Keeping proprietary tags in tiff file

[arnoques]

Hi, everyone!
I'm trying to compress many tiff images to save some space. I'm using

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convert input.tif -compress Zip output.tif

Like many others before, I get the "unknown field with tag 34118 (0x8546) encountered. `TIFFReadDirectory' @ warning". I guess you must be tired of questions about it, but I promise this one is different.

My problem is that convert strips the proprietary tag, but I need to keep them because they have information about the parameters used in the microscope when taking the image. Is there any way to do that?

Thanks!

Some data of these images:

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tiffinfo input.tif
TIFF Directory at offset 0x8 (8)
  Subfile Type: (0 = 0x0)
  Image Width: 1024 Image Length: 768
  Resolution: 1, 1 (unitless)
  Bits/Sample: 8
  Compression Scheme: None
  Photometric Interpretation: palette color (RGB from colormap)
  Samples/Pixel: 1
  Rows/Strip: (infinite)
  Planar Configuration: single image plane
  Color Map: (present)
  Tag 34118: 0
0
0
1.464848e-00
...and many more lines

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tiffinfo output.tif
TIFF Directory at offset 0x9784c (620620)
  Image Width: 1024 Image Length: 768
  Resolution: 1, 1 (unitless)
  Bits/Sample: 8
  Compression Scheme: AdobeDeflate
  Photometric Interpretation: palette color (RGB from colormap)
  FillOrder: msb-to-lsb
  Orientation: row 0 top, col 0 lhs
  Samples/Pixel: 1
  Rows/Strip: 768
  Planar Configuration: single image plane
  Page Number: 0-1
  Color Map: (present)
  DocumentName: Q32_cm4989.tif.tmp
  White Point: 0.3127-0.329
  PrimaryChromaticities: 0.640000,0.330000,0.300000,0.600000,0.150000,0.060000

[anthony]

My understanding is the IM should keep unknown tags, unless striped. At least TIFF to TIFF

I would report this in Bugs.