/******************************************************************************

 * tif_overview.c,v 1.9 2005/05/25 09:03:16 dron Exp

 *

 * Project:  TIFF Overview Builder

 * Purpose:  Library function for building overviews in a TIFF file.

 * Author:   Frank Warmerdam, warmerdam@pobox.com

 *

 * Notes:

 *  o Currently only images with bits_per_sample of a multiple of eight

 *    will work.

 *

 *  o The downsampler currently just takes the top left pixel from the

 *    source rectangle.  Eventually sampling options of averaging, mode, and

 *    ``center pixel'' should be offered.

 *

 *  o The code will attempt to use the same kind of compression,

 *    photometric interpretation, and organization as the source image, but

 *    it doesn't copy geotiff tags to the reduced resolution images.

 *

 *  o Reduced resolution overviews for multi-sample files will currently

 *    always be generated as PLANARCONFIG_SEPARATE.  This could be fixed

 *    reasonable easily if needed to improve compatibility with other

 *    packages.  Many don't properly support PLANARCONFIG_SEPARATE. 

 * 

 ******************************************************************************

 * Copyright (c) 1999, Frank Warmerdam

 *

 * Permission is hereby granted, free of charge, to any person obtaining a

 * copy of this software and associated documentation files (the "Software"),

 * to deal in the Software without restriction, including without limitation

 * the rights to use, copy, modify, merge, publish, distribute, sublicense,

 * and/or sell copies of the Software, and to permit persons to whom the

 * Software is furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included

 * in all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS

 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL

 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING

 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER

 * DEALINGS IN THE SOFTWARE.

 ******************************************************************************

 */

/* TODO: update notes in header above */

#include <stdio.h></stdio.h>

#include <assert.h></assert.h>

#include <stdlib.h></stdlib.h>

#include <string.h></string.h>

#include "tiffio.h"

#include "tif_ovrcache.h"

#ifndef FALSE

#  define FALSE 0

#  define TRUE 1

#endif

#ifndef MAX

#  define MIN(a,b)      ((a

#  define MAX(a,b)      ((a>b) ? a : b)

#endif

void TIFFBuildOverviews( TIFF *, int, int *, int, const char *,

                         int (*)(double,void*), void * );

/************************************************************************/

/*                         TIFF_WriteOverview()                         */

/*                                                                      */

/*      Create a new directory, without any image data for an overview. */

/*      Returns offset of newly created overview directory, but the     */

/*      current directory is reset to be the one in used when this      */

/*      function is called.                                             */

/************************************************************************/

uint32 TIFF_WriteOverview( TIFF *hTIFF, uint32 nXSize, uint32 nYSize,

                           int nBitsPerPixel, int nPlanarConfig, int nSamples, 

                           int nBlockXSize, int nBlockYSize,

                           int bTiled, int nCompressFlag, int nPhotometric,

                           int nSampleFormat,

                           unsigned short *panRed,

                           unsigned short *panGreen,

                           unsigned short *panBlue,

                           int bUseSubIFDs,

                           int nHorSubsampling, int nVerSubsampling )

{

    toff_t	nBaseDirOffset;

    toff_t	nOffset;

    (void) bUseSubIFDs;

    nBaseDirOffset = TIFFCurrentDirOffset( hTIFF );

    TIFFCreateDirectory( hTIFF );

/* -------------------------------------------------------------------- */

/*      Setup TIFF fields.                                              */

/* -------------------------------------------------------------------- */

    TIFFSetField( hTIFF, TIFFTAG_IMAGEWIDTH, nXSize );

    TIFFSetField( hTIFF, TIFFTAG_IMAGELENGTH, nYSize );

    if( nSamples == 1 )

        TIFFSetField( hTIFF, TIFFTAG_PLANARCONFIG, PLANARCONFIG_CONTIG );

    else

        TIFFSetField( hTIFF, TIFFTAG_PLANARCONFIG, nPlanarConfig );

    TIFFSetField( hTIFF, TIFFTAG_BITSPERSAMPLE, nBitsPerPixel );

    TIFFSetField( hTIFF, TIFFTAG_SAMPLESPERPIXEL, nSamples );

    TIFFSetField( hTIFF, TIFFTAG_COMPRESSION, nCompressFlag );

    TIFFSetField( hTIFF, TIFFTAG_PHOTOMETRIC, nPhotometric );

    TIFFSetField( hTIFF, TIFFTAG_SAMPLEFORMAT, nSampleFormat );

    if( bTiled )

    {

        TIFFSetField( hTIFF, TIFFTAG_TILEWIDTH, nBlockXSize );

