Ask Uncle
Ronnie
Exposing for HDR
I have tried my hand at creating
HDRs but have always failed. While
I seem not to have any issues while
post-processing in Photoshop,
I think my problem is knowing
exactly how to expose for HDR. Can
you help?
Arun Pathak, via emailFor those who may not be aware,
the imaging sensor in our digital
cameras cannot faithfully reproduce
the brightness range that is often
present in a brightly lit scene. HDR
imaging is a method that allows us to
record a higher range of brightness
than what is possible through a single
frame exposure. Generally, we create a
bracket of 3 or 5 frames with varying
exposures and then blend them
together using a suitable software.Many books have been written on
this topic which can get rather very
technical. I shall try to explain this in
a simpler manner.Mount your camera on a sturdy
tripod and compose your frame. For
best results, shoot in Raw but if your
computer is short on memory, you
may try shooting in JPEG.- ���������������������������������
capturing the highlights correctly,
but without clipping (overexposing)
the highlights. So expose a frame and
check the histogram. Since you are
exposing for the highlights, the picture
will be very dark and the histogram
will be very much to the left. You
���������������������������������������
to the right that the histogram has
not occupied. If so, take the next shot
with some more exposure so that the
histogram appears like what you see
Ask your question to Uncle at [email protected]
capturing as much shadow detail as
is possible. Remember, in step 1, we
have already captured the maximum
highlight detail, without overexposing
the highlights.Once the images are placed in the
HDR software, the software will merge
them by taking the properly exposed
���������������������������������������
properly exposed mid-tones from the
second exposure and the properly
exposed shadows from the third/last
������������������������������������
a range of brightness that would not
have been possible to capture through
a single exposure.Please caution on the side of ‘over-
cooking’ the image. HDRs often show
excessive shadow detail, which may
appear wrong to some people. After
creating an HDR image (and I love
HDR images), I often tone down the
shadow areas a wee bit so that the
image does not look over-processed.Filters and Image
DegradementI am new to photography. Some of
������������������������������������
���������������������������������
image quality.
���������������������������������- Can I use a welder’s glass in place
���������������������������������
Rajaram Bhat, via email - This is an ongoing debate – one
which will never end. To put it simply,
�������������������������������������
spotless, will not noticibly degrade
the image quality; even if it does in
theory, you are not likely to notice the
difference. However, a poor quality
in the accompanying sketch.Ensure that the highlights are not
clipped (overexposed).- For the second shot, ‘open up’ the
exposure by 2-stops but ensure that
this is done only by reducing the
shutter speed (the aperture should
remain the same during all the frames
that you shoot to create the HDR).
This should get us the proper mid-
tones. - Continue by taking the third shot
with another 2-stop extra exposure.
Keep an eye on the resulting
histogram. We want the begining of
the histogram (the shadow areas)
to go about halfway to the right as
possible. If that is not so, take one
more shot with a 2-stop increase
in the exposure, till the histogram
appears like what you see here.
The highlights are overexposed here
but we are concerned only with86 http://www.smartphotography.in
Smart PhotographyJuly 2017