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File size after IXT -- huge DNGs?
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p.1 #1 · p.1 #1 · File size after IXT -- huge DNGs?

The RAFs coming out of my X-T2 are around 25 MB. After running them through IXT (Iridient X Transformer), I'm ending up with DNGs around 62 to 67 MB; I have seen some that are larger -- as much as 86 MB. For Bit Depth I'm using "Same as original RAW", and I've checked "Use lossless compression".

Is this normal? Brian's documentation suggests the DNG should be about the same size as the RAF. This is a huge increase in file size!

I'll check with him too, but I'm curious if others are seeing this. I just reported an issue yesterday that he's never heard of (occasionally IXT simply skips a file I asked it to import). So before I go to him with this one I'm checking to see if it's just me again!

Aug 28, 2017 at 10:54 PM
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p.1 #2 · p.1 #2 · File size after IXT -- huge DNGs?

Seems about right - the compressed DNGs aren't much bigger than the uncompressed RAF files - you can always save a few MB by eliminating the jpeg preview.

Here is Brian's explanation in response to a post on DPReview:

The main reason the DNG file will be larger (assuming same bit depth) is that the processed DNG will contain full color, 3 channel RGB data. The original RAF image will contain just a single color filter array (CFA either Bayer or X-Trans) channel, sometimes termed "mosaic" data. The critical RAW processing stage interpolates or demosaics the sensor data into full color image information and in doing so the image becomes 3x larger.

Lossless compression will definitely help reduce DNG file size (typically 30-40%). There are also bit depth options available (8 or 10 bits/ch) that can even result in a final DNG that is often smaller than the original RAF, but these formats are "lossy" due to the bit depth reduction and some of the image information will be lost. Most RAF images are natively 12 or 14 bits/channel.

Aug 29, 2017 at 12:20 PM
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p.1 #3 · p.1 #3 · File size after IXT -- huge DNGs?

Thanks for confirming.

Brian got back to me too. His explanation in an email (which he gave me permission to post here) adds a bit more info. I also asked about cameras that shoot "natively" in DNG and why the files were smaller. That might be useful to know too so I pasted that in here as well.

On the original question:

"Assuming similar bit depth and compression is used for the RAF and DNG, the DNG from X-Transformer should be about 3x the file size. The reason for this is that the core RAW processing (demosaic) applied by Iridient X-Transformer interpolates the single plane of sensor color filter array (or CFA) information into a full 3 channels of R,G,B information. This processing necessarily results in 3x the image information. Some DNG converters may allow for a simple format conversion from RAF to DNG without any interpolation (demosaic), but as the primary feature of Iridient X-Transformer is the demosaic processing this doesn't make sense for X-Transformer.

By using reduced bit depth options you can can reduce the final file size significantly, but these options are lossy. Some camera manufacturers that offer reduced bit depth RAW modes (such as Nikon, Leica, etc) sometimes refer to this a 'virtually lossless'."

And on why my Ricoh GR had much tinier DNG files (taking into account it was a 16 MP rather than 24 MP sensor):

"Most RAW images in-camera store the direct color filter array (CFA) image data from the sensor with no interpolation (or demosaic) at all. The Ricoh GR is a Bayer camera and stores the DNG as non-interpolated CFA data. This would be equivalent to the RAF image information stored by the Fujifilm camera's, but X-Trans simply uses a different CFA layout. The image data is still a single plane of CFA information, the pattern is just different between Bayer and X-Trans, but both use a monochrome sensor covered by a color filter array.

After interpolation (or demosaic) the Ricoh GR images would become 3x the size of the in-camera DNG too."

Aug 29, 2017 at 12:38 PM

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