        TIFFSetField( hTIFF, TIFFTAG_TILELENGTH, nBlockYSize );

    }

    else

        TIFFSetField( hTIFF, TIFFTAG_ROWSPERSTRIP, nBlockYSize );

    TIFFSetField( hTIFF, TIFFTAG_SUBFILETYPE, FILETYPE_REDUCEDIMAGE );

    if( nPhotometric == PHOTOMETRIC_YCBCR || nPhotometric == PHOTOMETRIC_ITULAB )

    {

        TIFFSetField( hTIFF, TIFFTAG_YCBCRSUBSAMPLING, nHorSubsampling, nVerSubsampling);

        /* TODO: also write YCbCrPositioning and YCbCrCoefficients tag identical to source IFD */

    }

    /* TODO: add command-line parameter for selecting jpeg compression quality

     * that gets ignored when compression isn't jpeg */

/* -------------------------------------------------------------------- */

/*	Write color table if one is present.				*/

/* -------------------------------------------------------------------- */

    if( panRed != NULL )

    {

        TIFFSetField( hTIFF, TIFFTAG_COLORMAP, panRed, panGreen, panBlue );

    }

/* -------------------------------------------------------------------- */

/*      Write directory, and return byte offset.                        */

/* -------------------------------------------------------------------- */

    if( TIFFWriteCheck( hTIFF, bTiled, "TIFFBuildOverviews" ) == 0 )

        return 0;

    TIFFWriteDirectory( hTIFF );

    TIFFSetDirectory( hTIFF, (tdir_t) (TIFFNumberOfDirectories(hTIFF)-1) );

    nOffset = TIFFCurrentDirOffset( hTIFF );

    TIFFSetSubDirectory( hTIFF, nBaseDirOffset );

    return nOffset;

}

/************************************************************************/

/*                       TIFF_GetSourceSamples()                        */

/************************************************************************/

static void 

TIFF_GetSourceSamples( double * padfSamples, unsigned char *pabySrc, 

                       int nPixelBytes, int nSampleFormat, 

                       uint32 nXSize, uint32 nYSize, 

                       int nPixelOffset, int nLineOffset )

{

    uint32  iXOff, iYOff;

    int     iSample;

    iSample = 0;

    for( iYOff = 0; iYOff < nYSize; iYOff++ )

    {

        for( iXOff = 0; iXOff < nXSize; iXOff++ )

        {

            unsigned char *pabyData;

            pabyData = pabySrc + iYOff * nLineOffset + iXOff * nPixelOffset;

            if( nSampleFormat == SAMPLEFORMAT_UINT && nPixelBytes == 1 )

            {

                padfSamples[iSample++] = *pabyData;

            }

            else if( nSampleFormat == SAMPLEFORMAT_UINT && nPixelBytes == 2 )

            {

                padfSamples[iSample++] = ((uint16 *) pabyData)[0];

            }

            else if( nSampleFormat == SAMPLEFORMAT_UINT && nPixelBytes == 4 )

            {

                padfSamples[iSample++] = ((uint32 *) pabyData)[0];

            }

            else if( nSampleFormat == SAMPLEFORMAT_INT && nPixelBytes == 2 )

            {

                padfSamples[iSample++] = ((int16 *) pabyData)[0];

            }

            else if( nSampleFormat == SAMPLEFORMAT_INT && nPixelBytes == 32 )

            {

                padfSamples[iSample++] = ((int32 *) pabyData)[0];

            }

            else if( nSampleFormat == SAMPLEFORMAT_IEEEFP && nPixelBytes == 4 )

            {

                padfSamples[iSample++] = ((float *) pabyData)[0];

            }

            else if( nSampleFormat == SAMPLEFORMAT_IEEEFP && nPixelBytes == 8 )

            {

                padfSamples[iSample++] = ((double *) pabyData)[0];

            }

        }

    }

} 

/************************************************************************/

/*                           TIFF_SetSample()                           */

/************************************************************************/

static void 

TIFF_SetSample( unsigned char * pabyData, int nPixelBytes, int nSampleFormat, 

                double dfValue )

{

    if( nSampleFormat == SAMPLEFORMAT_UINT && nPixelBytes == 1 )

    {

        *pabyData = (unsigned char) MAX(0,MIN(255,dfValue));

    }

    else if( nSampleFormat == SAMPLEFORMAT_UINT && nPixelBytes == 2 )

    {

        *((uint16 *)pabyData) = (uint16) MAX(0,MIN(65535,dfValue));

    }

    else if( nSampleFormat == SAMPLEFORMAT_UINT && nPixelBytes == 4 )

