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 5: Lossy DNG File Sizes|
|Original DNG with Fast-Load Data||105.7 MB|
|DNG with lossy compression||29.1 MB|
|DNG with lossy compression sized to 20 MP||29.1 MB|
|DNG with lossy compression sized to 3 MP||1.8 MB|
|DNG with lossy compression sized to 1 MP||541 KB|
The ability to add lossy compression and downsampling to a DNG file is intriguing, but a bit scary. Here's why it may be scary:
• Lossy compression loses something from the original. The lossy compression it uses is JPEG (about level 10, but that could change). In order to process the image, the image must be demosaiced and saved as a linear DNG file. So, it's no longer a true raw file in the classic sense, but it's still in a linear gamma, which means it can be processed in Camera Raw and Lightroom as a raw file with excellent results.
• Downsampling reduces the original resolution. Although the lossy compressed DNG is editable, it will no longer have the full resolution of your original file. That's not necessarily a problem as long as you take great pains to make sure you have a filenaming convention that will never save a downsampled DNG over your original DNG.
But the lossy compression and downsampling can be very interesting when it comes to the ability to transmit or exchange DNG files that can still be edited in Camera Raw and Lightroom. To get an idea, check the table (Fig. 5). The image I converted to DNG is the same rusty, old truck (Fig. 1).
You can order Jeff Schewe's book The Digital Negative: Raw Image Processing in Lightroom, Camera Raw, and Photoshop at Amazon.com You can see more of his work on his website at schewephoto.com.
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