JPEG File Size

Earlier this week, a client asked me whether a JPEG image of jewelry was high resolution even though the file size appeared to be small. Several factors determine the size of a JPEG file, and the number of pixels in the image is only one of them.

The JPEG format compresses images to reduce the size of the file for easier emailing or storage ... a ten megapixel image can easily be compressed into a two megabyte file or smaller. The amount of compression, though, can affect image quality because adjacent pixels with similar values are "averaged". More compression averages more pixels and can reduce the effective resolution of the image.

The characteristics of an image also affect JPEG file size. An image with large areas of similar color will compress to a much smaller file than an image with a lot of variation. As a result, images of sculpture and jewelry where there is a uniform background will usually have smaller files.

In the case of my client's image, it was high resolution but the file was small because the background behind the jewelry was a uniform black ... so the image was compressed more than usual with no loss in quality.