    {

        *((uint32 *)pabyData) = (uint32) dfValue;

    }

    else if( nSampleFormat == SAMPLEFORMAT_INT && nPixelBytes == 2 )

    {

        *((int16 *)pabyData) = (int16) MAX(-32768,MIN(32767,dfValue));

    }

    else if( nSampleFormat == SAMPLEFORMAT_INT && nPixelBytes == 32 )

    {

        *((int32 *)pabyData) = (int32) dfValue;

    }

    else if( nSampleFormat == SAMPLEFORMAT_IEEEFP && nPixelBytes == 4 )

    {

        *((float *)pabyData) = (float) dfValue;

    }

    else if( nSampleFormat == SAMPLEFORMAT_IEEEFP && nPixelBytes == 8 )

    {

        *((double *)pabyData) = dfValue;

    }

}

/************************************************************************/

/*                          TIFF_DownSample()                           */

/*                                                                      */

/*      Down sample a tile of full res data into a window of a tile     */

/*      of downsampled data.                                            */

/************************************************************************/

static

void TIFF_DownSample( unsigned char *pabySrcTile,

                      uint32 nBlockXSize, uint32 nBlockYSize,

                      int nPixelSkewBits, int nBitsPerPixel,

                      unsigned char * pabyOTile,

                      uint32 nOBlockXSize, uint32 nOBlockYSize,

                      uint32 nTXOff, uint32 nTYOff, int nOMult,

                      int nSampleFormat, const char * pszResampling )

{

    uint32	i, j;

    int         k, nPixelBytes = (nBitsPerPixel) / 8;

    int		nPixelGroupBytes = (nBitsPerPixel+nPixelSkewBits)/8;

    unsigned char *pabySrc, *pabyDst;

    double      *padfSamples;

    assert( nBitsPerPixel >= 8 );

    padfSamples = (double *) malloc(sizeof(double) * nOMult * nOMult);

/* ==================================================================== */

/*      Loop over scanline chunks to process, establishing where the    */

/*      data is going.                                                  */

/* ==================================================================== */

    for( j = 0; j*nOMult < nBlockYSize; j++ )

    {

        if( j + nTYOff >= nOBlockYSize )

            break;

        pabyDst = pabyOTile + ((j+nTYOff)*nOBlockXSize + nTXOff)

            * nPixelBytes * nPixelGroupBytes;

/* -------------------------------------------------------------------- */

/*      Handler nearest resampling ... we don't even care about the     */

/*      data type, we just do a bytewise copy.                          */

/* -------------------------------------------------------------------- */

        if( strncmp(pszResampling,"nearest",4) == 0

            || strncmp(pszResampling,"NEAR",4) == 0 )

        {

            pabySrc = pabySrcTile + j*nOMult*nBlockXSize * nPixelGroupBytes;

            for( i = 0; i*nOMult < nBlockXSize; i++ )

            {

                if( i + nTXOff >= nOBlockXSize )

                    break;

                /*

                 * For now use simple subsampling, from the top left corner

                 * of the source block of pixels.

                 */

                for( k = 0; k < nPixelBytes; k++ )

                    pabyDst[k] = pabySrc[k];

                pabyDst += nPixelBytes * nPixelGroupBytes;

                pabySrc += nOMult * nPixelGroupBytes;

            }

        }

/* -------------------------------------------------------------------- */

/*      Handle the case of averaging.  For this we also have to         */

/*      handle each sample format we are concerned with.                */

/* -------------------------------------------------------------------- */

        else if( strncmp(pszResampling,"averag",6) == 0

                 || strncmp(pszResampling,"AVERAG",6) == 0 )

        {

            pabySrc = pabySrcTile + j*nOMult*nBlockXSize * nPixelGroupBytes;

            for( i = 0; i*nOMult < nBlockXSize; i++ )

            {

                double   dfTotal;

                uint32   nXSize, nYSize, iSample;

                if( i + nTXOff >= nOBlockXSize )

                    break;

                nXSize = MIN((uint32)nOMult,nBlockXSize-i);

                nYSize = MIN((uint32)nOMult,nBlockYSize-j);

                TIFF_GetSourceSamples( padfSamples, pabySrc,

                                       nPixelBytes, nSampleFormat,

                                       nXSize, nYSize,

                                       nPixelGroupBytes,

                                       nPixelGroupBytes * nBlockXSize );

                dfTotal = 0;

                for( iSample = 0; iSample < nXSize*nYSize; iSample++ )

                {

                    dfTotal += padfSamples[iSample];

