如何使用 openJPEG C++ 逐块读取 JP2

Question

我想知道：逐块读取 jp2 并将数据存储在缓冲区对象中的意图是什么？

现在我正在做类似的事情。

/* note I already created stream and configured decoder and resolution factor is set to 0 */

opj_codestream_index_t *pJP2CodeStreamIndex = opj_get_cstr_index(pJP2Codec);
opj_codestream_info_v2_t *pJP2CodeStreamInfo = opj_get_cstr_info(pJP2Codec);

CDrawRect myRect
GetDrawRect(&myRect);

int start_x = myRect.left;
int start_y = myRect.top;
int end_x = myRect.right;
int end_y = myRect.bottom;

int StartXTile = start_x / pJP2CodeStreamInfo->tdx;
int StartYTile = start_y / pJP2CodeStreamInfo->tdy;
int EndXTile = ceil((float)end_x / (float)pJP2CodeStreamInfo->tdx);
int EndYTile = ceil((float)end_y / (float)pJP2CodeStreamInfo->tdy);

std::vector<int> TilesToDecode;
for(int i = StartXTile; i < EndXTile; i++)
    for(int j = StartYTile; j < EndYTile; j++)
    {
        int TileNo = i+ j*pJP2CodeStreamInfo->tw;
        TilesToDecode.push_back(TileNo);
    }

for(std::vector<int>::iter Iter = TilesToDecode.begin(); Iter != TilesToDecode.end(); Iter++)
{
    opj_get_decoded_tile(pJP2Codec, pJP2Stream, pJP2Image, (OPJ_UINT32)TileNo);
}

/* some time later, i got read buffer for one component */
while (pDst != pEndDst)
{
    OPJ_UINT32* pSrc = pJP2Image.comps[NumComp].data;
    *pDst = (int)*pSrc;
    pDst += stepDst;
    pSrc += stepSrc;
}

但它是如何设计的？

Answer 1

嗯，其实很简单。你只需要注意指针数学和缓冲区的大小。

/代码是用 C++ 编写的，支持 MFC 和 WINAPI/

首先你需要开始解码：

opj_stream_t* pJP2Stream = NULL;
opj_codec_t* pJP2Codec = NULL;
opj_image_t* pJP2Image = NULL;
opj_dparameters_t jp2dParams;

pJP2Stream = opj_stream_create_default_file_stream(LPCTSTR2PCHAR(Filename), OPJ_TRUE);
if(!pJP2Stream)
{
    pFileInfo->ErrorCode = ERR_OPEN;
    return FALSE;
}

strExt = PathFindExtension(Filename);
if(!strExt.CompareNoCase(_T(".JP2")))
    pJP2Codec = opj_create_decompress(OPJ_CODEC_JP2);
if(!strExt.CompareNoCase(_T(".J2K")))
    pJP2Codec = opj_create_decompress(OPJ_CODEC_J2K);
if(!strExt.CompareNoCase(_T(".JPP")))
    pJP2Codec = opj_create_decompress(OPJ_CODEC_JPP);
if(!strExt.CompareNoCase(_T(".JPT")))
    pJP2Codec = opj_create_decompress(OPJ_CODEC_JPT);
if(!strExt.CompareNoCase(_T(".JPX")))
    pJP2Codec = opj_create_decompress(OPJ_CODEC_JPX);

if(!pJP2Codec)
{
    opj_stream_destroy(pJP2Stream);
    opj_destroy_codec(pJP2Codec);
    return FALSE;
}

//register callbacks
opj_set_info_handler(pJP2Codec, info_callback,00);
opj_set_warning_handler(pJP2Codec, warning_callback,00);
opj_set_error_handler(pJP2Codec, error_callback,00);

opj_set_default_decoder_parameters(&jp2dParams);
if ( !opj_setup_decoder(pJP2Codec, &jp2dParams) )
{
    //(stderr, "ERROR -> opj_compress: failed to setup the decoder\n");
    opj_stream_destroy(pJP2Stream);
    opj_destroy_codec(pJP2Codec);
    return FALSE;
}

if( !opj_read_header(pJP2Stream, pJP2Codec, &pJP2Image) || (pJP2Image->numcomps == 0))
{

    opj_stream_destroy(pJP2Stream);
    opj_destroy_codec(pJP2Codec);
    if (pJP2Image)
        opj_image_destroy(pJP2Image);
    return FALSE;
}

其次你应该阅读CodestreamInfo：

opj_codestream_info_v2_t *pJP2CodeStreamInfo = opj_get_cstr_info(pJP2Codec);

