Estimated reading time: 10 minutes

1. How big should images be to look good when printed?

The file size of your images can indicate the quality of an image regarding size and resolution. If your image has a small file size, it means that your image will likely print at a low resolution, meaning that it will look pixelated or blurry. Trying to force the image to span a whole page would make it pixelated and blurry.

Usually, images with enough quality to print need to be at least 1MB (1,000 KB). This again depends on the size that you want the image to be, as bigger images will need to have a higher resolution and will have more KB or MB. It’s always best to supply your publisher with as big of image files as you can. There are a few ways to ensure you do this, but we’ll discuss that a little later.

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2. Some information about “dots per inch” (DPI) for image publishing

Dots per inch or DPI refers to how many dots of ink per inch a printer will put in an image when printing. So, the more dots your image has, the higher the quality when reproduced. This also means that the less dots your image has, the lower the quality of the image when reproduced.

When printing, your images need to be 300 DPI to keep their quality and reproduce well. With this in mind, you must be cautious when sourcing images from the internet. Most images online (unless you download them properly from stock websites, etc.) are set at 72 DPI, thus they will not print at a high quality. Let your publisher know that you have taken images from the internet and keep the URL of these images so your designer can check the size and quality, or so that they can more easily find another alternative at a higher resolution.

For screen publishing (i.e. for eBooks and other digital publishing mediums), 72 DPI works fine as this is the standard DPI for screens. It’s still best to let your publisher know about any images sourced from the internet, however, as copyright infringement is a possibility.

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3. Colour modes: CMYK vs. RGB

You may or may not be unfamiliar with what “CMYK” and “RGB” means and how it relates to image publishing, so we’ll go through everything starting at the basics. CMYK and RGB are both acronyms of the colours that they use to make up the colours in an image. They are both different modes of colour that are best used for different things.

The acronyms are as follows:

Visual representation of the difference between CMYK and RGB colour modes

3.1 What colour mode should I use for print image publishing?

With advances in technology, the answer to “what colour mode should I use for printing” has changed. CMYK was once the only option for printed images as the inks that printers used was cyan, magenta, yellow, and black. Now, however, it depends on which printing press you use. CMYK is still best when using offset printing, while RGB is best when using digital printing. Make sure to talk to your designer and publisher to figure out the best printing solution for your publishing project.

3.2 Colour modes and DPI

The way that traditional printers produce images is by nesting dots of different colours together to make other colours. When offset printing, the printer will mix cyan, magenta, yellow, and black together in different ways to create the colours in your image. On the other hand, when digital printing, the printer will mix red, green, and blue.

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4. What are the different file types for images?

Depending on how you are looking to distribute your book (whether it is meant to be an eBook or a print book), there are different file types to understand for image publishing.

4.1 Preferred files for print image publishing

• TIFF: A great alternative to Photoshop files (PSD). This file type is compatible with transparent images, layered files (i.e. files that have been adjusted in Photoshop or similar software), and RGB and CMYK colours.
• JPG or JPEG: Designed to make large photos smaller through compression, while still keeping a higher image quality. If images are compressed too much, however, this can still damage the image quality. Be sure to check with your publisher about the specific file sized they prefer. JPG files cannot store transparency in images but can be either RGB or CMYK colours.
• PSD: These files are almost exclusively created by and used in Photoshop. It can store transparency, different image layers, RGB and CMYK colours and is used by graphic designers and industry professionals. If you do not have Photoshop and are using a different software for your images or graphics, it’s best to save them as TIFF files.

4.2 Preferred image files for web/screen image publishing

• PNG: Can store transparency well and also allows image compression like a JPG. It can only hold RGB colour, however, so PNG files are only good for web or screen use. You should supply your publisher with TIFF files, rather than a PNG.
• JPG or JPEG: Designed to make large photos smaller through compression, while still keeping a higher image quality. If images are compressed too much, however, this can still damage the image quality. Be sure to check with your publisher about the specific file sized they prefer. JPG files cannot store transparency in images but can be either RGB or CMYK colours.
• GIF: Used on the web for graphics and short, basic animated images. You shouldn’t supply your images as GIF files. Instead, use a TIFF file.
• SVG: This file type can be zoomed in or out at any scale and not show any pixelisation. It’s great for web and screen images because of this, but it must be created in specialised software. A SVG can hold transparency, RGB and CMYK, and can also store layers.

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5. How to prepare and send your images for publishing

5.1 Do:

• Provide original files: It’s best to give a publishing company copies of your original files, not to screenshot or print them out to scan them. If you’re worried about the amount of files you need to send, you can always compress them in a ZIP folder, or send them through a free WeTransfer
• Source high-quality scans: If you only own a physical photo or copy of the image, you’ll need to get it scanned. Some home scanners do produce good scans, but it’s always best to go somewhere like Officeworks or similar to get your photos scanned at a high-quality. This will help to ensure that your image will print as best it can in your book.
• Provide images with transparent content as TIFF files: Some image files don’t keep transparency or can’t be CMYK even if they do. TIFF files, on the other hand, are compatible with various software, maintain an image’s transparency, and can be stored as CMYK, making them perfect for printing.

5.2 Don’t:

• Give your publisher screenshots or print-screen images: This reduces the quality of images substantially and opens you up to imperfections, like cursors or notification pop-ups, that will need to be removed. Any editing done to your images will likely cost you, so it’s best to steer-clear of these issues and just supply the original image files to your publisher.
• Supply photos of images: Like with supplying screenshots or print-screen images, supplying photos that you’ve taken of printed photos reduces the quality of images substantially. This is especially true if you leave the plastic sheets over photos in an album when you take the photo. It’s best to scan the photos into your computer and send them to your publisher. If you don’t have a scanner at home, it’s possible to go to a friend or a library and see if they can assist you. Stores such as Officeworks also offer scanning services and can help you get the best out of your images.
• Provide images with transparent content as a JPG or PNG: This was covered in section 4: Different file types, but it’s important to send files with transparency as a TIFF. This will save the designers in the publishing house time when working on your project and get your book out there quicker.
• Send images below ### if you intend them to be full colour and large: If you want your image to look effective and be high-quality, you have to supply an image with the file size of 200 KB or more. Your designer will advise you of the quality of your images and how you can use them during the design of your book.

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