2008.01.10 19:03 "[Tiff] LibTiff..Reading partial strips", by Nikhil Shirahatti

2008.01.12 09:32 "Re: [Tiff] Scanline access in libtiff", by


Joris wrote:

TIFFReadScanline and that sort of access might be more optimally streaming. But support for it depends on the particular subcodec, and I seem to remember not all subcodecs support it. It does not work on tiled images, either, and since there's no actual definition in the man pages of what should be returned on subsampled images, there's a bit of a mess in that case. So I essentially regard this scanline based access a broken concept in LibTiff.

Richard Nolde wrote:

I know that you know much more about TIFF and libtiff than I do, but I found the basic functions of reading by tile or scanline to work extremely well in my application tiffcrop. I know that it is being used by folks running fax services and by at least one scanner /digital camera programmer in addition to my own adaptation in a high volume automated bar code reader. I think it might be more correct to say that the scanline interface is limited in its handling of color spaces and possibly certain compression schemes, but I've yet to receive any complaints on performance or failure to handle a TIFF file. I do have the advantage of a large multiprocessor machine with 64 GB of memory, but there are hundreds of concurrent users and most of our files only run in the 250 page range, which with G4 compression on Bilevel images means they are only 20 to 30 MB each.

That seems about right. You're not using the scanline access on tiled images. If some subcodecs use larger buffers then is necessary for scanline access, they still work for you. And you've probably not seen subsampled images through this interface yet, and/or you deal with them as if they were broken.

I didn't mean to say TIFFReadScanline is useless. I meant to say that, as a concept, it's broken, as it has not been maintained into the tiles update of TIFF, the level of support on the part of the subcodec is not guaranteed, and we haven't bothered (yet?) to clear up the mess of scanline based access to subsampled images. It would be interesting to see if and how an unsuspecting interface survives such images, so if you're interested to run a test I'll post you some if you like.

Best regards,

Joris Van Damme
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