http://www.techradar.com/pro/linux December 2019 LXF257 69HDR photography TUTORIALS
By using GIMP to combine a photo with the foreground exposed correctly and one with a properly
exposed sky, the resultant image includes a dramatic sunset and a fully visible foreground.SINGLE-IMAGE HDR
they all show exactly the same scene, and some HDR
software can do that automatically – but it’s better if
you get it right from the outset. The only surefire way of
doing that is to use a tripod, and if you don’t have one,
you’ll be pleased to hear that they can cost just £10 or
even less for very compact ones.
Ideally, we’d also recommend using a remote control
or cable release, so that you don’t risk moving the
camera on its tripod when you press the shutter release- but the benefit is somewhat reduced because you’re
going to have to touch your camera between shots, to
adjust the exposure. Actually, bracketed sets of photos
can sometimes be taken automatically with a single
press of the shutter release button, but this isn’t
available on all cameras – and even when available, it
might not give you enough control for HDR work.
The process involves fixing your camera on a tripod,
framing the scene, taking a photo at one exposure,
altering the exposure setting using your camera’s
exposure compensation feature, taking another photo,
and continuing until you’ve got all the exposures you
need. You’ll need one correctly exposed shot and, as a
very minimum, shots that are underexposed by one and
two stops (-1EV, -2EV) and overexposed by one and two
stops (+1EV, +2EV). For some scenes you’ll need to go
further than -2EV and +2EV, but you’ll learn from
experience, and it’s always better to get more shots
than you really need, than too few.
Try to work as quickly as possible to eliminate any
problems of clouds moving in the sky between shots –
which, depending on the method you use for combining
the shots, could cause problems. Don’t worry if you
notice, when you review your set of photos, that some
are almost all black while others are almost all white.
While such shots would be virtually useless as
standalone photos, they could still contain small areas
that are correctly exposed and, therefore, will make
useful contributions to the final HDR photo.
Also, by all means capture as many exposures as
you want, but bear in mind that, when you come to
process them, you may not be able to use them all.
In particular, shots over-exposed by more than about
3EV could well suffer from effects that will manifest
themselves either as haze in parts of the image or
even a prismatic rainbow appearance. The eagle-eyed
might just notice this effect in a couple of the images
presented here.
With a bit of time and effort it might be possible to
minimise these artefacts in post-processing, but it’s
easier to avoid it from the start. The effect is known as
lens flare and is a fairly common phenomenon when
shooting into the light. Overexposing a shot increases
the chances of it being visible. Using a lens hood is a
good way of reducing flare.
Finally, we need to provide some guidance on how
to underexpose and overexpose your shots. Generally
speaking, there are two methods. You can set the
camera to Aperture Priority mode and pick an aperture,
so that when you use your camera’s exposure
compensation feature it alters the shutter speed. Or
you can set the camera to Shutter Priority mode and
pick the shutter speed, so when you use your camera’s
exposure compensation feature it alters the aperture.
Both have their pros and cons for general use but, in
most cases, you’ll get better results for HDR work if you
use Aperture Priority. This is because the aperture
affects the depth of field, which is something you’ll want
to be the same between individual shots.The manual method
A common experience is to take a photo which ends up
having an almost featureless white or pale grey sky,
even though it was a pleasing blue colour with
contrasting white clouds to your eye. This happens
when the camera exposes the shot so that the
foreground is correct, with the result that the sky is
overexposed. To start our investigation of how to
process a set of photos to generate an HDR result, we’ll
take exactly this case as an example of how to increase
the dynamic range manually, using just a photo
manipulation package.
This isn’t the only scenario in which this method is
suitable, but it’s probably the most common. The effect
is different from that achievable with dedicated HDR
software that we’ll look at later, but the result often
appears more natural. We’re going to use GIMP (GNU
Image Manipulation Program), but you’ll be able to getCreating a proper HDR image requires several exposures but, if you
only have the one, you might be able to go some way to replicating
the effect. This is possible when some tonal differences are present in
areas that look ostensibly uniform. The most intuitive way of finding
out if this is the case in GIMP is to select Colors > Brightness-
Contrast and try adjusting the Brightness slider to the left. If the
result is that a uniform white sky simply becomes a uniform grey,
then there is no detail in the sky, so it’s game over. Conversely,
moving the Brightness slider to the right will reveal if there’s any
hidden detail in apparently uniform dark areas.
If you discover hidden detail in the light and dark areas, first reduce
the brightness until acceptable detail can be seen in the light areas
and save the result with a different filename, and then do the same
with the dark area. You now have two photographs of the scene, one
with detail in the dark areas and one with detail in the light. You can
now use these two images to generate an HDR image using GIMP.We said the
human eye
has a dynamic
range of a few
thousand to
one, but it can
actually be
larger. That
figure refers
to the range
that can be
perceived in a
single scene,
but it’s billions
to one if we
compare bright
daylight and
night-time
scenes.6668Decmbr rb8c2019b21invst December 2019 LXF257 69
HDR photography TUTORIALS
ByusingGIMPtocombinea photowiththeforegroundexposedcorrectlyandonewitha properly
exposedsky,theresultantimageincludesa dramaticsunsetanda fullyvisibleforeground.SINGLE-IMAGE HDR
they all show exactly the same scene, and some HDR
software can do that automatically – but it’s better if
you get it right from the outset. The only surefire way of
doing that is to use a tripod, and if you don’t have one,
you’ll be pleased to hear that they can cost just £10 or
even less for very compact ones.
