[gdal-dev] Read from Erdas Img too slow,

[Jiang Wang]

Hi,
My gdal is 1.8.0.I use GDALDataset::RasterIO to read from a img file .The
file size is 30G bytes ,three bands,data type is GDT_Byte and have 8
overviews.When overview is used or there is no need to resample ,it`s
fast.But when resample is needed,i found gdal copy pixel data 1 byte by 1
byte in fllow codes:
                        memcpy( ((GByte *) pData) + iBandBufOffset,
                                pabySrcBlock + iSrcOffset, nBandDataSize );
Codes is in rasterio.cpp at 2150 lines.
My question is why copy 1 byte at one time.and how  to improve it..
Thanks.
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