Output File Size

DOwnloaded the trial to check out and have an initial question:

Why are the resulting DNG files almost 3x larger than the originals? When I process NEF files in Lightroom and export as DNGs, those DNG files are roughly the same size as the NEFs.

Please note that the same is true for PureRaw.
Output files are “linear DNG” files, hence the size difference.

Copied from Adobe: Adobe Digital Negative Converter

  • Linear (demosaiced)
    The image data is stored in an interpolated (“demosaiced”) format. This option is useful if a camera’s particular mosaic pattern is not supported by a DNG reader. The default mosaic format maximizes the extent of data preserved. Mosaic image data can be converted to linear data, but the reverse is not possible.

PureRaw is a useful programme that has a lot of potential. I have also noted that DXO PureRaw produces DNG files three times the size of the original raw files.

I have understood the explanation given above that DXO Pure Raw Converts to linear DNG. However, users need to be given the option to have a smaller raw or Tiff file. IMHO this is a problem that needs to be fixed.

My CR3 files from my 90D are about 45 Mbt. If I convert these with Adobe DNG converter then the raw files with lossless compression are about 50 Mbt which is acceptable. DXO PureRaw produces raw files about 135 Mbt.

For example, DXO RawPrime could export to a tiff with lossless compression (LZW or zip). That would be better than a jpg. Or maybe the file can be exported to tiff and then back to the smaller non linear version of DNG.

Just my 2 cents worth.

Thank you for your hard work in developing this software.

Kind regards

Somebody may correct me.

DNG files are TIFF based files. They both contain RGB values: 3 channels per pixel.
RAW files do contain R,G,B values: 1 channel per pixel.
My Nikon D750 has 6016x4016 pixels. For simplicity the sensor has the same elements.
I shoot 12 bit RAW. The RAW image will be 6016x4016x12=289923072bit or divided by 8 36240384byte. or 34.56MB.
The 16 bit DNG/TIFF takes 2 byte per channel. That means 6016x4016x2x3=144961536byte or 138.25MB. NB: 16 bits.

Lineair DNG means no corrections to the demosaiced image has been done. This doesn’t have any influence on the amount of pixels.

From Adobe https://www.adobe.com/content/dam/acom/en/products/photoshop/pdfs/dng_spec_1.4.0.0.pdf
Under the tag compression I read that if compression has been used, it will be a JPG compression.

So what I would think that if the DNG file is not much bigger as the raw file, then either 8 bits has been used or a JPG compression has been used or both. If so, I wonder why I had to shoot in RAW??


Please see recent reply to a post by someone regarding output tif file. Thanks

Thank you George for this explanation. Its clearer after seeing the math.

However it must be theoretically possible for DXO to output to a smaller tiff in a future release. It will be helpful if users have this option. Not everyone wants a massive DNG.

Here is what I have found.

1- Original CR3 File 46 Mbt
2- Converted by Adobe DNG Converter 50 Mbt (Lossless)
3- CR3 converted to DNG by DXO PureRaw 134 Mbt
4- 134 Mbt DNG From DXO opened as 8 bit rgb PSD 85 Mbt
5- Same PSD saved as 8 bit RGB TIFF (LZW Lossless) 39 Mbt

Users could be given the option of choosing which modules of DXO PureRaw to apply. If de-mosaicing is not required, then maybe it will be possible to get a smaller DNG or Tiff.

Kind regards

Keep in mind that the Adobe DNG converter is creating DNG files with no edits while PureRAW is adding corrections for Chromatic Aberration, Lens Distortion, Vignetting, Lens Sharpness and Noise Reduction. Perhaps an increase in size by 3 times is excessive, but I would expect the output to be much larger than from the DNG Converter.


Strange things with Adobe DNG converter.
NEF file D750 6016x4016 30.5MB
Adobe DNG converter .dng file 1024x684 27.6MB, 24 bit color depth. When opened in IrfanView it shows 1024x684B. When opened in Photolab it shows 6016x4016.

Chris, have a look at the properties of your file from the Adobe DNG converter.


It seems that the properties are referring to the embedded jpg.
To me the only explanation for the smaller file size is that it is stored in the original, not de-mosaiced, structure with the camera parameters in a general structured form.
When I select a embedded jpg in full size, the file size is about the original size.


@George, I just checked Adobe DNG Converter output at different settings. This is what I got with a few images of different dimensions and size:

Each of the four blocks of images go along with the following rule:

  • Original file (white background vs blue background of DNG files)
  • DNG output with DNGC set to default conversion settings
  • DNG output with DNGC set to custom (version 1.4) setting, uncompressed
  • DNG output with DNGC set to custom (version 1.4) setting, compressed
  • DNG output with DNGC set to custom (version 1.4) setting, linear, uncompressed
  • DNG output with DNGC set to custom (version 1.4) setting, linear, compressed

DNG output files can be smaller than the original file or considerably larger.
DPL 4 (current release) accepted+processed all DNG files without hesitation.
DPR 1 (current release) accepted+processed all except the linear DNG files (expected)

DPR Output size per file is the same, no matter what type and size the file image had,
the example image 20130220-5160 turns out to have a size of 99 MB, which is close to the 94 MB of the linear compressed file written by Adobe DNG Converter but still about three times the size of the original .cr2 file.

My lessons learned: If drive space matters, don’t use DPR - or get more drive space.

What I see that when no linear RGB is involved that then just the CFA from the original RAW is copied and the parameters rearranged in a standardized order. Just a guess.
The difference in size between the original and the …-std.dng is caused by the smaller embedded jpg. When you choice a full size embedded jpg the file sizes are nearly or exactly the same.

The addition ad means adobe.