                }

                TIFF_SetSample( pabyDst, nPixelBytes, nSampleFormat, 

                                dfTotal / (nXSize*nYSize) );

                pabySrc += nOMult * nPixelGroupBytes;

                pabyDst += nPixelBytes;

            }

        }

    }

    free( padfSamples );

}

/************************************************************************/

/*                     TIFF_DownSample_Subsampled()                     */

/************************************************************************/

static

void TIFF_DownSample_Subsampled( unsigned char *pabySrcTile, int nSample,

                                 uint32 nBlockXSize, uint32 nBlockYSize,

                                 unsigned char * pabyOTile,

                                 uint32 nOBlockXSize, uint32 nOBlockYSize,

                                 uint32 nTXOff, uint32 nTYOff, int nOMult,

                                 const char *pszResampling,

                                 int nHorSubsampling, int nVerSubsampling )

{

    /* TODO: test with variety of subsampling values, and incovinient tile/strip sizes */

    int nSampleBlockSize;

    int nSourceSampleRowSize;

    int nDestSampleRowSize;

    uint32  nSourceX, nSourceY;

    uint32  nSourceXSec, nSourceYSec;

    uint32  nSourceXSecEnd, nSourceYSecEnd;

    uint32  nDestX, nDestY;

    int nSampleOffsetInSampleBlock;

    unsigned int nCummulator;

    unsigned int nCummulatorCount;

    nSampleBlockSize = nHorSubsampling * nVerSubsampling + 2;

    nSourceSampleRowSize = 

        ( ( nBlockXSize + nHorSubsampling - 1 ) / nHorSubsampling ) * nSampleBlockSize;

    nDestSampleRowSize = 

        ( ( nOBlockXSize + nHorSubsampling - 1 ) / nHorSubsampling ) * nSampleBlockSize;

    if( strncmp(pszResampling,"nearest",4) == 0

        || strncmp(pszResampling,"NEAR",4) == 0 )

    {

    	if( nSample == 0 )

        {

            for( nSourceY = 0, nDestY = nTYOff; 

                 nSourceY < nBlockYSize; 

                 nSourceY += nOMult, nDestY ++)

            {

                if( nDestY >= nOBlockYSize )

                    break;

                for( nSourceX = 0, nDestX = nTXOff; 

                     nSourceX < nBlockXSize; 

                     nSourceX += nOMult, nDestX ++)

                {

                    if( nDestX >= nOBlockXSize )

                        break;

                    * ( pabyOTile + ( nDestY / nVerSubsampling ) * nDestSampleRowSize

                        + ( nDestY % nVerSubsampling ) * nHorSubsampling

                        + ( nDestX / nHorSubsampling ) * nSampleBlockSize

                        + ( nDestX % nHorSubsampling ) ) =

                        * ( pabySrcTile + ( nSourceY / nVerSubsampling ) * nSourceSampleRowSize

                            + ( nSourceY % nVerSubsampling ) * nHorSubsampling

                            + ( nSourceX / nHorSubsampling ) * nSampleBlockSize

                            + ( nSourceX % nHorSubsampling ) );

                }

            }

        }

        else

        {

            nSampleOffsetInSampleBlock = nHorSubsampling * nVerSubsampling + nSample - 1;

            for( nSourceY = 0, nDestY = ( nTYOff / nVerSubsampling ); 

                 nSourceY < ( nBlockYSize / nVerSubsampling );

                 nSourceY += nOMult, nDestY ++)

            {

                if( nDestY*nVerSubsampling >= nOBlockYSize )

                    break;

            	for( nSourceX = 0, nDestX = ( nTXOff / nHorSubsampling ); 

                     nSourceX < ( nBlockXSize / nHorSubsampling );

                     nSourceX += nOMult, nDestX ++)

                {

                    if( nDestX*nHorSubsampling >= nOBlockXSize )

                        break;

                    * ( pabyOTile + nDestY * nDestSampleRowSize

                        + nDestX * nSampleBlockSize

                        + nSampleOffsetInSampleBlock ) =

                    	* ( pabySrcTile + nSourceY * nSourceSampleRowSize

                            + nSourceX * nSampleBlockSize

                            + nSampleOffsetInSampleBlock );

                }

            }

        }

    }

    else if( strncmp(pszResampling,"averag",6) == 0

             || strncmp(pszResampling,"AVERAG",6) == 0 )

    {

    	if( nSample == 0 )

        {

            for( nSourceY = 0, nDestY = nTYOff; nSourceY < nBlockYSize; nSourceY += nOMult, nDestY ++)

