68 LXF257 December 2019 http://www.linuxformat.comTUTORIALS HDR photography
In particular, depending on the exposure, either
lighter areas such as the sky could be an almost
uniform white, or the darker areas, for example
shadows, a uniform black. HDR – that’s High Dynamic
Range photography – overcomes this problem, as
we’re about to see.Say cheese!
The basic principle of HDR photography is to take
several photos at different exposures, so that between
them, you’ve captured much more of the tonal variation
that was present in the scene than can be recorded in a
single shot. Later on we’ll investigate ways in which
those multiple shots can be combined to create a single
HDR photo, but to start we need to give some guidance
on taking a set of photos at different exposures, or a set
of bracketed shots as photographers would say.
Since they’ll eventually have to be combined, it’s
important that all the differently exposed shots are
framed identically. In fact, if there’s a slight error you’d
be able to correct it by cropping your set of photos soccording to a large majority of digital camera
users, the quality of photos depends on one
thing and one thing only: resolution, in
megapixels. If only things were that simple. In reality
there are loads of facts and figures that differentiate
a good camera from a mediocre one, but we’d like to
think specifically about just one here: the dynamic
range. In plain English, this is a measure of the
difference between the dimmest and the brightest
element in an image that can be recorded.
You could find a range of up to 100,000:1 in some
daylight scenes, while the human eye can cope with
many thousands to one. The depressing fact is that
cameras don’t come close to the eye, even though a
good DSLR will perform better, in this respect, than
most phones or point-and-click cameras. The upshot
is that it’s often impossible to correctly record the
subtleties of tone in both the brightest and darkest
areas of many scenes. The limited dynamic range of a
camera can result in a serious lack of detail compared
to what you saw with your eyes.GIMP enables
two images to
be combined by
handling them
as layers, the
top one being
rendered partially
transparent using
a mask, so parts of
the bottom image
show through.Creating HDR photos
with open source tools
Mike Bedford investigates how to generate dramatic photos,
containing much more of the tonal variation we actually see in a scene.
Mike Bedford
finds there’s
something rather
special about
processing the
results of his
photographic
labours.A
GIMP
OUR
EXPERTYour camera or
phone might
have a built-in
HDR mode,
which does
much what
we’ve seen
here but behind
the scenes.
For the best
results, though,
there’s no real
alternative to
investing some
time and effort.Credit: http://www.gimp.org68 LXF257 December 2019 http://www.linuxformat.com
TUTORIALS HDR photography
Inparticular,dependingontheexposure,either
lighterareassuchastheskycouldbeanalmost
uniformwhite,orthedarkerareas,forexample
shadows,a uniformblack.HDR– that’sHighDynamic
Rangephotography– overcomesthisproblem,as
we’reabouttosee.Saycheese!
ThebasicprincipleofHDRphotographyistotake
severalphotosatdifferentexposures,sothatbetween
them,you’vecapturedmuchmoreofthetonalvariation
thatwaspresentinthescenethancanberecordedina
singleshot.Lateronwe’llinvestigatewaysinwhich
thosemultipleshotscanbecombinedtocreatea single
HDRphoto,buttostartweneedtogivesomeguidance
ontakinga setofphotosatdifferentexposures,ora set
ofbracketedshotsasphotographerswouldsay.
Sincethey’lleventuallyhavetobecombined,it’s
important that all the differently exposed shots are
framed identically. In fact, if there’s a slight error you’d
be able to correct it by cropping your set of photos soccordingtoa largemajorityofdigitalcamera
users,thequalityofphotosdependsonone
thingandonethingonly:resolution,in
megapixels.If onlythingswerethatsimple.Inreality
thereareloadsoffactsandfiguresthatdifferentiate
a goodcamerafroma mediocreone,butwe’dliketo
thinkspecificallyaboutjustonehere:thedynamic
range.InplainEnglish,thisisa measureofthe
differencebetweenthedimmestandthebrightest
elementinanimagethatcanberecorded.
Youcouldfinda rangeofupto100,000:1insome
daylightscenes,whilethehumaneyecancopewith
manythousandstoone.Thedepressingfactisthat
camerasdon’tcomeclosetotheeye,eventhougha
goodDSLRwillperformbetter,inthisrespect,than
mostphonesorpoint-and-clickcameras.Theupshot
isthatit’softenimpossibletocorrectlyrecordthe
subtletiesoftoneinboththebrightestanddarkest
areas of many scenes. The limited dynamic range of a
camera can result in a serious lack of detail compared
to what you saw with your eyes.GIMP enables
two images to
be combined by
handling them
as layers, the
top one being
rendered partially
transparent using
a mask, so parts of
the bottom image
show through.Creating HDR photos
with open source tools
Mike Bedfordinvestigates how to generate dramatic photos,
containingmuch more of the tonal variation we actually see in a scene.
MikeBedford
finds there’s
something rather
special about
processing the
results of his
photographic
labours.
A
GIMP
OUR
EXPERTYourcameraor
phonemight
havea built-in
HDRmode,
whichdoes
muchwhat
we’veseen
herebutbehind
thescenes.
Forthebest
results,though,
there’snoreal
alternativeto
investingsome
timeandeffort.Credit: http://www.gimp.org