1999.06.08 21:58 "RE: Large File Support", by Ed Grissom

Peter -

Although your question was not addressed to me, I'll give you my input anyway....

For uncompressed files, the limit has already been passed. Our photogrammetric scanner is capable of scanning a 10"x10" aerial photo negative at 3500 DPI in 24bit RGB. With a full set of overviews (required for our workflows), this comes out to nearly 5GB uncompressed. Any enhancements we might do to this product ( increase DPI, increase bit depth, etc.) will only make the problem more pronounced.

Unfortunately, compression is often not an option. PackBits does a pretty lousy job on scanned photos, and is essentially unusable for >8bit data. LZW is patented and both LZW and Deflate will typically only reduce these types of images to ~75% of the original size.

JPEG has been our savior so far, but some folks (especially in Remote Sensing) are very particular about original pixel values and do not want to use JPEG compression which modifies the data - however slight the modification is.

I have here on my desk two CD's, each containing a Wavelet compressed file (LizardTech) that would be over 15GB uncompressed. These were created as a mosaic of over a hundred TIFF files. Although the wavelet compression gets them down to less than 650MB, there is nothing comparable in TIFF that would allow me to convert these files (in their entirety) to TIFF.

Recently a customer claimed to have a 40GB (uncompressed) file that he wanted to convert to TIFF. If I remember correctly, it was 6GB compressed. I am not sure what file format was used, perhaps NITF (NITF handles up to 17GB compressed).

If you ask me, Frank was understating the problem. :)

--
ed grissom
egrissom@ziimaging.com