What Size Should My Image Files Be?
What Size Should My Image Files Be?
A very gray area among many authors concerns image size. Often people will equate the size and apparent quality of an image on screen with the size of the file and assume that if it looks OK on screen, it will look OK when printed. That’s not necessarily the case.
The issue that comes up most often concerns photographs: Authors really want to use a specific photo, but aren’t clear with regard t0 the size (and more importantly the resolution) that photo file needs to be in order to be printed.
Specifications of the file determine the resolution, which will greatly affect the quality of the printed image.
The resolution of a digital image is measured in pixels, usually expressed as pixels per inch (PPI). For printing, the measurement refers to the dots of ink. That’s expressed as dots per inch (DPI).
The higher the PPI or DPI, the sharper the picture will be: There will be far more detail and the image will be clearer.
For high-quality printing, it’s generally advisable that the original file be 300 PPI.
The native size of this image is 6291 × 4139 pixels, or 20.97 × 13.797 inches. Those measurements are irrelevant since the image will be scaled down to a size suitable for a book. But the resolution will remain 300 PPI.
At Virtus, we recommend 300 PPI. The lowest we will generally accept is 150 PPI (which may be OK with some images, depending on the level of detail).
But it is always advisable to submit the highest resolution that’s available.
Another area of confusion (and one that’s understandable) concerns online versus offline. In general, what is viewed online is 72 PPI. This means that an image that’s displayed on screen and simply saved and printed will not look as good as it does online.
And saving that file (which will be 72 DPI) and increasing the resolution in a program such as Photoshop will neither address the problem nor actually increase the resolution of the file.
It’ll be a 300 PPI version of a 72 PPI file: It won’t look any better when printed, and may actually look worse.
(Compare this to a monaural audio recording: Saving that audio file in stereo won’t magically make it stereo: It’ll still be a mono file, with both the left and right sides identical.)
In terms of file type, JPEGs are the most popular format, especially for use online, but for high-resolution images to be printed, PNG or TIFF files are preferred. At Virtus, we recommend these options. JPEGs are compressed, which leads to some degradation in quality. PNG and TIFF files are lossless, meaning there is no degradation.
To cite another audio example, the ever-popular MP3 is a portable audio file that’s small enough to allow you to have thousands on your phone. It’s a compressed format, with inherently less information. A WAV file is CD quality and will always be a much larger file. Audiophiles prefer WAV (or even better FLAC) files to maintain the quality of the original audio file (which simply isn’t possible with an MP3, regardless of what you read elsewhere online).
Going back to your images, one point to keep in mind is that the higher the resolution, the larger the file size. The file size of the native version of the image used in this post is 15 MB (megabytes). This is pushing it in terms of trying to email the image. This is why the files in an art program are generally saved in a folder that is zipped then posted to a secure cloud storage site for download. (See the post “What is an Art Program?”.)
At Virtus, we provide authors with easy-to-follow guidelines for the submission of their art program.
Like this post? Follow Virtus Publishing on LinkedIn!