Ideally, we’d also recommend using a remote control
or cable release, so that you don’t risk moving the
camera on its tripod when you press the shutter release
- but the benefit is somewhat reduced because you’re
going to have to touch your camera between shots, to
adjust the exposure. Actually, bracketed sets of photos
can sometimes be taken automatically with a single
press of the shutter release button, but this isn’t
available on all cameras – and even when available, it
might not give you enough control for HDR work.
The process involves fixing your camera on a tripod,
framing the scene, taking a photo at one exposure,
altering the exposure setting using your camera’s
exposure compensation feature, taking another photo,
and continuing until you’ve got all the exposures you
need. You’ll need one correctly exposed shot and, as a
very minimum, shots that are underexposed by one and
two stops (-1EV, -2EV) and overexposed by one and two
stops (+1EV, +2EV). For some scenes you’ll need to go
further than -2EV and +2EV, but you’ll learn from
experience, and it’s always better to get more shots
than you really need, than too few.
Try to work as quickly as possible to eliminate any
problems of clouds moving in the sky between shots –
which, depending on the method you use for combining
the shots, could cause problems. Don’t worry if you
notice, when you review your set of photos, that some
are almost all black while others are almost all white.
While such shots would be virtually useless as
standalone photos, they could still contain small areas
that are correctly exposed and, therefore, will make
useful contributions to the final HDR photo.
Also, by all means capture as many exposures as
you want, but bear in mind that, when you come to
process them, you may not be able to use them all.
In particular, shots over-exposed by more than about
3EV could well suffer from effects that will manifest
themselves either as haze in parts of the image or
even a prismatic rainbow appearance. The eagle-eyed
might just notice this effect in a couple of the images
presented here.
With a bit of time and effort it might be possible to
minimise these artefacts in post-processing, but it’s
easier to avoid it from the start. The effect is known as
lens flare and is a fairly common phenomenon when
shooting into the light. Overexposing a shot increases
the chances of it being visible. Using a lens hood is a
good way of reducing flare.
Finally, we need to provide some guidance on how
to underexpose and overexpose your shots. Generally
speaking, there are two methods. You can set the
camera to Aperture Priority mode and pick an aperture,
so that when you use your camera’s exposure
compensation feature it alters the shutter speed. Or
you can set the camera to Shutter Priority mode and
pick the shutter speed, so when you use your camera’s
exposure compensation feature it alters the aperture.
Both have their pros and cons for general use but, in
most cases, you’ll get better results for HDR work if you
use Aperture Priority. This is because the aperture
affects the depth of field, which is something you’ll want
to be the same between individual shots.The manual method
A common experience is to take a photo which ends up
having an almost featureless white or pale grey sky,
even though it was a pleasing blue colour with
contrasting white clouds to your eye. This happens
when the camera exposes the shot so that the
foreground is correct, with the result that the sky is
overexposed. To start our investigation of how to
process a set of photos to generate an HDR result, we’ll
take exactly this case as an example of how to increase
the dynamic range manually, using just a photo
manipulation package.
This isn’t the only scenario in which this method is
suitable, but it’s probably the most common. The effect
is different from that achievable with dedicated HDR
software that we’ll look at later, but the result often
appears more natural. We’re going to use GIMP (GNU
Image Manipulation Program), but you’ll be able to getCreating a proper HDR image requires several exposures but, if you
only have the one, you might be able to go some way to replicating
the effect. This is possible when some tonal differences are present in
areas that look ostensibly uniform. The most intuitive way of finding
out if this is the case in GIMP is to select Colors > Brightness-
Contrast and try adjusting the Brightness slider to the left. If the
result is that a uniform white sky simply becomes a uniform grey,
then there is no detail in the sky, so it’s game over. Conversely,
moving the Brightness slider to the right will reveal if there’s any
hidden detail in apparently uniform dark areas.
If you discover hidden detail in the light and dark areas, first reduce
the brightness until acceptable detail can be seen in the light areas
and save the result with a different filename, and then do the same
with the dark area. You now have two photographs of the scene, one
with detail in the dark areas and one with detail in the light. You can
now use these two images to generate an HDR image using GIMP.Wesaidthe
humaneye
hasa dynamic
rangeofa few
thousandto
one,butit can
actuallybe
larger.That
figurerefers
totherange
thatcanbe
perceivedina
singlescene,
butit’sbillions
tooneif we
comparebright
daylightand
night-time
scenes.