2000.06.10 15:11 "Re: Add: Resized version", by Frank Warmerdam
In fact, Compression tag is also missing for IFDs 1 to 5. libtiff concluded uncompressed data (default), but "optirastoras" meant Fax4 - as specified for the full size bitmap stored in IFD 0. That was actually the cause for TIFFReadTile() to fail with IFD 5 (should have debugged it).
Anyway, I am still asking for your opinions about "industry standard" usage and support for multiresolution TIFF images. E.g., which standard apps would create them, do they allow for user to specify what resized bitmaps to create, of which photometric type, etc. Also, do you know of multiple page TIFF files containing resized versions for some/all of its pages. I.e., some IFD tags would have bit 0 raised up, some bit 1 raised up, and some both (?!) - not to mention their possible masks: NewSubfileType bit 2 raised up. I am still not sure would that be compliant with TIFF rev. 5 (6), not to mention which standard apps would support them. Specially I am not quite sure which standard TIFF readers actually use those resize bitmaps to speed up stretching and so. And for TIFF editors: would they then really update both the original image and its resized version(s)?!
I would agree with your assessment that the optiras images are broken. To my understanding the reduced resolution images are required to be fully formed images on their own, with their IFD fulfilling all the normal TIFF requirements.
I don't know much about the document imaging area or some other TIFF applications, but there is some use of multi-resolution TIFF files in the satellite imaging area. For instance the PCI, Intergraph and Global Geomatics GeoTIFF readers all support reduced resolution images for accelerated display.
I have written a small application called ``tiffaddo'', found in the libtiff/contrib directory for building reduced resolution images; however, it only works for images with eight or more bits per pixel.
It is my hope that satellite (and airphoto) data providers who ship GeoTIFF files now can be persuaded in time to ship images with reduced resolution overviews.
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