Today’s Question: We had pictures taken at our 50th and the photographer provided them in PNG file format. What is it and how do I convert to NEF or JPG?
Tim’s Quick Answer: The Portable Network Graphics (PNG) image format is actually a very good image format that I consider to be (in most respects) better than the JPEG image format. You could certainly use a variety of different software tools to create a JPEG image based on the PNG, but you may not need to. And there is no way to convert an image file such as PNG or JPEG to a RAW capture format such as Nikon NEF.
More Detail: The PNG image format supports lossless image compression and 16-bit per channel data, which is a considerable advantage in terms of image quality compared to JPEG image files. Frankly, the only real reason to use JPEG instead of PNG is to obtain a smaller file size through the lossy compression employed by the JPEG image format, which does degrade image quality to some extent.
I’m not really sure why the JPEG image format managed to gain wider adoption than the PNG file format. Part of the issue was a lack of support for the PNG format in various software applications. In fact, Adobe Lightroom didn’t even support the PNG format until version 5.
I would suggest keeping the PNG files as your “original” image format, creating other image file types only as you need them. You can use Lightroom to export a copy of the PNG files as JPEG (or other format) images, or use Photoshop or other software to save a copy of the image in a different format. But in most scenarios that probably won’t be necessary, and the PNG files will provide you with a good source in terms of overall image quality.
You could, of course, contact the photographer to see if they were using RAW capture, and if so ask if it would be possible to obtain the original RAW captures for at least your favorite images. But in many cases a commercial photographer will be reluctant to provide the RAW captures, preferring to provide only processed images to the client.