~ by Brad Schmidt, Technical Support Specialist
When you’re preparing a book for print, image resolution might seem like a small detail, but it plays a big role in how your final product looks and feels. Ensuring your images are crisp and clear is key to delivering a professional result.
What Is Image Resolution?
Image resolution refers to the amount of detail an image holds, measured in pixels per inch (ppi). For print, the recommended resolution is 300 ppi for both colour and greyscale images. Anything lower…especially below 200 ppi…can result in blurry or pixelated images that detract from the quality of your book.
Actual vs. Effective Resolution
There are two types of resolution to keep in mind:
- Actual resolution is the resolution of the image as it exists in Photoshop before it’s placed into your layout.
- Effective resolution is what happens after you resize the image in your layout software, such as InDesign.
For example, if you shrink an image in InDesign, its effective resolution increases. If you enlarge it, the effective resolution drops. This resizing often happens during the design process, which makes effective resolution a bit trickier to track.
Why it Matters for Printing
At Friesens, checking image resolution is a key part of our preflight process…the final check before your files go to press. Images with low effective resolution are flagged because they can compromise print quality. We want your book to look its best, and that means making sure every image is sharp and print ready.
How to Check Resolution in InDesign
InDesign makes it easy to check both actual and effective resolution:
- Use the Preflight tool to scan your entire document. It will flag any images that fall below the recommended resolution.
- If you want to check a single image, the Info palette is a handy shortcut. Just make sure to enable “Show/Hide Link Information” to see all the details.
Bonus Tip: Watch Your Colour Profiles
While you’re checking resolution, it’s also a good idea to look at your colour profiles. InDesign’s Info palette shows the working space profile of the document, not the embedded profile of the image. To make sure your document and images are aligned, go to Edit > Assign Profiles and set the CMYK profile to match your press settings.
Common Mistakes to Avoid
Even experienced designers can run into resolution issues. Here are a few common pitfalls to watch out for:
- Using web images for print: Images downloaded from websites are often 72 ppi…great for screens, but not suitable for print. Always check the resolution before placing them in your layout.
- Enlarging small images: Upscaling a low-resolution image in InDesign might make it fit the layout, but it reduces the effective resolution and can lead to poor print quality.
- Ignoring effective resolution: Designers sometimes focus only on actual resolution, forgetting that resizing in the layout affects the final output. Always check both.
- Skipping the preflight check: InDesign’s Preflight tool is there for a reason. Use it to catch resolution issues before they become printing problems.
- Mismatched colour profiles: If your document and images use different profiles, colours may shift unexpectedly during printing. Assign a consistent profile to avoid surprises.
Image resolution might seem like a technical detail, but it’s one of the most important steps in preparing your files for print. Taking the time to check and adjust resolution ensures your images are sharp, your colours are accurate, and your readers are impressed.
