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Tuesday, February 26, 2013

DNG File Format & DNG Converter

In this excerpt from his book, digital master photographer and Photoshop Alpha-tester Jeff Schewe demystifies the DNG format for today and for the future

This Article Features Photo Zoom

Figure 3: The DNG Converter Preferences dialog box
Compare that to using the original Phase One IIQ file. If the image adjustments are saved to an XMP file (the text-based sidecar file that Camera Raw or Lightroom uses instead of trying to write into an undocumented raw file format), that text file is only 200 KB. So, 100+ MB versus 200 KB...you do the math.

On the other hand, when considering long-term digital conservation and preservation, things are a bit bleak (see the "Digital Image Preservation" sidebar).

The Adobe DNG Converter
Regardless of where or when you decide to convert raw files to DNG, I need to point out that the DNG file format is advancing (as of early 2012, it's at DNG spec version 1.4). The free Adobe DNG Converter (Fig. 2) and DNG conversion in Camera Raw 7.x and Lightroom 4.x offers some new and interesting features and functions.

Using the DNG Converter is pretty simple. You select the folder that contains the original raw files, select the folder where you want to save the DNG files, decide if you want to rename those DNG files (by default a DNG file extension is appended to the original filenames to prevent overwriting your originals), and then set the DNG Converter Preferences (Fig. 3). Both Camera Raw 7.x and Lightroom 4.x also contain the same basic functionality and options of saving DNGs. Here's a little tip: When using the DNG Converter, remember that it's designed to batch-process folders of raw files, not individual files.

Figure 4 (left to right): The Compatibility drop-down menu; the Image Size downsampling drop-down menu; the Custom DNG Compatibility dialog box

The preferences you set for DNG conversion are important to consider. If you're trying to convert to DNG for older software, you'll need to have the correct compatibility settings. New to DNG specification 1.4 is the ability to create what's called Fast Load Data. Checking this option stores additional preview data in the DNG file. This can speed the loading of images in Camera Raw and the Lightroom Develop module. It will increase the size of the DNG slightly, but it's a useful trade-off. However, it should be noted that third-party applications that claim DNG compatibility might not support DNGs with Fast Load Data.


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