Digital Video Cameras: How the DV Format Works
DV digital video cameras have revolutionized the process of video capture and video editing. Previously, video cameras could store on tape, with video frames in formats like VHS and Hi8 which were analog formats. The DV format stores compressed frames at a speed of 25MB every second, and the technology is also known as Motion JPEG.
Analog and DV
The initial process of capturing a video is same in Analog and DV cameras. That is, they both use a lens for focusing on the image, and the sensor or CCD converts the image into electronic signals. The main difference between the two lies in the storing process. The DV camera will convert the signals into a compressed digital file format. This compression offers various advantages in storing superior quality images and also no loss of quality during copying. The superior quality of a DV format is because of storing the signal at a resolution of about 500 lines, whereas the analog formats are able to achieve 240 lines resolution.
Working of the DV Format
DV format uses a compression structure which is intraframe. This means the coding is done per individual frame independently. The compression is a combination of lossy and lossless techniques performed on the basis of the data of the current frame only. The compression is done per frame basis and not related to other frames.
In DV format, you have various options for audio. Among the various options, you have 16 bit or 32 bit stereo or CD quality audio in PCM. DV offers good synchronization of the audio with the video and less of drift over time.
Although the DV format is the same, there are two different methods employed in capturing the video by digital video cameras. Certain digital video cameras use the Interlaced scan format, while others use the Progressive scan for capturing video.
Cameras using the Interlaced scan format will capture the image in alternating line sets. One set of lines will be even numbered while the other set has the odd numbered lines. Each set of lines is called a field and when the two sequential fields are paired, the result is a frame. Due to this technique, this capture format has a higher frame rate per second giving the picture quality excessive realism.
Progressive scan methods used in video cameras will record identical fields and the resultant frame will be distinct. This method of screen capture is mostly preferred as the frame rate per second is around 25, which gives more realistic motion capture. You will find strobing effects like blurring of the object when seen in fast motion. Video cameras using the progressive scan method are usually costlier than the ones using the interlaced format of capture.
Advantages of DV
The DV format offers many advantages over analog. The chief one is that the quality of the video does not degrade even with repeated copying. Thus, digital footage will have almost an infinite life. The next major advantage of DV is the ease with which it can be transferred to a computer and edited with various sophisticated software available in the market today.