MacFormat UK – June 2019

APPLE SKILLS How it works

54 | MACFORMAT | JUNE 2019 macformat.com @macformat

Preparing photos for printing

It’s not the dark art it once was, but take our tips for better output

YOU WILL LEARN

How to tweak photos

to look their best,

calculate resolution

and understand

colour printing

Whether you’re printing photos

on your inkjet, sending them

to a photo printing service or

including them in a printed

poster or brochure, a few quick checks

will help them look their best.

Colour is handled well by default these

days, from taking a picture with automatic

white balance to sharing image files with

embedded ICC colour profiles. The best way

to keep everything right is usually to leave

it as it is. If you have a non-Apple display,

its profile should be installed in ~/Library/

ColorSync/Profiles and selected in  > System

Preferences > Displays > Color.

If a pic looks washed-out, lacking contrast,

try the one-click fix options in photo-editing

software. In Photoshop, apply Auto Tone

(ß+ç+L); in Affinity Photo, Filters > Colours

> Auto Levels. Haze removal may also help:

find this in Affinity Photo in the Filters menu,

and in Photoshop as a slider in Camera Raw,

which opens when you import a raw photo,

or can be accessed by pressing ß+ç+A.

In Lightroom, similar options are in Develop

or Quick Develop.

Only manual shooters are likely to find pics

under- or overexposed, but to retrieve detail

lost in shadow, increase the Shadows slider;

to rescue blown highlights (where detail is

lost), decrease Highlights. This is most

effective during Camera Raw import, or

developing raw images in Lightroom, but can

be accessed from the Filters menu in Affinity

Photo or Image > Adjustments in Photoshop.

Up the resolution

When it comes to resolution, everyone knows

images for printing need to be 300dpi, right?

Well... It’s really 300 pixels, not dots, per inch.

(Don’t worry, everyone says 300dpi. And don’t

even think about converting it to metric.) The

number comes from halftone printing, where

images were traditionally rephotographed

through a screen to break up continuous

tone into discs of three primary colours –

cyan, magenta and yellow – plus black.

For magazine-quality printing, the halftone

screen would have 150 to 175 lines per inch.

Today a computer-to-plate system at the

press generates the halftone patterns, but the

principle is the same. So you’d probably guess

images would need 150-175 pixels per inch. In

fact, we need 1.5 to 2x the resolution to allow

for any misalignment between the images

and the halftone screen – hence 300ppi.

Laser printers (and toner-based digital

presses) do their own halftoning, but inkjets

work differently. Instead of regularly spaced

discs that bloat from points into squares the

more ink is required, they print tiny dots

of a fixed size scattered at random.

This frequency modulated (FM) rather than

amplitude modulated (AM) method is known

as ‘stochastic’ screening, from the Greek

for guessing. That’s why inkjet printers

work at ridiculously high resolutions, like

5760x1440dpi. Within each pixel, they print

lots of dots to create the right colour. The

image itself just needs enough pixels so that

the picture looks clear and detailed, not

fuzzy or blocky. It turns out that, for normal

eyesight at handheld viewing distance, about

240 pixels per inch is enough. Obviously,

though, you could still aim for 300ppi.

Key fact

Avoid the Calibrate

option in System Prefs

> Displays > Color, which

will probably make

things worse. If you’re

concerned about

display accuracy,

consider a hardware

calibrator such as

Datacolor’s Spyder5

(around £85) or the

new SpyderX.

Ever yone

knows images

for printing

need to be

300dpi, right?

Well...

HOW IT WORKS

Modern colour reproduction should give decent results by

default, but ensure the image resolution is high enough.