Thanks, Godfrey ... Very useful information ...
Shel "You meet the nicest people with a Pentax" > [Original Message] > From: Godfrey DiGiorgi > > When converting PEF files to DNG, the converted file is roughly 50% > > of the > > original. That suggests that some, perhaps a lot, of information > > in the > > original file is discarded. What's lost? > > Nothing, with DNG Converter v3.1 and up. > > > When working with DNG and PEF files, and converting them to PSD or > > TIFF > > files after going through the RAW converter, the file sizes (for > > DNG and > > PEF "originals") are about the same size, and I see no difference > > in the > > results obtained from either format. How is it that the DNG, which is > > about 1/2 the size of a PEF, and the PEF, yield similar sized files > > when > > converted? > > > > All this suggests that the PEF, and I suppose other RAW format files, > > contain a lot of unnecessary information. Given that the results > > from a > > PEF and a DNG file are identical, is there really any reason to > > save the > > PEF file? > > A Pentax RAW format file is essentially a Tagged Image File Format > (TIFF) file with a Pentax specific data layout. TIFF is simply a > container format standard which is generic and broad enough in > definition to store all kinds of image data. Rendered RGB files > stored in TIFF format follow a widely accepted protocol standard for > what the tags and data elements mean in terms of data organization; > PEF files use the format but use their own sets of tags to determine > the component contents. > > What's in a PEF file? > > - All the image and camera metadata (exposure settings, EXIF format > data, some image and camera identification data, and a few bits and > pieces of other data in proprietary format that Pentax feels they > want to stuff in there for present and future use). > > - The sensor data itself. > > - At least two JPEG renderings ... the thumbnail used for whole image > display on the LCD, a JPEG preview rendering for sure, and (I think) > a full resolution, high compression JPEG rendering used on the LCD > for when you zoom and scroll around. > > DNG files also adhere to TIFF format protocol, but DNG is an openly > distributed format so all the components have easily discoverable > tags and organization. It was conceived of as a modifiable container > format so developers can use and modify the contents easily. What > does it contain? Well, pretty much the same thing that PEF files > contain (metadata, JPEG preview and thumbnail, sensor data). It can > also contain an encapsulated PEF file if you turn on that option. > > Why are DNG files smaller? > - Pentax applies no compression to the sensor data. Because the > compression is bit-for-bit lossless, no information is lost. > - The DNG Converter applies lossless compression and can save up to > 30-40% on size. > - Pentax JPEG preview files are somewhat large, the DNG Converter > produces a better quality JPEG at smaller > size. > > All RAW format files contain some metadata that could be considered > "unnecessary", but the proportion of such unnecessary data to sensor > data content makes that insignificant. They might have 100-500K worth > of metadata, the sensor data is much much larger than that. > Losslessly compressing the sensor data is the key to their smaller size. > > Why are PSD and TIFF RGB files the same size when made from PEF and > DNG files? > Should be obvious now, but basically since the DNG and PEF files > contain the same information, the RGB rendering from either will also > contain the same information and be the same size when constructed by > Photoshop. > > Is there really a reason to save the PEF file? > There are arguments for archiving one, the other or both. Some > argument points to DNG being an open standard and therefore having a > better chance at 'archival' usability than PEF files (which is true). > Some arguments suggest that you can always derive a DNG from a PEF, > but cannot do the opposite, so you should save the PEF (logical). DNG > Converter includes the ability I mentioned to embed the PEF file INTO > the DNG (and similar capability to extract it), so that's another way > to archive both, but it makes the DNG files larger. > > Personally, since the DNG Converter is now in its third revision and > I never use the Pentax tools for RAW conversion (which are the only > tools that can use the Pentax private, proprietary data in the > makernotes metadata), I'm beginning to move over to the notion that I > should archive only the DNGs and to heck with the PEFs after I get > them out of the camera. But I still linger on the notion that the PEF > output is the actual original file that I can always go back to, so I > am archiving PEFs as yet and working with DNGs. > > Godfrey
