In a complete machine vision systems, industrial camera is one of the key components , its essential function is to transform optical signals to orderly electrical signals.Choosing the right camera is a key step in machine vision system design,and the image acquisition has a great importance ,because the video signal can be converted to the digital format for computer use through the image acquisition!In the machine vision system, There are several aspects you need to pay attention to when choosing an industrial camera.
1：The Advantages and disadvantages of improving resolution
Although high resolution industrial camera helps to improve the precision, these more clear，more accurate image will reduce the speed of the camera, industrial digital camera image data transmission is composed of a series number standing for pixel values of the digital .A resolution of 200 x 100 camera has 20000 pixels, therefore, 20000 numerical value will be sent to the acquisition system.If the industrial camera work under the 25 MHZ rate of data amount, it transmits a value in every 40 ns,making a whole image takes about 0.00008 seconds, the equivalent of 1250 frames per second.
Using the same data rate of 25MHz , it takes 0.012288 seconds when collecting the whole image, or the equivalent of 81.4 frames per second。These are all the expectations value, the actual camera frame rate will be lower, because we have to add the exposure and the number of adjustment, but increase the camera resolution will to lead to a decline in the proportion of the frame rate of the industrial camera . Although various industrial camera output configuration will improve the camera resolution under the condition of without sacrificing the pixel, it also needs to increase the complexity and cost.
2：speed and exposure.
When choosing an industrial digital camera, the imaging speed of object must be fully considered.For example, suppose that during the capturing the pictures, object did not move in the exposure , simple and cheap industrial camera can be used.As for the imaging of stationary objects or slowly moving objects，area-array cameras are most suitable.Because the entire array -area must be one-time exposure, during exposure time ,any movement can lead to blurred images, however, motion blur can be controlled by reducing exposure time or using the flash light ; For fast moving objects, when the moving object using an array of industrial camera, the parameter of moving objects should be considered when choosing the exposure time for industrial camera, the smallest feature of the object with a pixel on the characterization is considered you need , that is namely the object resolution, In the acquisition of moving object image is the rules to exposure must occur in the amount of mobile objects collected one pixel within the time. If the objects you collect are at a speed of 1 cm/SEC in uniform moving , and resolution of the object is set to 1 pixel/mm, the maximum exposure time you need is 1/10 of a second. Because the object moves a distance exactly equal to one pixel in the camera sensor, when using maximum exposure time there will be blur in a certain amount. In this case, it generally will tend to set the exposure time faster than the maximum value ,such as 1/20 of a second, you can keep the object image in the mobile within half a pixel. If the same object moving at a speed of 1 micrometer/SEC, the object resolution is 1 pixel/micron obje, then a second needed for maximum exposure is 1/10000. The faster of the exposure setting depends on the camera, and whether you can give enough light to object to get a good picture or not.
3. Frame rate
Frame rate of industrial camera is the number of complete frames sent to acquisition system in a scheduled period by an industrial camera , it is often called that as the number of frames per second. For example, maximum frame of an industrial camera at resolution of 640 x 480 is 50 frames per second. Therefore, this industrial camera needs 20 milliseconds to send a frame after exposure. , some industrial camera is reading one image at present exposure while collecting the next image exposure. It must be considered at the read time and the way of the moving object imaging, and further considered interval between frames without the exposure.
4. Spectral response and sensitivity
Industrial digital cameras are equipped with electronic sensors of the sensitive light energy.
The wavelength of the light-sensitive light energy for the camera normally ranges from 400nm to 1000nm. In addition to that, wavelength less than 400 nm belongs to the ultraviolet spectrum，and higher than 1000 nm is included in infrared spectrum. If have the demand for a particular wavelength of imaging, you can choose specific industrial camera according to the specific wavelength!Filter is used to block the unexpected wavelengths of light, but it is required to know about how well industrial camera responses to wavelengths of light on demand.
5.Bit Depth
Industrial digital camera produce the digital data, or pixel value. To become digital value, this data will have a number of bits per pixel, which is called the pixel bit depth. This depth usually ranges from 8 to 16 bits. In monochrome industrial camera, bit depth define the numbers from dark to light gray level, the 0 stands for the completely dark here, and the 255 (8 bit depth) stands for the completely light . The values between 0 and 255 means gray shadow, and value near the zero means dark gray, value near the 255 is almost white. 10 bits data provide 1024 gray levels, 12 bits data provide a 4096 gray levels, each application should be carefully to determine the use of gray level, or use the coarse gray-scale.Machine vision system usually uses the 8 bit pixels, use the 10 or 12 bits bits means doubling the data, the data as another type of transmitting data. This will leads to reduction of the system in speed, because use the two types of pixel bits, not all of the bits are meaningful. The higher bit depth also increases the complexity of system integration, because higher bit depths need the more wider bandwidth， in the case that especially industrial cameras has the multiple outputs.
The above key factors determine the industrial camera image acquisition part in the machine vision system,it also have a great influence on the positioning of machine vision system as well as the following image analysis. JPLY suggests that if you want to make the right decisions on image acquisition, while allowing other hardware type selection and cost control , take full consideration of these factors according to you own needs!
