Today’s Question: How can I tell if an image is raw? I know that the file extension can be helpful to tell if a file is in raw format. Usually. But what if I do something like export a JPG file to DNG from Lightroom Classic? And then I import a different Canon raw capture as a DNG. How can I look at the two DNG files and determine which one is a true raw image?
Tim’s Quick Answer: I don’t know of any software that makes the task of identifying the source of a DNG file particularly easy or reliable. However, you can open a DNG file with a text editor and search for an indication that the file was converted from a different file type.
More Detail: With a proprietary raw capture format, you can essentially just tell from the file type that the file is indeed a raw capture. The same is not true for an Adobe DNG (Digital Negative) file.
A DNG could be an original raw capture, as a variety of cameras support raw captures saved directly as a DNG file. You can also convert a proprietary raw capture to the DNG format, with the option to embed the original raw capture in the DNG file if you’d like. Both of these would provide you with a file that could be considered a raw capture.
However, it is also possible to convert other image file formats to DNG. You could, for example, capture a JPEG image with a smartphone and then convert that JPEG image to a DNG file. This represents a DNG created from a non-raw source, meaning there is full color information for all pixels in the image, unlike most raw capture formats. This type of DNG file is referred to as a Linear DNG.
If you open a DNG file with a basic text editor on your computer, you can search for the text “converted”. With the software I’ve tested (which in this case only includes Adobe software), a DNG file that was converted from another file format will include text in metadata describing the conversion. For example, a JPEG I converted to DNG includes the text “converted from image/jpeg to image/dng, saved to new location”.
Viewing a DNG file this way isn’t the easiest task, and you need to be very careful not to make changes to any of the text and save the modified file, as that can corrupt the image.
If any readers are aware of software tools that streamline the process of determining the provenance of a DNG file, please let me know and I’ll be happy to share that information.