            {

                if( nDestY >= nOBlockYSize )

                    break;

                for( nSourceX = 0, nDestX = nTXOff; nSourceX < nBlockXSize; nSourceX += nOMult, nDestX ++)

                {

                    if( nDestX >= nOBlockXSize )

                        break;

                    nSourceXSecEnd = nSourceX + nOMult;

                    if( nSourceXSecEnd > nBlockXSize )

                        nSourceXSecEnd = nBlockXSize;

                    nSourceYSecEnd = nSourceY + nOMult;

                    if( nSourceYSecEnd > nBlockYSize )

                        nSourceYSecEnd = nBlockYSize;

                    nCummulator = 0;

                    for( nSourceYSec = nSourceY; nSourceYSec < nSourceYSecEnd; nSourceYSec ++)

                    {

                        for( nSourceXSec = nSourceX; nSourceXSec < nSourceXSecEnd; nSourceXSec ++)

                        {

                            nCummulator += * ( pabySrcTile + ( nSourceYSec / nVerSubsampling ) * nSourceSampleRowSize

                                               + ( nSourceYSec % nVerSubsampling ) * nHorSubsampling

                                               + ( nSourceXSec / nHorSubsampling ) * nSampleBlockSize

                                               + ( nSourceXSec % nHorSubsampling ) );

                        }

                    }

                    nCummulatorCount = ( nSourceXSecEnd - nSourceX ) * ( nSourceYSecEnd - nSourceY );

                    * ( pabyOTile + ( nDestY / nVerSubsampling ) * nDestSampleRowSize

                        + ( nDestY % nVerSubsampling ) * nHorSubsampling

                        + ( nDestX / nHorSubsampling ) * nSampleBlockSize

                        + ( nDestX % nHorSubsampling ) ) =

                        ( ( nCummulator + ( nCummulatorCount >> 1 ) ) / nCummulatorCount );

                }

            }

        }

        else

        {

            nSampleOffsetInSampleBlock = nHorSubsampling * nVerSubsampling + nSample - 1;

            for( nSourceY = 0, nDestY = ( nTYOff / nVerSubsampling ); nSourceY < ( nBlockYSize / nVerSubsampling );

                 nSourceY += nOMult, nDestY ++)

            {

                if( nDestY*nVerSubsampling >= nOBlockYSize )

                    break;

                for( nSourceX = 0, nDestX = ( nTXOff / nHorSubsampling ); nSourceX < ( nBlockXSize / nHorSubsampling );

                     nSourceX += nOMult, nDestX ++)

                {

                    if( nDestX*nHorSubsampling >= nOBlockXSize )

                        break;

                    nSourceXSecEnd = nSourceX + nOMult;

                    if( nSourceXSecEnd > ( nBlockXSize / nHorSubsampling ) )

                        nSourceXSecEnd = ( nBlockXSize / nHorSubsampling );

                    nSourceYSecEnd = nSourceY + nOMult;

                    if( nSourceYSecEnd > ( nBlockYSize / nVerSubsampling ) )

                        nSourceYSecEnd = ( nBlockYSize / nVerSubsampling );

                    nCummulator = 0;

                    for( nSourceYSec = nSourceY; nSourceYSec < nSourceYSecEnd; nSourceYSec ++)

                    {

                        for( nSourceXSec = nSourceX; nSourceXSec < nSourceXSecEnd; nSourceXSec ++)

                        {

                            nCummulator += * ( pabySrcTile + nSourceYSec * nSourceSampleRowSize

                                               + nSourceXSec * nSampleBlockSize

                                               + nSampleOffsetInSampleBlock );

                        }

                    }

                    nCummulatorCount = ( nSourceXSecEnd - nSourceX ) * ( nSourceYSecEnd - nSourceY );

                    * ( pabyOTile + nDestY * nDestSampleRowSize

                        + nDestX * nSampleBlockSize

                        + nSampleOffsetInSampleBlock ) =

                        ( ( nCummulator + ( nCummulatorCount >> 1 ) ) / nCummulatorCount );

                }

            }

        }

    }

}

/************************************************************************/

/*                      TIFF_ProcessFullResBlock()                      */

/*                                                                      */

/*      Process one block of full res data, downsampling into each      */

/*      of the overviews.                                               */

/************************************************************************/

void TIFF_ProcessFullResBlock( TIFF *hTIFF, int nPlanarConfig,

                               int bSubsampled,

                               int nHorSubsampling, int nVerSubsampling,

                               int nOverviews, int * panOvList,

                               int nBitsPerPixel,

                               int nSamples, TIFFOvrCache ** papoRawBIs,

                               uint32 nSXOff, uint32 nSYOff,

                               unsigned char *pabySrcTile,

                               uint32 nBlockXSize, uint32 nBlockYSize,

                               int nSampleFormat, const char * pszResampling )

{

    int		iOverview, iSample;

    for( iSample = 0; iSample < nSamples; iSample++ )

    {

        /*

         * We have to read a tile/strip for each sample for

         * PLANARCONFIG_SEPARATE.  Otherwise, we just read all the samples

         * at once when handling the first sample.

