The most common way of turning a photograph into
a Web image file is to scan a print with an ordinary
flatbed scanner. Scanners have come down in price
quite significantly in the last year or so and even
the cheapest ones can give a reasonable, if not
great, image quality. Prints suffer from a number of
problems. Send the same negative to two different
labs and you will get quite different prints, or
even to the same lab on separate days. Commercial
prints are put through a kind of sausage machine,
they are never good at the best of times. All you
can expect is that they are 'acceptable' for their
purpose. Scanning such prints with a low-cost
scanner is also going to push the boundaries of
acceptability. Not only do you have the low contrast
and paper surface texture to contend with, the
scanner itself is probably not calibrated properly
and you are introducing yet another layer of errors.
If your scanner has adjustment facilities in its
scanning software, it is always better to make
serious colour and contrast corrections before
scanning and leave the image editor to do
fine-tuning. Correct any serious colour cast first
before adjusting the contrast otherwise you will
just make the wrong colours stronger.
The idea is to capture the maximum possible amount
of information in the picture file because the
process of image editing inevitably throws
information away, and you can't bring it back.
After scanning the print at about twice the required
final size, fine adjust the colour balance and tonal
levels. Most pictures have areas of black and white
in them, though not always. As a general rule, you
should use the 'levels' control to set the darkest
point of the picture to black and the lightest point
to white. You can do this with the sliders or with
the dark and light eyedropper tools.
The tonal graph should, ideally, span the total
width of the 'levels' window but here it is falling
short at both the high and low ends (left and right).
Moving the pointers inwards (red) to match the
darkest and lightest parts of the image (the pale
yellow area) increases its contrast just like
turning up the bass and treble on a hi-fi system.
The middle arrow can be moved towards the left (green)
to 'open up' mid-tones that are too dark.
Unfortunately, this process does not introduce new
information, you don't get anything for nothing, it
just stretches what's there is to fit. For best
results, the scanner should be adjusted to make sure
it captures the full tonal range from the outset.
You will have to check your scanner software manual
for instructions how to do that.
When the image looks right, and you have removed any
blemishes, reduce it down to its final size. If you
reduce the image any more than about 50%, you might
need to apply a small degree of sharpening, or 'unsharp
masking', which is more controllable and not so
severe. Over-sharpened images look just as bad, or
even worse, than soft ones. If your subject is a
face, for instance, try just sharpening the eyes. It
is amazing how a crisp highlight in the eyes can
seem to bring a blurred portrait into focus.
Note: If the full version of Adobe Photoshop is too
expensive for you, Adobe Photoshop Elements gives
you most of the facilities of the full version for a
fraction of the price and I highly recommend it.
Some of the problems associated with scanned prints
can be sidestepped by scanning transparencies or
even negatives. Some flatbed scanners have
transparency adapters but these are usually
hopelessly inadequate for small film formats like
35mm or APS, even for the relatively low demands of
a Web page image.
Dedicated film scanners give the best possible file
quality, and this is what professionals use. A
transparency (or even a negative) contains a greater
amount of detail and contrast. Where prints are
always viewed by reflected light, and much of the
available light is lost by scattering and absorption,
the light passing through a piece of film remains
relatively unscathed. The contrast ratio, the
difference between the lightest and darkest parts of
the image, is always much better in transmitted
light.
Professional film scanners used for print work are
extremely expensive but there are 'desktop' models
that are more affordable and produce superior image
quality to their flatbed counterparts.
The only thing to watch out for with film scanners
is dust and dirt. The smallest hair will magnify to
horrendous proportions and it's considerably easier
to remove it with a puffer brush before scanning
than to have to do it in Photoshop afterwards.
Don't be tempted to scan at too high a resolution
with any kind of scanner. Reducing the image always
has a softening effect. If you do have to reduce an
image by a significant amount, do it in stages – 50%
at a time – applying a small amount of unsharp
masking at each step rather than trying to do it all
at once at the end.
Like scanners, digital cameras are becoming more
affordable although they still cost more than much
more capable 35mm cameras. For Web pictures, just
about any digital camera will do. You don't need
very high resolution but the more expensive high
resolution cameras do tend to be better in other
areas too – colour accuracy, zoom lenses, macro
facilities etc. Get the best one you can afford but
don't plan on keeping it too long because you will
probably want a new one in a year's time, one that
is even better and probably only half the price.
When you have the image you want on your screen, the
final process is to reduce the file size for
transmission over the internet without compromising
its quality. This invariably means saving it in JPEG
format (.jpg). JPEG is a 'lossy' format that allows
you to trade-off file size against image quality.
Compress the image too much and it will have all
kinds of nasty blemishes. You can only do this
visually, there is no magic formula.
I like to reduce the compression setting to the
point where the compression artefacts just start to
appear and then back-off a little. This 'threshold'
point varies considerably with the type of image
from about 35% to 65%. Busy images with lots of
texture can withstand higher compression than ones
with areas of flat colour and well defined edges.
In the end, photographic quality is subjective. If
you have a picture of a flying saucer hovering over
the Whitehouse, the quality should be poor to be
believable - and hide the wires. At most other times,
it should be as good as you can possibly get it.
