dialogue box. The most important thing you’ll see is a line
graph, with the levels graph shown faintly in grey as a
background. The line graph shows how the brightness levels
currently in the image (i.e. the input), which are represented
on the horizontal axis, will be transformed into the brightness
levels after selecting OK, (i.e. the output), which are
represented on the vertical axis. The initial line sees the input
and output have the same value, which means that even if you
click on OK, nothing will change.
The sky’s the limit here, and you could make some major
alterations to your photo or even create some surreal effects,
as you’ll discover if you start to play around by dragging
points on the curve to change its shape from its initial straight
line. However, we’d like to recommend a particular way of
editing the curve that will make a beneficial change to most
photos. This involves changing the straight line into what is
often referred to as anS-shapedcurve,althoughinrealityit
only slightly resemblesa letterS.Asyoucanseeinthe
screenshot, the way inwhichtheshapeofthecurvedeviates
from a straight line isinhavingslightcurvedsegmentsatthe
left-hand and right-handedgesofthelinetoreducethe
steepness of the lineintheseareas.Theresultofthisisto
enhance the contrastbymakingsomeofthedarkerareasin
shot even darker andmakingsomethelighterareaseven
lighter, while keepingthemidtoneslargelythesame.Again,
the effect can be quitedramatic.
Note that, by default,thiscurvewillapplytoallcolours,
although it’s possible,byselectingRed,GreenorBlueagainstManyofthetechniqueswe’vealreadyseenformaking
good photos evenbettercanbeusedtocorrect
photographic faults,althoughin thatcaseyou’llonlybe
making a poor photomediocre.So,forexample,adjusting
levels can improvetheappearanceofunderor
overexposed shots,althoughit can’tprovidedetailthat
has been lost in over-exposedhighlightsorunderexposed
dark areas. Similarly,youcancorrecta photowitha
horizon that’s far fromhorizontalorthathasbeenvery
badly framed usingthemethodsalreadydescribed.Bear
in mind, though, thatseverelycroppinga photowill
reduce the pixel countandwilllimitthesizeit canbe
displayed or printedin.
A commonly requiredformofcorrectionis tosharpen
a photo that looksblurred,eitherduetocamerashake,
poor focus, or mistonthelens.Althoughyoumightbe
able to achieve a degreeofimprovement,though,we
need to be honestin pointingoutthatthesharpening
function – which wesawin thediscussiononeditingfor
printing – isn’t reallygoingtocorrectthesefaults.The
problem is that anythingthatcausesa phototolook
blurred will have causedinformationtobelost.Theend
UHVXOWRIVKDUSHQLQJPLJKW ORRN VKDUSHUVXSHUÀFLDOO\EXW
in reality it’s not abletorestorethedetailthatwaslost.CORRECTING FAULTS
Many photo editors allow you to enhance contrast, but GIMP’s curve
feature offers much more flexibility.
Rather thanusingGIMP’sdodgeandburntool,werecommend
a much moreeffectivemethod,employinglayers.March 2020 | |^45
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Photo editing in GIMP