Hi Martin, Martin Rubli wrote: > Hey Pablo, > >> The YUV mode definitely leads to a huge amount of data in that case. >> (if 15 or 30 fps is desired). With a firewire camera at least the >> capture wouldn't be a problem (no copying involved, all data >> transfered via DMA) > > How is Firewire different from USB in this case?
All memory transfer is handled by DMA, leading to little cpu load. The cameras firewire cameras I use at work do not have any problems with streaming 3 uncompressed VGA grayscale images at 30 fps over one firewire bus. Denis McLaughlin reported that the capture is not always steady when he tries streaming of a similar amount of data using USB2.0 and 4 logitech fusion cameras at VGA and 15 fps (and he is using MJPEG, which results in dramatically less bandwidth, 70kB instead of 300kB per frame.). I don't know if this is a camera or a driver issue though. Since I need to combine the images into one single image/panorama afterwards, having synchronized cameras would be best, but I think if the capture frequency is the same for each camera and stays constant, it is hopefully possible to do once define the offset in frames for each camera (relative to one master camera) after the capture. >> MJPEG support is good news, but there is not information on the web >> for with resolution and framerates it is supported. >> All information from logitech is just marketing bubbles, no hard facts >> there, like which mode is available at what image size and frame rate. > > I work for Logitech, so feel free to bring on criticism ... :-) *g* Thanks a lot for the detailed information! Nice to see that detailed information is/will be available on the web soon. I have one more question: I heard that the Quickcam Fusion uses a rolling shutter (which means that the whole image is not captured at once, but in a row by row, or similar manner). Is can lead to artefacts for moving objects. I understand that this is not a problem for the typical webcam user, but for some applications (mostly for merging multiple images into a panorama or doing stereo analysis or similar) it is preferable to have a progressive scan camera (where the whole image is captured at once). Do you know if logitech manufactures webcams with progressive scan sensors? ciao Pablo _______________________________________________ Linux-uvc-devel mailing list [email protected] https://lists.berlios.de/mailman/listinfo/linux-uvc-devel
