Today’s Question: I’m still using Photoshop CS6 because I did not want the subscription option [Photoshop CC]. Raw files for my Canon 5D Mk III are 27MB in size, but become 24MB when I convert to Adobe DNG [Digital Negative]. Am I doing something wrong? Is the raw file still the same? Or am I losing critical data on conversion?
Tim’s Quick Answer: The smaller file sizes you’re seeing are due to the fact that the Adobe DNG file format employs lossless compression to reduce the file size. None of the original capture data is altered as part of this process, other than any “special” metadata that might only be supported by software from the camera manufacturer.
More Detail: As a general rule you can expect a raw capture converted to an Adobe DNG file to have a file size that is about 20% smaller than the original capture file. As noted above, this is due to lossless compression that will not alter the original capture data for the image. You will not lose any image quality or detail as part of the conversion to Adobe DNG.
It is worth noting, however, that any “special features” that might be supported by the software from your camera manufacturer would be lost as part of this conversion process.
For example, recent models of Canon cameras include a “dual pixel” feature that can only be leveraged through the use of Canon’s software with the original raw capture. Similarly, most recent Nikon camera models support an “Active D-Lighting” feature that requires Nikon software (and the original capture format) to make use of.
Other than these “special” features (that are not supported by Adobe Lightroom, Adobe Camera Raw, or Photoshop, for example), there is no impact on your original captures caused by the conversion to the Adobe DNG format. In particular, the smaller file size caused by lossless compression for the DNG file need not be of any concern either, as it is actually one of the benefits of the DNG format.