请注意，如果您有多个线程调用此函数，您可能会发生内存泄漏。所以我建议下一个代码将信息传输到堆栈内存中：

opj_codestream_info_v2_t JP2CodeStreamInfo;
opj_codestream_info_v2_t *pJP2CodeStreamInfo = NULL;

pJP2CodeStreamInfo = opj_get_cstr_info(pJP2Codec);
if(pJP2CodeStreamInfo)
{
    JP2CodeStreamInfo = *pJP2CodeStreamInfo;
    opj_destroy_cstr_info(&pJP2CodeStreamInfo);
}
else
    return FALSE;

当您更改解码分辨率因子时，码流信息会发生变化：

 opj_set_decoded_resolution_factor(pJP2Codec, nResFactor);

分辨率系数 - 使解码图像按 2^nResFactor 比率变小，仅加载 2^n 行和列中的第一个。

我提供下一个代码作为将任何图块复制到任何图像块的通用解决方案。

        long posSrcOffsetX = (start_x > JP2Image.comps[NumBand].x0 ? (start_x - JP2Image.comps[NumBand].x0) : 0) >> JP2Image.comps[NumBand].factor >> (iDifRes);
        long posSrcOffsetY = (start_y > JP2Image.comps[NumBand].y0 ? (start_y - JP2Image.comps[NumBand].y0) : 0) >> JP2Image.comps[NumBand].factor >> (iDifRes);
        long posDstOffsetX = ((JP2Image.comps[NumBand].x0 > start_x? JP2Image.comps[NumBand].x0 - start_x : 0) >> JP2Image.comps[NumBand].factor >> (iDifRes)) ;
        long posDstOffsetY = ((JP2Image.comps[NumBand].y0 > start_y? JP2Image.comps[NumBand].y0 - start_y : 0) >> JP2Image.comps[NumBand].factor >> (iDifRes)) ;

        long posSrcEndX = (bInnerBlock ? ((JP2Image.comps[NumBand].x0 >> JP2Image.comps[NumBand].factor) + (end_x >> JP2Image.comps[NumBand].factor)) : JP2Image.comps[NumBand].w) >>(iDifRes) ;
        long posSrcEndY = (bInnerBlock ? ((JP2Image.comps[NumBand].y0 >> JP2Image.comps[NumBand].factor) + (end_y >> JP2Image.comps[NumBand].factor)) : JP2Image.comps[NumBand].h) >>(iDifRes) ;

        long TileEndX = JP2Image.comps[NumBand].x0 + (JP2Image.comps[NumBand].w << JP2Image.comps[NumBand].factor);
        long TileEndY = JP2Image.comps[NumBand].y0 + (JP2Image.comps[NumBand].h << JP2Image.comps[NumBand].factor);

        long posDstEndX = (TileEndX > end_x ? end_x - start_x : TileEndX - start_x) >> JP2Image.comps[NumBand].factor >> (iDifRes) ;
        long posDstEndY = (TileEndY > end_y ? end_y - start_y : TileEndY - start_y) >> JP2Image.comps[NumBand].factor >> (iDifRes) ;

        long stepSrcX = 1 << (iDifRes);
        long stepSrcY = JP2Image.comps[NumBand].w << (iDifRes);
        long stepDstX = 1;
        long stepDstY = 64;

        DWORD boundX = posDstEndX - posDstOffsetX;
        DWORD boundY = posDstEndY - posDstOffsetY;

        for(i = 0 ; i < boundY ; i++ )
                    {
                        pSrc = JP2Image.comps[NumBand].data + (posSrcOffsetX)*stepSrcX + ((posSrcOffsetY+i) * stepSrcY);
                        pDst = pDstLine + (posDstOffsetX + ((posDstOffsetY+i) * stepDstY))*PixelSize;
                        for ( j = 0; j < boundX ; j++ )
                        {
                            iValue = *(pSrc + j* stepSrcX);

                            iValue += JP2Image.comps[NumBand].sgnd ? (1 << (JP2Image.comps[NumBand].prec - 1)) : 0; 

                            if (iValue > dMax)
                                iValue = (int)dMax; 
                            else 
                                if (iValue < dMin) 
                                    iValue = (int)dMin;

                            UCHAR bufVal = (UCHAR)iValue;
                            *(UCHAR*)pDst = (UCHAR)iValue;

                            pDst += stepDstX*PixelSize;
                        }
                    }

只需确保检查每个像素的位数并为所有图像组件设置一个 for 子句。

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