Consider a typical inspection system (Fig. 1) consisting of an area camera inspecting an object with 4 holes near each corner. The inspection system exists to confirm the size and relative location of each hole.
The traditional CCD camera reads out the entire field of view with a resulting transmission bandwidth of 720 MPix/sec
Equation 1: Transmission BW (bandwidth) = Ymax * Xmax * bytes/pixel * Frame Rate.
Now consider a CMOS camera that is able to read only the rows of interest. In this case the transmission BW is 96 MPix/sec
Equation 2: Transmission BW = Number(Unique Y rows) * Xmax* bytes/pixel* Frame Rate.
We see that the improvement in Transmission BW is the ratio of Equation 1 to 2 and is 7.5 times
Equation 3: Transmission BW Improvement = Eq. 1/Eq. 2 = Ymax/Number(unique Y rows).
This improvement can be used to increase the system frame rate, improving productivity, or can be used to lower transmission BW and processing speed, resulting in lower costs.
Now consider a further reduction in costs by transmitting only the horizontal portion of interest. This gives a further cost reduction of 10x resulting in 9.6 MPixel/sec total BW.
Equation 4: = Xmax/(Sum(ROI widths accross the row)
In real systems, the objects move within the field of view and it is necessary to adjust the region of interest (ROI) locations for optimal performance. The application software is able to determine the ROI when the movement is slow and updates the camera as needed. If the object moves frame by frame, it is beneficial for the camera hardware, or frame grabber hardware to determine the ROI locations and communicate them to the rest of the system.
CLHS is releasing Revision 2 of its specification in support of multiple ROI. The committee hasn’t finalized the capability of multiple ROI but our goals include:
- up to 255 ROI, each of arbitrary size and location
- frame by frame control and synchronization from the application, the FG, or the camera
- control of frame pixel depth, pixel type, decimation factors, and other image parameters.
I would like to hear from you if your system can benefit from multiple ROIs, how quickly they need to change, and what camera parameters should be considered for frame by frame control and feedback to the host so that the CLHS specification upgrade provides the flexibility you need. Please contact me at firstname.lastname@example.org and I’ll share your requirements with the CLHS committee.