Why does converting RAW files to DNG make them much smaller, and does it reduce quality?
Asked 6/24/2013
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When I convert my camera RAW files to DNG, the file size drops a lot—for example from about 30 MB to 8.5 MB. Does this mean Photoshop/Adobe is shrinking the image or reducing quality? Is there a way to keep the original data size, and should I import as the original RAW instead of using “Copy as DNG”?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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On the import tab choose "Copy" instead of "Copy as DNG", then you will retain the large data amount. One of the benefits of using DNG is that it uses less space. But normally it is only a 20% improvement.
It would be helpful to know your camera model, so we can see waht raw format it is (compression or not, number of previews, etc..
The raws contains previews. Canon uses half resolution previews (resulting in 1/4 the size of it) while Nikon uses full resolution (but I dont know if they compress it harder). DNG may use something else (or not have a preview at all in your case). A preview can easily be 2-4Mb and sometime is it bigger than the raw data if it is high quality because it stores the image as RGB data, while the raw is basically a greyscale image (bayer pattern).
You can tweak DNG settings in LR: http://lightroomsecrets.com/2012/03/lightroom-4-tip-new-dng-options/
Note that most of the options will affect your file size:
- Embed raw file: your end result will be larger than the original
- Preview Size: You have some control of the output size.
- Lossy Compression: This is just wrong! You might actually have this one active.
- Embed fast load data (V7.1) - Larger output file
Originally by user11455. Source · Licensed CC BY-SA 4.0
user11455
13y ago
0
Generated from our catalog & community — verify before relying on it.
A much smaller DNG file does not automatically mean image quality was reduced. RAW files often contain extra data besides the sensor data itself, such as embedded JPEG previews, metadata, and camera-specific information. Converting to DNG can remove or recompress some of that extra data, which reduces file size.
In many cases, DNG saves space while preserving the useful raw image data. The large size drop you’re seeing may be due to differences in embedded previews or conversion settings, not necessarily loss of image quality.
If you want to preserve the original manufacturer RAW exactly as shot, import using the original file format rather than “Copy as DNG.” Also check your DNG conversion settings, because some workflows could save a different bit depth or preview option. Testing with Adobe’s standalone DNG Converter or comparing conversion settings may help confirm what’s happening.
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AI13y ago
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