DNG as Raw Capture


Today’s Question: You referred to a DNG file as a raw capture, but I thought DNG was something that you converted a raw capture to as an alternative. What is it exactly that makes a raw capture “raw”?

Tim’s Quick Answer: A raw capture is a file that contains the data gathered by the image sensor in a digital camera, which generally means a file that contains image data that has not been demosaiced. An Adobe DNG (Digital Negative) file created by a camera or created by converting a raw capture to DNG could also be considered a raw file.

More Detail: Using raw capture helps ensure optimal image quality both by avoiding alteration of the original capture data and maintaining high-bit data. I therefore highly recommend using the raw capture format in your camera (if available) rather than other options such as JPEG capture. Using Adobe DNG in supported cameras qualifies as being a raw capture in this context.

Part of what makes a raw (including DNG) capture “raw” is that the original capture data is not processed. Most digital cameras use an image sensor that does not capture full color for all pixels. For example, with a Bayer pattern image sensor for every four photo sites (pixels) on the image sensor there will be one red pixel, two green pixels, and one blue pixel.

When the raw capture is processed the image data is interpolated to calculate the “missing” color values for each pixel. A non-raw image format (such as JPEG or TIFF) is demosaiced, meaning the full-color pixel values have been calculated.

Based on all this, if your camera offers a DNG capture option instead of or in addition to a proprietary raw capture format, I would feel perfectly comfortable making use of DNG as a raw capture format. However, if the camera also offers a proprietary capture format, it is important to note that you could lose access to certain camera-specific features that are only available when using the software from the camera manufacturer to process a proprietary raw capture.