Colour printing APPLE SKILLS
macformat.com @macformat JUNE 2019 | MACFORMAT | 55Dedicated photo printing services often
use another technology: dye sublimation.
Here, the colour ingredients are heated and
diffused into the paper, with no halftoning or
stochastic screening; in effect, every pixel is
printed directly in its own colour. For this
method, images should be supplied at the
printer’s native resolution, usually 300dpi.
There’s no such thing as a ‘300dpi photo’,
because an image file doesn’t have a physicalsize. If it’s, say, 1800x1200 pixels, then if you
print it at 6x4 inches it’ll be 300dpi, but at
12x8 inches it’ll be 150dpi. To check the
effective resolution of an image file, open it
in your photo-editing software and go to the
Image Size dialog (ç+å+I in Photoshop or
Affinity Photo). Turn off Resample: now any
changes won’t affect the image itself, so the
number of pixels will stay the same. Then
change the units from pixels to inches or
centimetres, and enter a value to see the
resolution; or change the resolution to 240
or 300ppi and see what size you get.
If the resolution is too low, turn on
Resample and increase the size, using Bicubic
interpolation (or try any other option except
Nearest Neighbour), and judge the result for
yourself, at 100% zoom. You’re not adding any
detail, but up to 120% or so, it may still look
fairly sharp. If the resolution is too high, on the
other hand, don’t bother reducing it except to
make a smaller file (perhaps to meet an upload
limit) or to use Photoshop’s Bicubic Sharper
mode to increase the impression of detail in
a pic you’re going to print very small. Save
the edited file separately. Adam BanksKey fact
Even if preparing
photos for a CMYK
output process, never
convert them to CMYK
yourself, or edit them in
CMYK mode, unless your
printing service requires
it. It’s more reliable to
keep everything in RGB,
ideally in a large working
space such as Adobe
RGB (1998) – check
your app’s colour
management settings –
until the printer’s
system converts
them for output.2
Shadow
Increasing the Shadows slider pulls
detail out of dark areas. You may need
to add some saturation back (Photoshop
does this automatically). If the detail isn’t
important, though, leave shadows dark
(‘crushed’) for a stronger look.3
Highlight
The Highlights slider can work wonders
on washed-out pale grey British skies,
as long as your camera captured some
detail. This works best on Raw files.
You may need to increase contrast
and saturation a little too.1
Unsharp
Lack of sharpness, from poor focus
or slight camera shake, can rob a pic of
pop. Try an Unsharp Mask at 70-150%
with Threshold at 4, increasing the
Radius from one pixel up to about 4
depending on resolution and softness.EXPLAINED... Quick photo fixes
If you must print JPEGs, save at max quality, but for zero
degradation, use your app’s native format or TIFF (with
LZW compression if asked). Retain originals as a fallback.