         */

        if( nPlanarConfig == PLANARCONFIG_SEPARATE || iSample == 0 )

        {

            if( TIFFIsTiled(hTIFF) )

            {

                TIFFReadEncodedTile( hTIFF,

                                     TIFFComputeTile(hTIFF, nSXOff, nSYOff,

                                                     0, (tsample_t)iSample ),

                                     pabySrcTile,

                                     TIFFTileSize(hTIFF));

            }

            else

            {

                TIFFReadEncodedStrip( hTIFF,

                                      TIFFComputeStrip(hTIFF, nSYOff,

                                                       (tsample_t) iSample),

                                      pabySrcTile,

                                      TIFFStripSize(hTIFF) );

            }

        }

        /*        

         * Loop over destination overview layers

         */

        for( iOverview = 0; iOverview < nOverviews; iOverview++ )

        {

            TIFFOvrCache *poRBI = papoRawBIs[iOverview];

            unsigned char *pabyOTile;

            uint32  nTXOff, nTYOff, nOXOff, nOYOff, nOMult;

            uint32  nOBlockXSize = poRBI->nBlockXSize;

            uint32  nOBlockYSize = poRBI->nBlockYSize;

            int     nSkewBits, nSampleByteOffset; 

            /*

             * Fetch the destination overview tile

             */

            nOMult = panOvList[iOverview];

            nOXOff = (nSXOff/nOMult) / nOBlockXSize;

            nOYOff = (nSYOff/nOMult) / nOBlockYSize;

            if( bSubsampled )

            {

                pabyOTile = TIFFGetOvrBlock_Subsampled( poRBI, nOXOff, nOYOff );

                /*

                 * Establish the offset into this tile at which we should

                 * start placing data.

                 */

                nTXOff = (nSXOff - nOXOff*nOMult*nOBlockXSize) / nOMult;

                nTYOff = (nSYOff - nOYOff*nOMult*nOBlockYSize) / nOMult;

#ifdef DBMALLOC

                malloc_chain_check( 1 );

#endif

                TIFF_DownSample_Subsampled( pabySrcTile, iSample,

                                            nBlockXSize, nBlockYSize,

                                            pabyOTile,

                                            poRBI->nBlockXSize, poRBI->nBlockYSize,

                                            nTXOff, nTYOff,

                                            nOMult, pszResampling,

                                            nHorSubsampling, nVerSubsampling );

#ifdef DBMALLOC

                malloc_chain_check( 1 );

#endif

            }

            else

            {

                pabyOTile = TIFFGetOvrBlock( poRBI, nOXOff, nOYOff, iSample );

                /*

                 * Establish the offset into this tile at which we should

                 * start placing data.

                 */

                nTXOff = (nSXOff - nOXOff*nOMult*nOBlockXSize) / nOMult;

                nTYOff = (nSYOff - nOYOff*nOMult*nOBlockYSize) / nOMult;

                /*

                 * Figure out the skew (extra space between ``our samples'') and

                 * the byte offset to the first sample.

                 */

                assert( (nBitsPerPixel % 8) == 0 );

                if( nPlanarConfig == PLANARCONFIG_SEPARATE )

                {

                    nSkewBits = 0;

                    nSampleByteOffset = 0;

                }

                else

                {

                    nSkewBits = nBitsPerPixel * (nSamples-1);

                    nSampleByteOffset = (nBitsPerPixel/8) * iSample;

                }

                /*

                 * Perform the downsampling.

                 */

#ifdef DBMALLOC

                malloc_chain_check( 1 );

#endif

                TIFF_DownSample( pabySrcTile + nSampleByteOffset,

                               nBlockXSize, nBlockYSize,

                               nSkewBits, nBitsPerPixel, pabyOTile,

                               poRBI->nBlockXSize, poRBI->nBlockYSize,

                               nTXOff, nTYOff,

                               nOMult, nSampleFormat, pszResampling );

#ifdef DBMALLOC

                malloc_chain_check( 1 );

