Capturing Images

With unicap, there are two different methods to make image data available to the application: system buffers and user buffers.

By using system buffers, the image buffers are allocated by the lowlevel driver. The application will register a callback which is called from the capture thread of the driver every time a new frame of image data is available.

System buffers are the most performant way to access video data. For devices capable of performing a DMA access to a system buffer, no video data gets copied by the CPU before it reaches the application. Note however that some devices ( like the DFG/1394 ) are not capable of a DMA transaction of a whole image buffer. For such a device, there is no perfomance gain when using system buffers.

user buffers are allocated and handled by the application. The application queues the buffers into an input queue in unicap and synchronously waits for the buffers to complete. For devices that are not capable of performing a DMA transaction to a user provided buffer, this method involves an additional memory copy operation for each frame which costs a bit CPU performance.