2009.02.17 06:00 "Re: [Tiff] DNG question", by Gordon Wetzstein

Hey guys,

thanks for the answers. I had a look at dcraw, which is a great tool, but I'm working on some de-mosaicking algorithms, so I need the CFA data. There is some sample code for a simple c DNG exporter (elphel_dng.c), which uses different TIFF

directories to store the thumbnail and the raw data. Unfortunately, my DNG files only have a single TIFF directory when I open them. I can extract the RAW data with dcraw, but the code is somewhat cryptic, so I don't quite understand how to access it. Since I use the Adobe DNG converter to create the files from various different SLR cameras, I can just set the compression to none, so that shouldn't be a problem.

I saw that Dave Coffin has a patch for libTIFF 3.8.2 on his website, but I'm using Windows XP and don't quite know how to apply that patch to my libTIFF. Maybe I'll give that another shot.

I also had a look at the DNG SDK, but it seems huge I would like to keep my stuff as simple as possible.

Thanks for your help.

Gordon

On Mon, Feb 16, 2009 at 8:53 PM, Chris Cox <ccox@adobe.com> wrote:

You might be better off using the DNG SDK instead of LibTIFF.

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From: tiff-bounces@lists.maptools.org [tiff-bounces@lists.maptools.org] On Behalf Of Gordon Wetzstein [gordon.wetzstein@gmail.com]

Sorry for another newbie question, but I'm trying to read DNG files with libTIFF 3.8.2.

I have converted my Nikon RAW files to DNG using the Adobe DNG converter. dcraw can correctly read the files, so they should be fine. Unfortunately, I cannot access the RAW data in the file from my program.

If I just open the TIFF file and read the tags, I only access the thumbnail, because the image size is smaller and I have an RGB image. I want the RAW mosaic data, however. Calling 'TIFFReadDirectory' until it returns 0 tells me that there is only one subfile in the TIFF, so no need to bother trying to change the TIFF directory.

I also tried to get a subimage with:

uint16 numSubimages;
uint32 subimageOffset[256];

TIFFGetField(tif, TIFFTAG_SUBIFD, &numSubimages, &subimageOffset );

numSubimages is always 1. Does that mean that there is one more subimage that I can access via TIFFSetSubDirectory(tif, subimageOffset[0]) or does it mean that there is only the thumbnail? If the latter is the case, how can I access the RAW data?

Any help is highly appreciated.