A photo can look sharp on a phone and still look soft when it fills a book page. To estimate print detail, check the image’s pixel dimensions against the size it will occupy after cropping. The useful number is its effective pixels per inch (PPI) at that placed size—not simply the resolution number written in the file metadata.
Adobe explains that pixel dimensions describe how much image data exists, while print resolution describes how densely those pixels are placed on paper. Changing a resolution field without resampling does not create new image detail. This guide gives you a quick way to assess each image before you lay out a photo book.
Calculate the effective PPI in four steps
- Find the real pixel dimensions. Open the original photo in an image editor or file-properties tool. Record width and height in pixels; do not use a social-media preview or a screenshot of the original.
- Account for the crop. If the layout cuts off part of the image, use the dimensions of the cropped area, not the untouched original. A tight crop spends pixels.
- Measure its final placed size. Note the image width and height in inches (or convert centimetres to inches by dividing by 2.54) in the layout. For a full spread, calculate each direction using the whole printed span you intend the image to cover.
- Divide pixels by inches. Effective PPI = cropped pixel width ÷ placed width in inches. Check height the same way. The smaller result is the limiting direction.
Example: suppose a cropped photo is 2400 × 1800 pixels and you place it 8 × 6 inches. That is 300 pixels per inch in each direction. If you enlarge the same crop to 12 × 9 inches, it becomes 200 PPI. The file has not lost pixels; those pixels are simply spread across a larger area.
Why “300 DPI” is not a complete answer
People often say “DPI” when they mean image PPI. Printer dots per inch describe the output device; pixels per inch describe image sampling at the size used in your page layout. A common 300-PPI target can be a useful planning reference for many book images, but it is not a universal pass/fail threshold. Image detail, paper, output process, viewing distance, sharpness and the printer’s own requirements all matter. Follow the specifications for your actual job if they are available.
Also, the PPI value shown in an image file can be misleading if you ignore pixel dimensions and physical size. Adobe notes that changing resolution without resampling changes the potential printed dimensions, not the number of pixels. Upsampling can enlarge a file’s pixel grid, but it cannot recover genuine detail that was never captured.
Check spreads and edge-to-edge images carefully
For a photo crossing two facing pages, estimate PPI using the entire placed width, then inspect the center fold separately. Faces, captions and other important details should not land in the gutter. If the picture reaches the outer page edge, the file may need bleed, but the exact bleed amount depends on the printer’s template. Amazon KDP’s guide, for example, describes its own 0.125-inch bleed rules; use your actual production specification rather than copying one provider’s measurements into every project.
What to do when an image is below your target
- Reduce its placed size. A smaller print uses the available pixels more densely.
- Choose a looser crop. Restoring more of the original image can recover effective resolution.
- Use it as a small inset or thumbnail. A lower-resolution photo can still work at a modest size.
- Find the original export. Ask the photographer for the full-resolution source rather than enlarging a messaging-app copy.
- Print a page test. Inspect a full-size sample or proof at normal reading distance; a zoomed screen view is not the same as ink on paper.
Do not “fix” every warning by clicking an upscale button. Keep the untouched original, resize a working copy only when needed, and compare the result at final size. If the photo carries important evidence or fine detail—such as text on a document—consider whether a sharper source is essential before committing to the layout.
Make an image audit sheet before export
| Page | Image/source | Crop pixel size | Placed size | Effective PPI | Action |
|---|---|---|---|---|---|
| Example 8 | Original camera file | 2400 × 1800 | 8 × 6 in | 300 × 300 | Keep; inspect proof |
| Your page | Record file name | Use cropped dimensions | Use final layout size | Calculate both axes | Keep, reduce, recrop or replace |
Run this check after the layout is stable. Moving or enlarging an image changes its effective PPI; replacing it with a cropped or compressed copy can change the result too. Then export the final PDF and inspect the actual pages—not just the original image folder.
Preparing a one-copy photo book
Your Book Bound’s $99 USD service includes one hardcover, manual file checking, layout and cover support, digital proof revisions and standard tracked global delivery. If you are unsure about a few images, mark their page numbers and send the final interior PDF for review. Submit your book files for a manual check.