Resolution (DPI/PPI)

Image resolution and its relationship to print quality.

Core Concepts

DPI (Dots Per Inch)

The number of dots per inch in print. Determines the quality of physical output.

PPI (Pixels Per Inch)

The number of pixels per inch in a digital image. For print, effective PPI is calculated at the placed physical size; a metadata label alone is insufficient.

Note: In practice, DPI and PPI are used interchangeably. The term "DPI" is standard for print.

Resolution Guide

These are preparation examples; admission thresholds depend on the product, viewing distance, printing method and selected preflight profile. For screens, pixel dimensions and display scale matter more than a fixed 72 PPI label.

Usage	Example Lower Target	Recommended DPI
Web/Screen	72	72–96
Office print	150	200
Professional print	300	300–350
Large format (billboard)	72–150	100–150

Why 300 DPI?

            72 DPI              150 DPI             300 DPI
         ┌─────────┐         ┌─────────┐         ┌─────────┐
         │ █ █ █ █ │         │█ █ █ █ █│         │█████████│
         │ █ █ █ █ │         │█ █ █ █ █│         │█████████│
         │ █ █ █ █ │         │█ █ █ █ █│         │█████████│
         │ █ █ █ █ │         │█ █ █ █ █│         │█████████│
         └─────────┘         └─────────┘         └─────────┘
           Pixelated           Medium quality       Sharp

300 PPI is a common preparation target for photographic work viewed closely; it is not a universal cutoff for human vision. Lower effective PPI may suit large formats; confirm the producer's profile and actual viewing distance. A 72 PPI label alone does not make an image unsuitable for print: pixel count and placed size determine effective resolution.

Resolution Calculation

Formula

Pixels = Inches × DPI
or
Pixels = (mm ÷ 25.4) × DPI

Example: A4 Print

A4 size: 210 mm × 297 mm

Required pixels at 300 DPI:

Width:  (210 ÷ 25.4) × 300 = 2,480 pixels
Height: (297 ÷ 25.4) × 300 = 3,508 pixels

Common Sizes

Example Pixel Values (at 300 DPI)

Product	Size (mm)	Approximate Pixels
Business Card	85×55	1,004×650
A5 Flyer	148×210	1,748×2,480
A4	210×297	2,480×3,508
A3	297×420	3,508×4,961
A2 Poster	420×594	4,961×7,016

Checking Resolution

How to Check

Photoshop:

Image → Image Size → Resolution

Illustrator:

File → Document Setup → Raster Effects → Resolution

NowToPrint: Preflight evaluates measurable effective image PPI against the selected profile. For example, the sheetfed-offset rule marks below 250 PPI critical, while the universal profile warns below 150 PPI; GWG profiles have different thresholds. Unmeasured or unsampled coverage is not “sufficient.” Vector content is not evaluated through the same raster PPI threshold.

Can Resolution Be Increased?

Upscaling Limitations

Enlarging a low-resolution image with software does not add real detail:

Original 72 DPI → Software upscaled to 300 DPI = Blurry 300 DPI

Resampling Smooths Edges, Not Detail

Resampling only smooths edges; it cannot recover detail that was never captured. Even a smoothed result:

Is not as sharp as the original
Can lose detail
Is still risky for professional print

Recommended: Use the original high-resolution source file.

Large Format Print

Why Is Lower DPI Sufficient?

Large formats such as posters and billboards are viewed from a distance:

Distance	Example PPI
30 cm (business card)	300 DPI
1 metre	150 DPI
3 metres	72 DPI
5+ metres	50 PPI example

Summary

Check effective PPI at final size and the measurement coverage.
Confirm the product's print profile, colour/output-intent and bleed requirements.
Do not treat missing measurements or a threshold warning as automatic production approval.

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