[Kde-imaging] [Bug 146259] Raw Converter won't convert to 16bit PNG

[Gilles Caulier]

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------- Additional Comments From caulier.gilles gmail com  2007-09-23 14:05 -------
Martin,

Kipi-plugins for KDE4 is able to convert RAW to PNG in 16 bits color depth.

Do not claim than you have a black hole image in this case because the target pictures is not corrected using a Color Management (like digiKam image editor do). dcraw produce a decoded linear image. It's different than 8 bits mode where gamma is automatically corrected.

You need to fix color/gamma by hand later using your prefered program witch support 16 bits color depth and color management : digiKam, cinepaint, or Krita.

Important : Gimp only support 8 bits color depth !

Guillaume, Marcel,

TIFF file format is supposed work properlly with 16 bits batch conversion. The code to write tiff image in 16 bits is very similar than digiKam DImg::TiffLoader... But it doesn't work. The image is completly broken on my computer. Of course, if i use digiKam image editor to save tiff in 16 bits all work fine!

After few investigations, i can said :

- In 8 bits color depth all work fine with TIFF.
- If i disable LZW tiff compression, all work fine.

Code from digiKam is in digikam/libs/dimg/loaders/tiffloader.cpp on method save().

Code of TIFF writer used by plugin is in kipi-plugins/common/libkipiplugins/kpwriteimage.cpp on method write2TIFF().

To have a propers tiff image with the plugin, just comments these lines in kpwriteimage.cpp :

TIFFSetField(tif, TIFFTAG_COMPRESSION,         COMPRESSION_ADOBE_DEFLATE);
TIFFSetField(tif, TIFFTAG_ZIPQUALITY,          9);
// NOTE : this tag values aren't defined in libtiff 3.6.1. '2' is PREDICTOR_HORIZONTAL.
//        Use horizontal differencing for images which are
//        likely to be continuous tone. The TIFF spec says that this
//        usually leads to better compression.
//        See this url for more details:
//        http://www.awaresystems.be/imaging/tiff/tifftags/predictor.html
TIFFSetField(tif, TIFFTAG_PREDICTOR,           2); 

... of course in this case the tiff file is huge (non-compressed). This is weird.

I don't know where is the difference between digiKam and kipi-plugins implementation. I suspect a problem with zlib witch is used to commpress image data. Perhaps something is wrong to link libkipiplugin shared library ?

Can you reproduce this problem on your computer ?

Gilles Caulier