huffd.c

很好的JPEG图象解码器,基于VC环境开发。

 ((-1) << 13) + 1, ((-1) << 14) + 1, ((-1) << 15) + 1};

#define HuffExtend(x,s) {					\
    if ((x) < extendTest[s]) {					\
	(x) += extendOffset[s];					\
    }								\
}

/*
 *--------------------------------------------------------------
 *
 * HuffDecoderInit --
 *
 *	Initialize for a Huffman-compressed scan.
 *	This is invoked after reading the SOS marker.
 *
 * Results:
 *	None
 *
 * Side effects:
 *	None.
 *
 *--------------------------------------------------------------
 */
void 
HuffDecoderInit (dcPtr)
    DecompressInfo *dcPtr;
{
    short ci;
    JpegComponentInfo *compptr;

    /*
     * Initialize static variables
     */
    bitsLeft = 0;

    for (ci = 0; ci < dcPtr->compsInScan; ci++) {
	compptr = dcPtr->curCompInfo[ci];
	/*
	 * Make sure requested tables are present
	 */
	if (dcPtr->dcHuffTblPtrs[compptr->dcTblNo] == NULL) { 
	    fprintf (stderr, "Error: Use of undefined Huffman table\n");
	    exit (1);
	}

	/*
	 * Compute derived values for Huffman tables.
	 * We may do this more than once for same table, but it's not a
	 * big deal
	 */
	FixHuffTbl (dcPtr->dcHuffTblPtrs[compptr->dcTblNo]);
    }

    /*
     * Initialize restart stuff
     */
    dcPtr->restartInRows = (dcPtr->restartInterval)/(dcPtr->imageWidth);
    dcPtr->restartRowsToGo = dcPtr->restartInRows;
    dcPtr->nextRestartNum = 0;
}

/*
 *--------------------------------------------------------------
 *
 * ProcessRestart --
 *
 *	Check for a restart marker & resynchronize decoder.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	BitStream is parsed, bit buffer is reset, etc.
 *
 *--------------------------------------------------------------
 */
static void 
ProcessRestart (dcPtr)
    DecompressInfo *dcPtr;
{
    int c, nbytes;
    short ci;

    /*
     * Throw away any unused bits remaining in bit buffer
     */
    nbytes = bitsLeft / 8;
    bitsLeft = 0;

    /*
     * Scan for next JPEG marker
     */
    do {
	do {			/* skip any non-FF bytes */
	    nbytes++;
	    c = GetJpegChar ();
	} while (c != 0xFF);
	do {			/* skip any duplicate FFs */
	    /*
	     * we don't increment nbytes here since extra FFs are legal
	     */
	    c = GetJpegChar ();
	} while (c == 0xFF);
    } while (c == 0);		/* repeat if it was a stuffed FF/00 */

    if (c != (RST0 + dcPtr->nextRestartNum)) {

	/*
	 * Uh-oh, the restart markers have been messed up too.
	 * Just bail out.
	 */
	fprintf (stderr, "Error: Corrupt JPEG data.  Exiting...\n");
	exit(-1);
    }

    /*
     * Update restart state
     */
    dcPtr->restartRowsToGo = dcPtr->restartInRows;
    dcPtr->nextRestartNum = (dcPtr->nextRestartNum + 1) & 7;
}

/*
 *--------------------------------------------------------------
 *
 * DecodeFirstRow --
 *
 *	Decode the first raster line of samples at the start of 
 *      the scan and at the beginning of each restart interval.
 *	This includes modifying the component value so the real
 *      value, not the difference is returned.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Bitstream is parsed.
 *
 *--------------------------------------------------------------
 */
void DecodeFirstRow(dcPtr,curRowBuf)
    DecompressInfo *dcPtr;
    MCU *curRowBuf;
{
    register short curComp,ci;
    register int s,col,compsInScan,numCOL;
    register JpegComponentInfo *compptr;
    int Pr,Pt,d;
    HuffmanTable *dctbl;

    Pr=dcPtr->dataPrecision;
    Pt=dcPtr->Pt;
    compsInScan=dcPtr->compsInScan;
    numCOL=dcPtr->imageWidth;

    /*
     * the start of the scan or at the beginning of restart interval.
     */
    for (curComp = 0; curComp < compsInScan; curComp++) {
        ci = dcPtr->MCUmembership[curComp];
        compptr = dcPtr->curCompInfo[ci];
        dctbl = dcPtr->dcHuffTblPtrs[compptr->dcTblNo];

        /*
         * Section F.2.2.1: decode the difference
         */
        HuffDecode (dctbl,s);
        if (s) {
           get_bits(s,d);
           HuffExtend(d,s);
           } else {
           d = 0;
        }

