Hi everyone, I am trying to use the Image Acquisition Toolbox to capture images from six webcams at the same time. The problem I am having is that only five actually work in MATLAB, even though all six will preview at the same time in other webcam programs. Is there a way to get MATLAB to use MJPEG instead of YUY2? The cameras do support MJPEG, which uses considerably less bandwidth, but it does not show up in matlab.
I am on windows 7 x64, with 12 gb of RAM. The CPU usage is below 30% with all cameras previewing. Are there any limitation I don't know about that would cause only 5 to work at a time? Maybe matlab is limiting memory or cpu usage, even though I have plenty? Any suggestions?
The most likely issue is that you are running into bandwidth limitations somewhere on your PC. My first thought was that it was a USB bandwidth limitation, but if you are able to acquire from five cameras simultaneously, I would guess that you are using at least two or three USB root controllers. This would mean that the culprit is likely not the USB bus, but the bridge between the USB controllers and the rest of the PC. If that is the case, there isn't too much that you can do. If you use an PCIe expansion card like this one (just the first example that I found) that might work, but that is really just a hunch.
We don't generally support JPEG compression from cameras since JPEG is a lossy compression method. This means that data is lost and the returned images are not true representations of the data that was captured by the camera. I can look into adding that in for a future version of the toolbox, but I'll have to think about it.
When all 6 are plugged in, do all 6 at least show up using IMAQHWINFO?
Is it always the same camera that is not accessible and if so, is this camera accessible from MATLAB when it is the only camera plugged in?
Here is my case, may be it helps the community ;).
Matlab image engine is not able to transfer the acquired video data (nearly 1.4 GBs for my case) directly to HDD during the capture, even if you use SSDs with enough bandwidth (source: Matlab Support). So, if you want to capture frame synchronized videos you need let whole data flow to RAM during the capture. Here is important to check the specs of your motherboard, chipset, USB host controllers etc. in order to avoid a bottleneck (check chipset diagrams). I'm using in my case 3 extra USB host controllers (<http://www.delock.de/produkte/G_89325/merkmale.html>) and two host controllers on the motherboard (bandwidth limited!). And the most important thing is to use the Microsoft USB Webcam driver, not the driver of the webcam! My experience is, you are not able to control the frame rate and capture synchronized through imaq when you don' t use Microsoft drivers. Below you can find an image, which shows the trigger times for 16 webcams.