In practice, the RAW value that corresponds to middle grey is different for different cameras, even if normalized to the maximum and calculated in percent.
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The existing ISO 12232:2006 standard talks about how the out-of-camera JPEG should behave, but doesn’t mention the RAW. This becomes possible for the simple reason that “ISO light sensitivity” for RAW data isn’t defined in any way.
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Adobe DNG Converter set this tag to non-zero “hidden exposure compensation”.
The first, meanwhile (the original ORF), doesn’t contain this tag at all, but the Adobe converter “assumes” it.Ī careful reader, having looked at the names of the files in the screenshots, will know that the third shot was converted to DNG with the aid of digiKam, the second with Adobe DNG Converter (version 9.7).In the second file, it’s not zero (we’ll show what it is a little later).The third file (the brighter DNG) has the following written in this tag:.The difference is in the metadata! In particular, the effect above is controlled by the BaselineExposure metadata tag, present in DNG: We will answer this one without further ado. The RAW data is preserved and undistinguishable between the three, as we just saw in RawDigger, and yet… Why is this? Both DNG files result from converting the original ORF file (Figure 1. If we take the middle of the three samplers, it’s almost exactly middle grey on the first two files (the value = 119), while the third file (value = 162) has a brightness difference coefficient of 1.97, which constitutes nearly an entire photographic stop: (162/119)^2.2 ≈ 1.97, here we take the ratio to the power of 2.2 to un-do gamma, getting the linear values. Second samplers' values: for the original ORF (left), Adobe DNG (middle), digiKam DNG (right).