1.  Field of Invention
The invention relates to an image processing apparatus and method thereof, and, in particular, to a PIP (Picture In Picture) processing apparatus and a processing method thereof. 
2.  Related Art
With the coming of video/audio ages, image displaying methods and image processing technology are developed rapidly, wherein the PIP (Picture In Picture) technology is the most widely used one for displaying images.  The PIP technology allows the user to watch a plurality of channels easily or view different sections of a film simultaneously. 
Illustrations will be made by taking the playing of television channels as an example, as shown in FIG.  1.  When the television PIP channels are being played, a first channel image 1 is displayed in a frame 2.  Next, the frame 2 is divided into a main image region 21 and a secondary image region 22 according to user's personal requirement or a default value.  At this time, a second channel image 3 is scaled down to overwrite and replace the secondary image region 22 of the first channel image 1.  Therefore, the user can watch the first channel image 1 and the second channel image 3 simultaneously.  As mentioned hereinabove, the conventional television has to be equipped with a PIP processing apparatus to process the image data for the subsequent playing of the PIP channels when the above-mentioned PIP playing procedure is performed. 
As shown in FIG.  2, a conventional PIP processing apparatus 4 is used in conjunction with a display 5.  The PIP processing apparatus 4 includes a first processing circuit 41, a second processing circuit 42 and an overwriting circuit 43.  The first processing circuit 41 receives and processes a main image 61 to generate a first to-be-displayed image 62.  The second processing circuit 42 receives and processes a secondary image 63 to generate a second to-be-displayed image 64.  At this time, when the display 5 wants to display the second channel image 3 in the secondary image region 22, as shown in FIG.  1, the overwriting circuit 43 receives the first to-be-displayed image 62 and the second to-be-displayed image 64, and overwrites and replaces the first to-be-displayed image 62 with the second to-be-displayed image 64 to output the second to-be-displayed image 64 to the display 5. 
However, as mentioned hereinabove, the conventional PIP processing apparatus 4 has to provide two processing circuits (including the first processing circuit 41 and the second processing circuit 42) for respectively processing the main image 61 and the secondary image 63 when the display 5 wants to display the second channel image 3 in the secondary image region 22 (see FIG.  1).  Thus, the conventional PIP processing apparatus 4 has larger product size and high product cost.  As shown in FIG.  1, when the second channel image 3 scaled down to replace the first channel image 1 is displayed in the secondary image region 22, the memory has to provide the memory bandwidths for the main image 61 and the secondary image 63 simultaneously for the purpose of the subsequent display of the secondary image region 22.  In other words, the conventional PIP processing apparatus 4 has to provide a redundant memory bandwidth to be shared with a partial main image 61 originally disposed in the secondary image region 22 (the secondary image region 22 is overwritten by the secondary image 63).