Magick++ tiff loses compression

[ths71]

on current IM 6.8.8.7, when you do

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image.read("group4.tif");
image.write("test.tif");

the resulting image is not compressed anymore.

if you insert

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image.compressType(image.compressType());

it has indeed the same compression as the source.

i traced this back to this change:
http://trac.imagemagick.org/changeset/1 ... ers/tiff.c
which in my opinion doesn't make any sense.

in

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    compression=UndefinedCompression;  
    if (image_info->compression != UndefinedCompression)  
      compression=image_info->compression;  

the first two lines are redundant, anyway.

[fmw42]

There was a decision made at that time to not pass on the compression, so as not to decompress and recompress, esp with JPG compression, and thus lose more quality.

[susannamoore]

When it comes to TIFF, two main image compression options are available–they’re known as LZW or ZIP. Both ZIP and LZW are lossless compression methods. That means that no data is being lost in the image compression[/color][/url] process, unlike a lossy format like JPG. But there are two main reasons you might not to use ZIP or LZW compression. Because they require more processing to open and close them, compressed TIFF files can be a little slower to work with.

[ths71]

that's all well and good, but if you want to change compression, it's easy to do so. if you want to retain the settings of the original, not changing anything is the intuitive thing.

image.compressType(image.compressType());

is not a code that seems like it should do anything, but it does.

[dlemstra]

I just committed a patch for this that only make sure that jpeg compression is not used when converting jpeg to tiff. The next release of ImageMagick (6.8.9-2) will include this fix.