Publishing companies will have varying requirements and policies regarding how authors provide photos and illustrations. However, we will discuss some general guidelines here, the first of which is your publisher will most likely require your images to be in digital format (as opposed to snapshots, drawings, or other “hard-copy” formats). If you do not have your images in digital format, you will need to scan them. If you do not own a quality scanner, check to see if your publisher offers scanning services. If so, this is likely your best option since a publisher should be familiar with the image quality necessary for book printing. Other options include taking your images to be scanned at a local print shop or copy center that offers scanning services. If you use one of these options, make sure the establishment is capable of producing the image quality you need for your book.
For printed books, images should have a resolution of at least 300 DPI (600 DPI is better both for quality and more precise sizing). If you must scan your images, make sure the scanner used has the capability of scanning at this resolution.
If your images already exist in digital format, use photo-editing software (e.g., Adobe Photoshop) to check the resolution of each image. If lower than 300 DPI, your best option is to re-scan the original (non-digital) image at 300 or 600 DPI. If you do not have access to the original, use your photo-editing software to raise the resolution to 300 DPI. There is no significant advantage to having resolutions higher than 600 DPI. Resolutions higher than this result in a large file size, making the image difficult to work with and unnecessarily bloating your book’s file size.
Image File Type
One of the best file types for book images is JPEG (file extension of .jpg or, less commonly, .jpeg). This file type works for many kinds of images, including photographs and other images with smooth color variations. JPEG also supports the CMYK color profile used by most printers, and is a common file type supported by all or most scanners, digital cameras, and photo-editing software applications. There are a few key issues with JPEG files to be aware of:
- JPEG files have the ability to be compressed to varying degrees to control file size. The more a JPEG file is compressed (smaller file size), the lower the quality of the image. When saving book images in JPEG format, make sure you choose the lowest compression (highest quality) setting in your photo-editing application.
- JPEG files should not be repeatedly edited and saved. Each time the file is changed and saved, it is recompressed, causing a loss of data, and hence, a loss of quality. If you have a JPEG image that requires extensive editing (e.g., cropping, retouching, resizing), it is best to convert the file to the TIFF format (discussed below), complete all edits, and save only the final version as a JPEG file.
The JPEG format works for nearly all kinds of images, but the TIFF (file extension .tif or, less commonly, .tiff) file type is slightly better for line drawings and other images with sharper color transitions. Like JPEG, TIFF is widely supported by scanners and photo-editing tools and supports the CMYK profile. The biggest advantage TIFF offers over JPEG, though, is its ability to be edited and saved multiple times without any loss in image quality. One disadvantage is TIFF files are larger than those of the JPEG type.
Image Size (Dimensions)
You should provide digital images at least as large (i.e., physical width and height, not file size) as they will be in your final book. If your publisher needs to resize any of your images, there is less loss in quality associated with reducing image size as opposed to enlarging. If your source images, digital or non-digital, are smaller than you need, you have options to enlarge them while minimizing quality loss:
- If you have non-digital images and a quality scanner, enlarge the image using the scanner. Generally this will produce a better-quality enlargement than that produced by resizing with photo-editing software.
- If you have digital images, you may use photo-editing software, but make sure the software is high-quality or professional (e.g., Adobe Photoshop). Most free applications, such as those that come pre-installed on a computer or are bundled with a digital camera, cannot produce quality enlargements. If you don’t have a higher-end program, you should invest in one or check whether your publisher offers photo-editing services.
We will discuss the use of color in your book in the Color vs. B&W/Grayscale section, but here we will discuss the topic as it pertains to images. If your book is destined for printing, your publisher will most likely require any color images to be in CMYK format, and any non-color images to be in CMYK or Grayscale format. Before you worry yourself too much about this requirement, check to see if your publisher will convert your images to the correct color profile at little or no additional cost.
Computer screens display colors using the RGB (Red, Green, Blue) color profile, and computer applications also use this format. While many home and office color printers actually print in CMYK, they convert RGB colors from your computer applications to CMYK so there is no need for you to perform this additional step yourself. However, most book printers require images in either CMYK or Grayscale (for non-color images) format, and most ordinary photo-editing applications do not have the capability to convert from RGB to CMYK (although many do have the capability to save in Grayscale format).
If your publisher will not perform color-profile conversion for you, or will do so only at an exorbitant price, you may wish to invest in an application such as Adobe Photoshop that can output images in CMYK format.