Why use DNG file format?

Question

I have a few questions about using DNG file format. When would I save a file as DNG instead of JPEG or TIFF file? Why? And how is the extensible metadata platform (XMB) related to the DNG file format?

Answer 1

DNG is the cross platform version of a RAW file, RAW file are specific to a manufacturer and even to a specific model of camera, DNG files are not.



A few manufacturers such as Pentax allow you to save your RAW files in this DNG format in camera, the big advantage is that any version of Photoshop can open them, you don't need to have the version of PS that your camera would otherwise need.



The RAW file in any format is just the image data and is read only, you can't write to it, it's impossible to overwrite a RAW file.



The XMP (not XMB) file is the file that stores any editing changes you make, there is one associated with every RAW file. If you go to the View menu in Bridge and select the 'Show Hidden Files' the XMP file will appear alongside any RAW file. If you delete this file you just delete any changes you have made to the file the original image data is in the RAW file. It's a quick way to erase changes when you get it wrong. A new XMP file will be generated when you open the Raw image again.



You can associate an XMP file to any image file no matter what it's format, even Jpeg. By highlighting an image file in Bridge, right clicking and select 'Open in Raw Converter' in the drop down menu. PS will treat the Jpeg (or any other image format) as if it was a RAW file and store any changes made to the image in the XMP file. Editing in this way will always preserve the data in the image file.



Chris

Answer 2

Generally you wouldn't save as DNG instead of JPG or TIFF -- you'd save a *copy* of RAW files as DNG. The reason is that DNG is an open format; anybody can get and read the specifications for it, and easily write software to read/convert/load images in DNG format. That's not the case with RAW file formats, which are proprietary to manufacturers, and which are often most certainly NOT public. If you want to have a little insurance that your RAW files will be readable 10 or 20 years from now, saving a copy in DNG format is one good way to do that.



I think you mean XMP instead of XMB. XMP files are "sidecar" files, that go along with RAW or DNG files; they contain "development" information -- what settings were used to convert a RAW or DNG file to a normal RGB image that can be viewed, edited, or saved in another format. This data is saved in an external XMP file instead of in the original RAW or DNG file so that the original file isn't changed in any way.



peace.

Answer 3

If you need more details for editing in the computer, use it. If you don't know how to, then don't. It's that simple.