        /* 
         * Add the predictor to the difference.
         */
        curRowBuf[0][curComp]=d+(1<<(Pr-Pt-1));
    }

    /*
     * the rest of the first row
     */
    for (col=1; col<numCOL; col++) {
        for (curComp = 0; curComp < compsInScan; curComp++) {
            ci = dcPtr->MCUmembership[curComp];
            compptr = dcPtr->curCompInfo[ci];
            dctbl = dcPtr->dcHuffTblPtrs[compptr->dcTblNo];

            /*
             * Section F.2.2.1: decode the difference
             */
            HuffDecode (dctbl,s);
            if (s) {
               get_bits(s,d);
               HuffExtend(d,s);
               } else {
               d = 0;
            }

            /* 
             * Add the predictor to the difference.
             */
            curRowBuf[col][curComp]=d+curRowBuf[col-1][curComp];
        }
    }

    if (dcPtr->restartInRows) {
       (dcPtr->restartRowsToGo)--;
    }
}

/*
 *--------------------------------------------------------------
 *
 * DecodeImage --
 *
 *      Decode the input stream. This includes modifying
 *      the component value so the real value, not the
 *      difference is returned.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      Bitstream is parsed.
 *
 *--------------------------------------------------------------
 */
void
DecodeImage(dcPtr)
    DecompressInfo *dcPtr;
{
    register int s,d,col,row;
    register short curComp, ci;
    HuffmanTable *dctbl;
    JpegComponentInfo *compptr;
    int predictor;
    int numCOL,numROW,compsInScan;
    MCU *prevRowBuf,*curRowBuf;
    int imagewidth,Pt,psv;

    numCOL=imagewidth=dcPtr->imageWidth;
    numROW=dcPtr->imageHeight;
    compsInScan=dcPtr->compsInScan;
    Pt=dcPtr->Pt;
    psv=dcPtr->Ss;
    prevRowBuf=mcuROW2;
    curRowBuf=mcuROW1;

    /*
     * Decode the first row of image. Output the row and
     * turn this row into a previous row for later predictor
     * calculation.
     */  
    DecodeFirstRow(dcPtr,curRowBuf);
    PmPutRow(curRowBuf,compsInScan,numCOL,Pt);
    swap(MCU *,prevRowBuf,curRowBuf);

    for (row=1; row<numROW; row++) {

        /*
         * Account for restart interval, process restart marker if needed.
         */
        if (dcPtr->restartInRows) {
           if (dcPtr->restartRowsToGo == 0) {
              ProcessRestart (dcPtr);
            
              /*
               * Reset predictors at restart.
               */
              DecodeFirstRow(dcPtr,curRowBuf);
              PmPutRow(curRowBuf,compsInScan,numCOL,Pt);
              swap(MCU *,prevRowBuf,curRowBuf);
              continue;
           }
           dcPtr->restartRowsToGo--;
        }

        /*
         * The upper neighbors are predictors for the first column.
         */
        for (curComp = 0; curComp < compsInScan; curComp++) {
            ci = dcPtr->MCUmembership[curComp];
            compptr = dcPtr->curCompInfo[ci];
            dctbl = dcPtr->dcHuffTblPtrs[compptr->dcTblNo];

            /*
             * Section F.2.2.1: decode the difference
             */
            HuffDecode (dctbl,s);
            if (s) {
               get_bits(s,d);
               HuffExtend(d,s);
               } else {
               d = 0;
            }

            curRowBuf[0][curComp]=d+prevRowBuf[0][curComp];
        }

        /*
         * For the rest of the column on this row, predictor
         * calculations are base on PSV. 
         */
        for (col=1; col<numCOL; col++) {
            for (curComp = 0; curComp < compsInScan; curComp++) {
                ci = dcPtr->MCUmembership[curComp];
                compptr = dcPtr->curCompInfo[ci];
                dctbl = dcPtr->dcHuffTblPtrs[compptr->dcTblNo];

                /*
                 * Section F.2.2.1: decode the difference
                 */
                HuffDecode (dctbl,s);
                if (s) {
                   get_bits(s,d);
                   HuffExtend(d,s);
                   } else {
                   d = 0;
                }
                QuickPredict(col,curComp,curRowBuf,prevRowBuf,
                             psv,&predictor);

                curRowBuf[col][curComp]=d+predictor;
            }
        }
      PmPutRow(curRowBuf,compsInScan,numCOL,Pt);
      swap(MCU *,prevRowBuf,curRowBuf);
    }
}