I have a lot of images in 300 dpi that I'm gonna use in the print version of a book. I want these same images in 72 dpi to be used in the digital version. How can I reduce the DPI without changing the display size? I use Photoshop and I notice when I change DPI, pixel dimension is reduced but document size keeps the same. I don't know if it's right.
What you need is to resample a copy of them.
If you are using Photoshop:
- Image size
- Change the units for a phisical unit (cm or inches)
- Check the resample checkbox
- Change your ppi. This will make a smaller size image, but will be translated into your print as a lower resolution image of the same phisical size.
If your book is already designed, what is best is to export a pdf and let the pdf export resample them for you.