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How computer operate in order to grap & process an image file from a camera via fire wire card?

Posted on 2011-09-25
Last Modified: 2012-05-12
Basically would like to understand what would be the impact of processing time different between a 2MB image file & 6MB image file generated from each of 2 MP camera & 6MP camera towards a computer operates?
Question by:pgsystech
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LVL 48

Assisted Solution

dbrunton earned 50 total points
ID: 36596928
By processing time I presume you meant the time to copy from camera to computer.

It will take longer to copy the larger file.  And that is probably the easiest statement to make.

By how much depends on all sorts of factors.  You'd expect that it would be 3 times longer but that might not be accurate.  There is overhead in doing the copying such as creating the copied file and closing it once the copy has been done.  A large file will copy across faster than a bunch of smaller files that are the same size as the large file.  Less overhead.

Your best bet is to time the operation for each of the file sizes rather than trying to get an estimation.
LVL 69

Accepted Solution

Callandor earned 450 total points
ID: 36598625
To actually generate an image, the camera has to send each pixel to the computer where it is constructed into a picture.  The speed at which it can do this is usually represented by the frames per second it can run at.  This depends on the network bandwidth and traffic (I am assuming these are megapixel IP cameras), the camera's ability to send the information, and the processing power of the card on the receiving end which constructs the image.

The net impact is the 6MP camera will typically have a lower capture rate (frames per sec) than the 2MP camera, so moving objects will not appear as smooth, though they will have more detail.

Author Comment

ID: 36657398
Yes Callandor, you are right that the 6MP camera have lower Frame Rates of 5 FPS whereas 2MP camera is able to go for 15 FPS. Both are on fire wire interface (IEEE1394) cable towards a PCI base interface card . Is that possible to understand details of each data flow steps with info of transfer rates or bus speeds on a computer operates in Core 2 Duo 2.4Ghz for example ? Thanks!
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LVL 69

Assisted Solution

Callandor earned 450 total points
ID: 36709130
The cpu is somewhat important, but the really important limitation is the method of transfer - in this case, both cameras are using Firewire, so they are limited to 400Mbits/sec total bandwidth.  If your 6MP camera is limited to 5 fps and your 2MP camera is limited to 15 fps, the calculation is as follows:

6MP = 6,000,000 pixels x 8 bit/pixel color x 5 fps = 240Mbit/sec
2MP = 2,000,000 pixels x 8 bit/pixel color x 15 = 240Mbit/sec

So your camera limitations are in line with what is expected; a little less than the maximum theoretical bandwidth (allow for overhead).

Author Comment

ID: 36715898
I see. It means that the camera FPS specs definitely comply to its limitation and will apply other type of interface like cameralink or GigE on high end camera (higher MP with high FPS camera)? Right? In this case, if the bottleneck is not on the firewire interface,  what should I focus on the 6.4MB each image file in terms of processing & analysis time towards my Core 2 Duo 2.4Ghz CPU system? Another question is any possible the system know how to utilize my graphic card (GPU=700Mhz) to take up the image processing load? Appreciate for any advice here. Thanks!
LVL 69

Assisted Solution

Callandor earned 450 total points
ID: 36753815
If your 6MP camera had a gigabit port (I doubt it does), you could theoretically have 20 fps, a slight improvement over Firewire.  Unless you have a modern gpu that supports multiple stream processors and a language like CUDA, I don't think you can offload image processing to your graphics card.  A dedicated capture card such as a Geovision GV-600 or something similar will be the fastest way to capture images; I think software running on the cpu will get bogged down and be unable to keep up (unless you have a special program developed privately).

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