#endif

            }

        }

    }

}

/************************************************************************/

/*                        TIFF_BuildOverviews()                         */

/*                                                                      */

/*      Build the requested list of overviews.  Overviews are           */

/*      maintained in a bunch of temporary files and then these are     */

/*      written back to the TIFF file.  Only one pass through the       */

/*      source TIFF file is made for any number of output               */

/*      overviews.                                                      */

/************************************************************************/

void TIFFBuildOverviews( TIFF *hTIFF, int nOverviews, int * panOvList,

                         int bUseSubIFDs, const char *pszResampleMethod,

                         int (*pfnProgress)( double, void * ),

                         void * pProgressData )

{

    TIFFOvrCache	**papoRawBIs;

    uint32		nXSize, nYSize, nBlockXSize, nBlockYSize;

    uint16		nBitsPerPixel, nPhotometric, nCompressFlag, nSamples,

        nPlanarConfig, nSampleFormat;

    int         bSubsampled;

    uint16      nHorSubsampling, nVerSubsampling;

    int			bTiled, nSXOff, nSYOff, i;

    unsigned char	*pabySrcTile;

    uint16		*panRedMap, *panGreenMap, *panBlueMap;

    TIFFErrorHandler    pfnWarning;

    (void) pfnProgress;

    (void) pProgressData;

/* -------------------------------------------------------------------- */

/*      Get the base raster size.                                       */

/* -------------------------------------------------------------------- */

    TIFFGetField( hTIFF, TIFFTAG_IMAGEWIDTH, &nXSize );

    TIFFGetField( hTIFF, TIFFTAG_IMAGELENGTH, &nYSize );

    TIFFGetField( hTIFF, TIFFTAG_BITSPERSAMPLE, &nBitsPerPixel );

    /* TODO: nBitsPerPixel seems misnomer and may need renaming to nBitsPerSample */

    TIFFGetField( hTIFF, TIFFTAG_SAMPLESPERPIXEL, &nSamples );

    TIFFGetFieldDefaulted( hTIFF, TIFFTAG_PLANARCONFIG, &nPlanarConfig );

    TIFFGetFieldDefaulted( hTIFF, TIFFTAG_PHOTOMETRIC, &nPhotometric );

    TIFFGetFieldDefaulted( hTIFF, TIFFTAG_COMPRESSION, &nCompressFlag );

    TIFFGetFieldDefaulted( hTIFF, TIFFTAG_SAMPLEFORMAT, &nSampleFormat );

    if( nPhotometric == PHOTOMETRIC_YCBCR || nPhotometric == PHOTOMETRIC_ITULAB )

    {

        if( nBitsPerPixel != 8 || nSamples != 3 || nPlanarConfig != PLANARCONFIG_CONTIG ||

            nSampleFormat != SAMPLEFORMAT_UINT)

        {

            /* TODO: use of TIFFError is inconsistent with use of fprintf in addtiffo.c, sort out */

            TIFFErrorExt( TIFFClientdata(hTIFF), "TIFFBuildOverviews",

                          "File `%s' has an unsupported subsampling configuration.\n",

                          TIFFFileName(hTIFF) );

            /* If you need support for this particular flavor, please contact either

             * Frank Warmerdam warmerdam@pobox.com

             * Joris Van Damme info@awaresystems.be

             */

            return;

        }

        bSubsampled = 1;

        TIFFGetField( hTIFF, TIFFTAG_YCBCRSUBSAMPLING, &nHorSubsampling, &nVerSubsampling );

        /* TODO: find out if maybe TIFFGetFieldDefaulted is better choice for YCbCrSubsampling tag */

    }

    else

    {

        if( nBitsPerPixel < 8 )

        {

            /* TODO: use of TIFFError is inconsistent with use of fprintf in addtiffo.c, sort out */

            TIFFErrorExt( TIFFClientdata(hTIFF), "TIFFBuildOverviews",

                          "File `%s' has samples of %d bits per sample.  Sample\n"

                          "sizes of less than 8 bits per sample are not supported.\n",

                          TIFFFileName(hTIFF), nBitsPerPixel );

            return;

        }

        bSubsampled = 0;

        nHorSubsampling = 1;

        nVerSubsampling = 1;

    }

/* -------------------------------------------------------------------- */

/*      Turn off warnings to avoid alot of repeated warnings while      */

/*      rereading directories.                                          */

/* -------------------------------------------------------------------- */

    pfnWarning = TIFFSetWarningHandler( NULL );

/* -------------------------------------------------------------------- */

/*      Get the base raster block size.                                 */

/* -------------------------------------------------------------------- */

    if( TIFFGetField( hTIFF, TIFFTAG_ROWSPERSTRIP, &(nBlockYSize) ) )

    {

        nBlockXSize = nXSize;

        bTiled = FALSE;

