ABSTRACT
Transcoding of images and videos accomplishes the task of converting them from one format to another. For an image encoded and compressed in a format, the conversion may involve repackaging it into a different compression standard. Image resizing, discussed in the previous chapter, is also a transcoding operation. For a video, there could be various types of transcoding operations, such as transforming it into a different compression standard. Even within the same standard, alteration of its bit rate, frame rate, frame size, etc., are considered transcoding operations. Transcoding is required for different multimedia applications involving their presentation and communication over heterogeneous devices and networks. For example, the resolution of a display device may vary from 240×160 of a palmtop to as high as 3280×2048 of an advanced monitor for medical diagnostics. To adapt the display of an image or video of a given resolution, we require to bring it within the permissible display resolution of the device. In most applications, services available for display and communication of video and images are restricted by their adherence to a few selected standards. Hence, transcoding provides an interface for accommodating other representations, not supported by those services. Consider a scenario, in which images are saved in a server in the JPEG2000 format, as it is usually more efficient than the JPEG standard in storage requirement. However, even today, JPEG is the standard of image representation widely supported by various applications for the purpose of display and processing. Many of them may not support JPEG2000. In this case, we have to transcode a JPEG2000 image into a JPEG standard, before feeding it to such an application.
