A picture that looks sharp on a screen can print soft. Print needs more pixels for each inch than a screen does, and KDP sets a minimum for it.
What KDP asks
- 300 DPI at least. KDP recommends images of at least 300 DPI in the manuscript, sized at 100% and flattened to one layer. Cover images need 300 DPI as well.
- No enlarging after insertion. Insert an image at its original size. Enlarging it afterwards lowers its resolution.
- No set maximum. Very high resolutions can make a file time out in processing or delay printing. The largest file KDP takes is 650MB.
- Color only with color ink. A color photo prints in color only if you chose a color ink. A black-and-white photo prints in black and white with either ink.
How to work it out
DPI is the image's width in pixels divided by its printed width in inches. KDP's own example is an image of 1,200 × 1,800 pixels printed at 4 × 6 inches, which is 300 DPI.
| Printed width | Pixels across for 300 DPI |
|---|---|
| 2″ | 600 |
| 3″ | 900 |
| 4″ | 1,200 |
| 4.5″ | 1,350 |
| 5″ | 1,500 |
The same image has a different DPI at every size it is printed. Printed smaller, it gains DPI; printed larger, it loses it. So the number that counts is the one at the size in the finished book.
Changing the DPI figure stored in an image file adds no detail. Only more pixels do.
A picture that fills a page with bleed prints at the bleed size, not the trim size. On a 6 × 9 book that is 6.125 × 9.25 inches, so 300 DPI needs 1,838 × 2,775 pixels. KDP bleed or no bleed explains the page setup.
What to do with a low-resolution image
- Find the original. A photo sent by email or taken from a website has often been made smaller.
- Print it smaller. In Word, halving its width doubles the DPI.
- Leave it out, or replace it, if neither is possible.
What Torcul does
Torcul prints each picture at the width it has in the Word file, and never wider than the text. When you upload, it warns about any picture under 300 DPI at that width. A picture wider than the text prints narrower, so the last screen gives each picture's DPI as read from the finished PDF.
Sources
None of this guarantees that KDP will accept a file. KDP changes its help pages, so check the date on this one and on any report a tool gives you.