameras use digital interfaces for better image quality and immunity from environmental conditions.
Processing of the image could also call for a minimum resolution. Vision software libraries usually specify how many pixels are required to make reliable measurements or inspections. You must have enough pixels in the image to meet your requirements. Too many pixels could be unnecessary and actually slow down procesing. PicSight cameras covers a wide variety of resolutions from VGA to 5M-pixels.
The Technology: CCD, CMOS, sensor size
Selecting a sensor can also be restricted by cost. CMOS and CCD sensors are pretty much similar in cost for the smaller sensor sizes whereas CMOS is substantially cheaper for larger sizes and resolution.
Color vs. Monochrome
The Technology: Bayer pattern
Sensors are available in monochrome or color. If the application is to look at monochrome parts then a monochrome sensor would be best suited. When a difference of color must be detected or measured then a color sensor would provide that extra information. All PicSight color cameras have a Bayer pattern sensor. It means that primary color filters are distributed across a monochrome sensor. To access the color information, an interpolation is required and can by done in-camera (PicSight RTF models), on frame grabbers (see PicPort frame grabbers) or performed on the host computer.
This link for more information about Bayer Pattern and color computation.
Examples of sensors:
P141M/B - 2/3" CCD, progressive scan, 1360x1024 pixels, 20fps, pixel size 6.45x6.45um
These sensors provide very good image quality for mega pixel resolution. They are used in demanding applications for industrial quality inspection or surveillance/traffic inspection.
G32M/B - 1/2" CMOS, global shutter, 659x494 pixels, 196 fps, pixel size 9.9x9.9um
These are fast and sensitive sensors to capture movement. They are used when high frame rate is required such as 10,000 parts per minute industrial gauging inspection, line profiling.
R312AB - 1/2" CMOS, rolling shutter, 2048x1536 pixels, 12fps, pixel size 3.2x3.2um This is a high resolution sensor with a very honorable frame rate. It is used to analyze scenes with human interactions such as Security, non-industrial monitori