AV News 178 - November 2009
Photoshop - Image Registration
Keith Scott FRPS
One obvious reason for registering several images is to take advantage of
HDR (higher dynamic range) incorporating different exposures into a single
image, thereby producing maximum detail throughout shadow and highlight
areas. This is a subject that we've touched upon before. However in this
instance the need to register several images is entirely different. One of my
colleagues had taken several photographs of church candles. He needed to
register and trim each image so that he could use them sequentially within his
latest AV presentation, presumably to enable the candle bodies to remain
stationery while showing movement of the flickering flames.
Original exposures were all taken with the camera mounted on a sturdy
tripod which actually helps Photoshop to interpret the required registration. Not
just because these images would be quite close to register anyway, but
because the images should be free from camera shake and therefore sharper.
Higher levels of sharpness (not just post exposure software sharpening) helps
Photoshop identify similar pixel edge tones and contrasts, thereby aiding the
alignment process. Remember Photoshop cannot think and it doesn't know or
care what your image content is, it just compares the properties of pixels.
Of course not all versions of Photoshop include these alignment functions we
are about to explore and I know that many readers are still using versions 5, 6
or 7. Unless they have a very good reason to spend money on updates, I
suggest they live with the version they have until it outlives its usefulness.
However if you already have version CS3 or CS4 then you certainly have this
useful set of tools available. This procedure is quite simple and in theory
consists of the following: open several different images onto separate layers
within a Photoshop file. Lock one layer to prevent it moving, and then align all
other images to the locked layer. After alignment crop to whatever size you
need, then save each layer as a .jpg file for use in your sequence.
So that's the
theory but how
do we actually
do it. Under the
main File menu
click on Scripts
then on Load
Files into Stack,
at this point a
control box will
appear, which
will enable the
selection of the
files
to
be
opened.
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