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Subject: Re: OpenRAW article: "DNG is not the answer"!

nunatak, what is the contradiction between "being a totally self contained format" and "it's processor side dependent"?


Let's take something so trivial that surely no one would have a problem with it. Suppose a raw file contains not only the raw image data, but also parameters that state the dimensions of the sensor, eg. 3040 x 2024, or 4008 x 5344.

Now suppose some raw converters can only allocate space for up to 10 megapixels for some reason. So they can handle the former (Pentax DL) but not the latter (Leaf Aptus 22). So they can handle some cameras but not others. Is that the fault of the raw format? No, of course not!

Suppose a raw file describes the colour filter array configuration. For example (over simplifying):
colour1 colour2
colour3 colour4
Now suppose a raw converter can only handle:
Blue Green
Green Red
This will work for the D1, D1X, D50, D70, D70s, etc. It would handle these if it ignored the parameter or if it only handled that particular value. But - not the D200.
So, suppose the raw converter added support for all varieties of Bayer configuration. It would support lots more cameras, including the D200.
But - not the Sony F828, which is:
Red Cyan
Green Blue
For that, the raw converter needs to be able to handle at least 4 colours.

And so on. Whether a raw converter can support particular cameras becomes a matter of how many of the DNG parameters it has been coded to support. In each of the above cases, DNG is "a totally self contained format" but support is "processor side dependent". It relies on a coder bothering to write the required code, probably depending on the return on investment for the effort of writing that bit of code.

DNG is self-contained. It is possible to write code that handles every combination of parameters. ACR from 2.4 onwards does a plausible job, although I don't know how many compromises it had to make. Other raw converters haven't done such a comprehensive job. No doubt they will improve steadily - without having to change DNG.

Don't be misled by the tales that suppliers of raw converters give for not supporting DNG fully. Just remember that ACR 2.4 supports more than 50 cameras via the DNG route that it doesn't support via the native raw route. No one who claims that DNG isn't self-contained has an explanation for that!


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