    }

    else

    {

        TIFFGetField( hTIFF, TIFFTAG_TILEWIDTH, &nBlockXSize );

        TIFFGetField( hTIFF, TIFFTAG_TILELENGTH, &nBlockYSize );

        bTiled = TRUE;

    }

/* -------------------------------------------------------------------- */

/*	Capture the pallette if there is one.				*/

/* -------------------------------------------------------------------- */

    if( TIFFGetField( hTIFF, TIFFTAG_COLORMAP,

                      &panRedMap, &panGreenMap, &panBlueMap ) )

    {

        uint16		*panRed2, *panGreen2, *panBlue2;

        int             nColorCount = 1 << nBitsPerPixel;

        panRed2 = (uint16 *) _TIFFmalloc(2*nColorCount);

        panGreen2 = (uint16 *) _TIFFmalloc(2*nColorCount);

        panBlue2 = (uint16 *) _TIFFmalloc(2*nColorCount);

        memcpy( panRed2, panRedMap, 2 * nColorCount );

        memcpy( panGreen2, panGreenMap, 2 * nColorCount );

        memcpy( panBlue2, panBlueMap, 2 * nColorCount );

        panRedMap = panRed2;

        panGreenMap = panGreen2;

        panBlueMap = panBlue2;

    }

    else

    {

        panRedMap = panGreenMap = panBlueMap = NULL;

    }

/* -------------------------------------------------------------------- */

/*      Initialize overviews.                                           */

/* -------------------------------------------------------------------- */

    papoRawBIs = (TIFFOvrCache **) _TIFFmalloc(nOverviews*sizeof(void*));

    for( i = 0; i < nOverviews; i++ )

    {

        uint32  nOXSize, nOYSize, nOBlockXSize, nOBlockYSize;

        toff_t  nDirOffset;

        nOXSize = (nXSize + panOvList[i] - 1) / panOvList[i];

        nOYSize = (nYSize + panOvList[i] - 1) / panOvList[i];

        nOBlockXSize = MIN(nBlockXSize,nOXSize);

        nOBlockYSize = MIN(nBlockYSize,nOYSize);

        if( bTiled )

        {

            if( (nOBlockXSize % 16) != 0 )

                nOBlockXSize = nOBlockXSize + 16 - (nOBlockXSize % 16);

            if( (nOBlockYSize % 16) != 0 )

                nOBlockYSize = nOBlockYSize + 16 - (nOBlockYSize % 16);

        }

        nDirOffset = TIFF_WriteOverview( hTIFF, nOXSize, nOYSize,

                                         nBitsPerPixel, nPlanarConfig,

                                         nSamples, nOBlockXSize, nOBlockYSize,

                                         bTiled, nCompressFlag, nPhotometric,

                                         nSampleFormat,

                                         panRedMap, panGreenMap, panBlueMap,

                                         bUseSubIFDs,

                                         nHorSubsampling, nVerSubsampling );

        papoRawBIs[i] = TIFFCreateOvrCache( hTIFF, nDirOffset );

    }

    if( panRedMap != NULL )

    {

        _TIFFfree( panRedMap );

        _TIFFfree( panGreenMap );

        _TIFFfree( panBlueMap );

    }

/* -------------------------------------------------------------------- */

/*      Allocate a buffer to hold a source block.                       */

/* -------------------------------------------------------------------- */

    if( bTiled )

        pabySrcTile = (unsigned char *) _TIFFmalloc(TIFFTileSize(hTIFF));

    else

        pabySrcTile = (unsigned char *) _TIFFmalloc(TIFFStripSize(hTIFF));

/* -------------------------------------------------------------------- */

/*      Loop over the source raster, applying data to the               */

/*      destination raster.                                             */

/* -------------------------------------------------------------------- */

    for( nSYOff = 0; nSYOff < (int) nYSize; nSYOff += nBlockYSize )

    {

        for( nSXOff = 0; nSXOff < (int) nXSize; nSXOff += nBlockXSize )

        {

            /*

             * Read and resample into the various overview images.

             */

            TIFF_ProcessFullResBlock( hTIFF, nPlanarConfig,

                                      bSubsampled,nHorSubsampling,nVerSubsampling,

                                      nOverviews, panOvList,

                                      nBitsPerPixel, nSamples, papoRawBIs,

                                      nSXOff, nSYOff, pabySrcTile,

                                      nBlockXSize, nBlockYSize,

                                      nSampleFormat, pszResampleMethod );

        }

    }

    _TIFFfree( pabySrcTile );

/* -------------------------------------------------------------------- */