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April 2006
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2006.04.17 22:25 "Re: TIFFReadScanline with JPEG compression", by Joris Van Damme
Jason, Jason Summers wrote: > Joris wrote: > > Jason Summers wrote: > > > I'm having trouble getting libtiff's TIFFReadScanline function to > > > work ... > > > > If your need is urgent, I recommend using strip access without > > JPEGCOLORMODE_RGB. That part was recently serviced, and should work > > fine (as you seem to indicate). For other approaches, please feel > > free to file a bug report in BugZilla, and post a follow-up with > > the exact URL of the BugZilla entry here. I'll try and deal with it > > as soon as I can. > > Thanks for the reply. It's not important, but I did some more testing > and filed some bug reports anyway. Thank you for doing so, I believe it will be helpful. > <http://bugzilla.remotesensing.org/show_bug.cgi?id=1158> > <http://bugzilla.remotesensing.org/show_bug.cgi?id=1159> These seem to refer to known issues. As mentioned, strip/tile access without the evil JPEGCOLORMODE_RGB is revised and should work. I believe someone, possibly me, will revise the other parts some time in the future. > <http://bugzilla.remotesensing.org/show_bug.cgi?id=1160> This issue was unknown to me. It's an OJPEG issue, and I didn't think there were any... Many thanks for this bugreport in particular. The file attached to the bugreport *does* get decoded perfectly fine using strip/tile access. It does seem though that I failed to foresee access with TIFFReadScanline... I'm not sure, actually, how to proceed to cure this. Most OJPEG imagery is subsampled YCbCr. What is TIFFReadScanline even supposed to return if decoded data is packed in multiples of subsampling_ver scanlines? Is that even supposed to make sense somehow, is there a particular expected behavior, or is TIFFReadScanline only supposed to work on data that is not subsampled? I will do some thinking on this, and try to resolve this issue in particular very soon, as tif_ojpeg was already supposed to be bugfree. Best regards, Joris Van Damme info@awaresystems.be http://www.awaresystems.be/ Download your free TIFF tag viewer for windows here: http://www.awaresystems.be/imaging/tiff/astifftagviewer.html