Message-ID: 000e01c05f9c$faea2640$720a0a0a@mediacy.com
To: <tiff@olympiakos.com>
Subject: Garbage for first write to TIFF
From: "Sean Finn" <sean@mediacy.com>
Date: Wed, 6 Dec 2000 10:55:39 -0500
Importance: Normal
Sender: owner-tiff@olympiakos.com


Hi all,

Ok, I am writing a simple 8-bit unsigned char tiff file via Strips and LZW
with Differencing (Predictor=2) encoding. (I have an LZW license).  The
problem is that my first hunk of data that I send to the library to be
written is always being corrupted.  No errors or warnings are returned, but
when I look at it later, it is static mess, and every strip/scanline after
is ok.

here are the tags I am setting prior to writing:

TIFFTAG_IMAGEWIDTH      = image width
TIFFTAG_IMAGELENGTH     = image length
TIFFTAG_BITSPERSAMPLE   = 8
TIFFTAG_SAMPLESPERPIXEL = 1
TIFFTAG_PHOTOMETRIC     = MinIsBlack
TIFFTAG_COMPRESSION     = LZW
TIFFTAG_ORIENTATION     = ORIENTATION_TOPLEFT
TIFFTAG_PLANARCONFIG    = 1
TIFFTAG_RESOLUTIONUNIT  = 2 /* inches */
TIFFTAG_XRESOLUTION
TIFFTAG_XRESOLUTION
TIFFTAG_SAMPLEFORMAT    = 1 /* unsigned char */
TIFFTAG_ROWSPERSTRIP    = TIFFDefaultStripSize(tif, -1)

Then I call TIFFWriteBufferSetup() and TIFFWriteCheck

Then, I walk through my data with TIFFWriteEncodedStrip.

The only thing I can think of that the calculations being made for the
offsets and all the LZW stuff are not being correctly set because the first
call to TIFFWriteEncodedStrip always sets things to 0 (being the first
strip), and that maybe that messes something up.

This behavior has been shown with 8-bit color and Mono (minIsBlack), with
LZW or Deflate compression.  No other types have been tested yet.  But,
uncompressed had no garbage in the first line/s.

Anyway, the tutorial stuff in libtiff is nice, but there is no write info,
just simple read info.  Kind of annoying :)

Any help would be SUPER DUPER appreciated,

Thanks,

Sean
sean@mediacy.com


