Today’s Question: Occasionally, I attach a screen grab to an email, usually PNGs directly from my Mac’s screen-grab commands. In one example the PNG’s file size is over 860KB versus the JPG version at 208KB. Are PNGs always so big, at about four times the size of equivalent JPGs?
Tim’s Quick Answer: PNG (Portable Network Graphics) files will generally be considerably larger than JPEG (Joint Photographic Experts Group) images, because PNG images use lossless compression compared to lossy compression for JPEGs. The specific results will vary depending on the image in question, but when file size is the priority the JPEG format is preferred over PNG.
More Detail: When sharing images, the JPEG file format is a popular option because it enables you to achieve relatively small file sizes. This small file size is achieved due to lossy compression, meaning some degree of image quality may be lost even at a high quality setting.
By comparison, the PNG file format uses lossless compression. As a result, image quality is preserved at the cost of a larger file size.
Of course, at a high quality setting the JPEG image will generally appear to have quality that is nearly the same as the same image saved as a PNG file. Therefore, the JPEG file format is generally superior for sharing images where file size is a concern, such as for online sharing.
In theory the PNG format would be preferred when image quality is the priority. However, in those cases it might also make sense to instead use the TIFF file format. The main reason I consider the PNG format to be important is that it supports transparency in the image. This isn’t generally a necessity for a photographic workflow, but for certain uses (such as in digital slideshows, on web pages, or in videos) that feature can be helpful.