M8 vs D200 DNG files

[Stan Raucher]

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I did some testing with conversion of the M8 dng file from digital outback to tiff files versus conversion of raw files from my Nikon D200. Here are the results.

 

The M8 dng file from Digital Outback is 10.6 Mb. When I open this dng file in CS2 using Adobe Camera Raw with auto turn off and no other adjustments and save it in PSCS2 as an uncompressed tif file the size is 60 Mb.

 

A typical nef file from my D200 is around 16 Mb. If I convert a typical D200 nef file to a dng file using Adobe Digital Negative Converter (ver 3.4x89 with preference JPEG Preview none, Compressed lossless, Preserve Raw image, Don’t embed original), the resulting dng files are typically around 9 Mb. When I open either an original D200 nef file or the corresponding converted D200 dng file in ACR and save it in PSCS2 as an uncompressed tif file the resulting files are indistinguishable (overall appearance, file size, information on the histogram palate) and the file size is typically around 37 Mb.

 

I have repeated the above conversions with similar results on a dozen other M8 dng files (firmware ver 1.06) that I shot myself at a Leica demo day on Saturday at Kenmore Camera in Seattle. Those files also started life as 10 Mb dng files and ended up as 60 Mb uncompressed tiff files by the procedure outlined above.

 

Although the M8 dng files that I converted are different images than those from my D200 nef files, it seem like the M8 dng files somehow hold more information as reflected in the larger size of the resulting tif files (60Mb for M8 vs 37 Mb for D200). This is most probably because M8 dng files are 16-bit whereas Nikon nef files are only 14-bit.

 

Here is one more curious result from the M8 dng files which occurs for both the Digital Outback dng file and the M8 dng files that I shot myself. If an original dng file is processed with Adobe DNG Converter (ver 3.4x89 with preference JPEG Preview none, Compressed lossless, Preserve Raw image, Don’t embed original), the resulting dng file is only around 7 Mb! If that 7Mb compressed dng file is then opened in ACR and saved in PSCS2 as an uncompressed tiff file it is indistinguishable (overall appearance, file size, information on the histogram palate) from the tiff file produced by the original M8 dng file. Maybe that’s not surprising since the conversion is designated as “lossless”.

 

So how can Leica get 10Mb of 16-bit data into a 10Mb dng file? My guess is that they have developed some extremely powerful lossless compression algorithms for writing the original dng files in the camera. It also is interesting that these dng files can be further compressed by about 30% in a lossless manner with Adobe DNG Converter.

 

I’ll post my general impressions of the hour a spent with the M8 later this week.

 

Cheers,

 

Stan

 

BTW, I find it highly unlikely that the Leica dng files are 8-bit rather than 16-bit as purported in some threads. Would any car company launch a new car that it was staking its reputation on claiming that it had 8-cylinders when it really only had 4? Leica knows people will be looking under the hood.

[scott kirkpatrick]

Your results on the M8 files make sense. The raw file contains one byte (8 bits) per pixel, which is obtained by taking the square root of the original pixel data. Expanding it to a TIFF, uncompressed, you obtain 3 words (RGB, each 2 bytes) per pixel, or 60 MB. DNG with compression eliminates duplication in the original data, so it produces a file smaller than the original 10 MB, 7MB in your case, although this result will vary.

 

Expanding the Nikon files involves different steps, and there are probably different instructions coded in the NEFs, so I am not sure what one can conclude from the comparison.

 

The information about what is in an M8 file comes from Andrej Kolev, who has written RAW development software. He can open M8 files and produce the same picture as everyone else sees, and what he finds is a sensible procedure, known as "companding" in the image and audio processing world. Several of us have tried manipulating the tone curve of M8 files and DMR files modified to use this 8bit sampling, without seeing any bad behavior.

 

It does seem that Leica's marketing folks got a little carried away, and are probably embarassed now.

 

scott

[Barry Pearson]

The raw file contains one byte (8 bits) per pixel, which is obtained by taking the square root of the original pixel data.

 

The DNG file contains a look-up table for use by the raw converter to convert each byte back to a linear value. Here are a few entries from it:

LinearizationTable: 256 entries

Table [0] = 0

Table [1] = 0

Table [2] = 1

Table [3] = 2

Table [4] = 4

Table [5] = 6

Table [6] = 9

Table [7] = 12

Table [8] = 16

Table [9] = 20

....

Table [40] = 400

Table [41] = 420

Table [42] = 441

Table [43] = 462

Table [44] = 484

Table [45] = 506

....

Table [97] = 2352

Table [98] = 2401

Table [99] = 2450

 

These are the results of squaring each byte and dividing it by 4. Whatever the values started out as in the camera, they appear to get mapped onto 14-bit values for use by the raw converter. I don't know whether this makes much difference in practice.