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TIFF and LibTiff Mail List Archive

Thread

2004.01.19 17:01 "[Tiff] Packbits errors", by Bernd Stahlbock
2004.01.19 17:21 "Re: [Tiff] Packbits errors", by Frank Warmerdam
2004.01.20 08:25 "RE: [Tiff] Packbits errors", by Bernd Stahlbock
2004.01.20 14:47 "Re: [Tiff] Packbits errors", by Frank Warmerdam

2004.01.20 08:25 "RE: [Tiff] Packbits errors", by Bernd Stahlbock

Frank,

the files are OK, if they are re-read the display error disappears. Therefore I would say that

  1. there is a bug in our code for displaying the image data, or
  2. sometimes we have read errors from the disk

As we see these errors only with Packbits I would rule out no. 1. Is it possible to have sporadic read errors on modern computers that would cause bit errors during image decoding? The images are quite big, up to several 100MB.

best regards
Bernd

> -----Original Message-----
> From: tiff-admin@remotesensing.org
> [mailto:tiff-admin@remotesensing.org] On Behalf Of Frank Warmerdam

Dear Ladies and Gentlemen,
dear programmers,

I have some rare reading errors with packbit compressed files. I get no error message, but the images have some small image corruptions where pixels are shifted to the right a little bit. Sometimes only one line, sometimes maybe 300 or more. The next time I read the image, the display is without errors.

Are there any known errors like this for packbits? Doesn't have packbits an error correction?

Packbits does not include any error correction, but if the data is corrupted in some way you should get the same results each time. If you have a file demonstrating this problem file the bug in bugzilla and Andrey can try and reproduce it. He could also run it through valgrind which may ferret out subtle memory initialization bugs.

I would note the packbits decoder is really quite simple, and it is surprising there would be a bug in it after all these years.

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