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2004.12.09 13:38 "Re: Q: writing tiled TIFFs", by Chris Losinger
> > 256x256 is apparently the LibTiff default. why does LibTiff choose
> > that for a 200x200 image ? i don't know.
>
> How do you arrive at this 'LibTiff default'?
// set image dims
TIFFSetField(tiff, TIFFTAG_IMAGEWIDTH, (uint32) nWidth);
TIFFSetField(tiff, TIFFTAG_IMAGELENGTH, (uint32) nHeight);
// get default tile size
uint32 tilewidth, tileheight;
tilewidth = 0;
tileheight = 0;
TIFFDefaultTileSize(tiff, &tilewidth, &tileheight);
// use that size
TIFFSetField(tiff, TIFFTAG_TILEWIDTH, tilewidth);
TIFFSetField(tiff, TIFFTAG_TILELENGTH, tileheight);
> I generally decide on the tile size myself, and set TIFFTAG_TILEWIDTH and
> TIFFTAG_TILELENGTH tags before using the actual raster write functions.
> Are you doing that?
no, because i assumed LibTiff would generate a reasonable default
tile size, similar to the way it generates reasonable default strip sizes.
> If not, perhaps you should try that and see if it solves your
> problem. If you are doing that, or if it doesn't solve your problem, perhaps you
> could post a code snippet, then maybe we'll be able to see what's going on.
the image i'm using is 8 bits per pixel.
the tile setup part is above. the actual tile writing part looks
like this:
// need a single tile to hold a copy of the source data
TIFFGetField(pCTIS->tiff, TIFFTAG_TILELENGTH, &th);
TIFFGetField(pCTIS->tiff, TIFFTAG_TILEWIDTH, &tw);
ISByteArray tempTile;
tempTile.SetSize(TIFFTileSize(pCTIS->tiff));
if (tempTile.GetPtr() == NULL)
{
return IS_ERR_MEM;
}
for (UINT32 y = 0; y < nHeight; y+=th)
{
for (UINT32 x = 0; x < nWidth; x+=tw)
{
// copy a square part of the source image (or as much of it as we can)
// to the tile buffer.
CISOverlay io;
io.OverlayImage(tempTile, tw, th, // output
pImg, nWidth, nHeight, // input (250x200, in this case)
-x, -y, // position the source image 'over' the tile buffer
1.0, pCTIS->bitDepth / 8,
TIFFTileRowSize(pCTIS->tiff), // number of bytes in tile buffer row
rowStride, // number of bytes in source image row
0);
if (TIFFWriteTile(pCTIS->tiff, tempTile.GetPtr(), x, y, 0, 0) == -1)
{
m_error=IS_ERR_FILEWRITE;
return FALSE;
}
}
}
----
Chris Losinger
losinger@earthlink.net
smallest@smalleranimals.com http://www.smalleranimals.com