Formula
The usual press factor is twice the lines per inch:
pixels = inches × lines per inch × quality factor
The PPI page multiplies inches by a pixel density you type directly. This page builds that density from a line screen. One slug covers the photo and printing names.
Assumptions
- The quality factor is how many pixels you want per line of the screen.
- Both edges use the same line screen.
- The inches are the image, not the paper plus bleed.
Worked example
An 8 by 10 inch image at 150 lines per inch and a factor of 2 needs 2,400 × 3,000 px.
Input definitions
- Line screen
- Lines per inch in the halftone.
- Quality factor
- Pixels per line. Two is the common planning factor.
Limitations
This is a planning figure from the numbers you type. It is not a measurement of a network, a camera, a printer, or a power supply.
Questions
Why multiply by two?
A factor of two samples the line screen twice. Type another factor if the shop asks for it.
How is this different from 300 PPI?
150 lines times 2 is 300, so the example matches 300 PPI. The inputs are the screen and the factor, not a single density.