What is Optical DPI in Manga Digitization?
DPI (Dots Per Inch) describes the physical sampling frequency of a scanner sensor. In manga scanning, knowing your DPI is vital: if a scan is sampled below 600 DPI, physical printed screentone dots cannot be mathematically resolved, resulting in destructive moiré wave artifacts.
This tool calculates the exact DPI used to produce a given digital image file, helping you verify whether a scanned page meets professional archival preservation standards.
Mathematical Formulas & Methodology
// 1. Convert Physical Dimensions to Inches:
Physical Width in Inches = Physical Width (mm) / 25.4
Physical Height in Inches = Physical Height (mm) / 25.4
// 2. Compute Individual Axis DPI:
Horizontal DPI = round( Digital Pixel Width / Physical Width in Inches )
Vertical DPI = round( Digital Pixel Height / Physical Height in Inches )
// 3. Average DPI Calculation:
Average DPI = round( ( Horizontal DPI + Vertical DPI ) / 2 )Optical Density Rating Standards
| Calculated DPI | Tier Classification | Suitability for Manga Halftones |
|---|---|---|
| 600+ DPI | Archival Master | Moiré-free. Halftone screentone dots resolved cleanly as discrete shapes. |
| 300 – 599 DPI | Standard Print | Acceptable for clean continuous-tone color covers; moderate risk of screentone moiré on B&W pages. |
| 150 – 299 DPI | Web / Mobile | Suitable only for mobile reading; text is legible but fine screentones will show dot clamping. |
| < 150 DPI | Sub-optimal | Severe pixelation. Furigana readings and fine crosshatching will blur into illegibility. |
Beware of Non-Square Pixels
If your Horizontal DPI and Vertical DPI diverge by more than 2%, your image has suffered non-uniform stretching or was scanned on a hardware device with an uncalibrated stepper motor. Manga linework requires perfectly square 1:1 pixel sampling.