Image Acquisitionand Proces

Image Processing 127
FIGURE 5.58 Using ReadImage and WriteImage.
FIGURE 5.59 Using ReadMovie.
Also, it might be necessary for the software to drop frames or to extend the time
frames are displayed in order to play the movie in real-time, hence the Play at full speed
button.
5.7.1.4 Writing Movies
Movie writing is similar to multiple sequential images writing (Figure 5.60). Currently,
only spatial compression is supported, as using a format with temporal
compression will trigger a new key frame for each frame. QT_MovieAddFrame.vi
adds an image to the created movie and the frame duration (expressed in the movie
time base ticks, not in seconds) is speciÞed. Once all of the required frames are
added, the movie is closed with QT_MovieClose.vi.
5.7.1.5 Video Grabbing (Figure 5.61)
Video grabbing was the Þrst and only function of the initial version of QTLib and
although the original version supported only one video input at a time, the current
version supports up to 32 devices in parallel (Figure 5.61). QTLib has been successfully
tested with USB, 1394 FireWire, serial and built-in digitizer boards. As
described above, QTLib relies on video digitizer drivers to interface with image
acquisition hardware and although most of them respect the QuickTime standard,
some do so only partially or not at all, so you should conÞrm your hardware will
support the standard fully before purchasing it. Under Windows, the original QTLib