Circuit sharing of MPEG and JPEG on IDCT

Abstract

A device and a method of sharing IDCT are disclosed. Firstly, a data word and an identifier for representing which one of several formats are extracted from a received word. Then the data word is treated with IDCT to be a signed word afterward. Then the signed word is transformed into a formatted word between the values of a maximum value and a minimum value. The data word and identifier can be received by a word receiving means and treated with IDCT by an IDCT means to generate a signed word. The signed word is transformed into a formatted word for outputting via a word transforming means. Such that words with different formats can be treated with a sharing IDCT to save the redundant cost.

1 . A method of sharing IDCT (Inverse Discrete Cosine Transform), comprising: 
 receiving an input word which comprises a data word and an identifier, wherein said identifier represents the encoding method of said data word;    performing IDCT on said data word to generate a signed word;    generating a formatted word according to a maximum value, a sub-maximum value, a minimum value, and a sub-minimum value corresponding to the identifier respectively; and    output said formatted word.    
   
   
       2 . The method of sharing IDCT of  claim 1 , wherein said signed word is encoded via two's complement.  
   
   
       3 . The method of sharing IDCT of  claim 1 , wherein the most significant bit of said signed word represents negative when it is 1, otherwise represents positive when it is 0.  
   
   
       4 . The method of sharing IDCT of  claim 1 , wherein said identifier comprises at least one bit.  
   
   
       5 . The method of sharing IDCT of  claim 1 , wherein the encoding method of said signed word is chosen from one or combinations of the MPEG (Moving Picture Experts Group) and JPEG (Joint Photographic Experts Group) encoding method.  
   
   
       6 . The method of sharing IDCT of  claim 1 , wherein the formatted word is assigned a minimum value while said signed word is smaller than said minimum value.  
   
   
       7 . The method of sharing IDCT of  claim 6 , wherein if said signed word is smaller than said sub-minimum value and encoded in JPEG format, said formatted word is assigned said minimum value, smaller than said sub-minimum value.  
   
   
       8 . The method of sharing IDCT of  claim 2 , wherein said formatted word is assigned a maximum value while said signed word is larger than said maximum value.  
   
   
       9 . The method of sharing IDCT of  claim 8 , wherein if said signed word is larger than said sub-maximum value and encoded in JPEG format, said formatted word is assigned said maximum value, larger than said sub-maximum value.  
   
   
       10 . The method of sharing IDCT of  claim 2 , wherein if said signed word is neither smaller than said minimum value nor larger than said maximum value and encoded in MPEG format, said formatted word's value is assigned said signed word's value.  
   
   
       11 . The method of sharing IDCT of  claim 10 , wherein if said signed word is neither smaller than said sub-minimum value nor larger than said sub-maximum value and encoded in JPEG format, then said formatted word's value is assigned said signed word's value plus 128, wherein said sub-minimum value is larger than said minimum value and said sub-maximum value is smaller than said maximum value.  
   
   
       12 . The method of sharing IDCT of  claim 11 , wherein said minimum value, said sub-minimum value, said sub-maximum value, and said maximum value are −256, −128, 127, and 255 respectively.  
   
   
       13 . A device of sharing IDCT, comprising: 
 a word receiver for receiving an input word, wherein said input word comprises a data word and an identifier, and said identifier represents the encoding method of said input word where the encoding method has a plurality;    an IDCT device which performs IDCT on said data word and then generates a signed word; and    a word transforming device which transforms said signed word into a formatted word according to said identifier.    
   
   
       14 . The device of sharing IDCT of  claim 13 , wherein said identifier represents if said signed word is encoded in JPEG format or in MPEG format.  
   
   
       15 . The device of sharing IDCT of  claim 13 , wherein said formatted word comprises at least one function below: 
 said formatted word is assigned a minimum value while said signed word is smaller than said minimum value; and    said formatted word is assigned a maximum value while said is larger than said maximum value.    
   
   
       16 . The device of sharing IDCT of  claim 15 , wherein if said signed word is smaller than a sub-minimum value and encoded in JPEG format, said formatted word is assigned said sub-minimum value, larger than said minimum value.  
   
   
       17 . The device of sharing IDCT of  claim 15 , wherein if said signed word is larger than a sub-maximum and encoded in JPEG format, said formatted word is assigned said maximum value, larger than said sub-maximum value.  
   
   
       18 . The device of sharing IDCT of  claim 13 , wherein if said signed word is neither smaller than said minimum value nor larger than said maximum value and encoded in MPEG format, said formatted word's value is assigned said signed word's value.  
   
   
       19 . The device of sharing IDCT of  claim 18 , wherein if said signed word is neither smaller than a minimum value nor larger than a maximum value and encoded in JPEG format, then said formatted word's value is assigned said signed word's value plus 128, wherein said sub-minimum value is larger than said minimum value and said sub-maximum value is smaller than said maximum value.  
   
   
       20 . The device of sharing IDCT of  claim 19 , wherein said minimum value, said sub-minimum value, said sub-maximum value, and said maximum value are −256, −128, 127, 255 respectively.