Correcting Horizons using Photoshop
by Chris Maddock
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Whilst one can use the Measure Tool to straighten horizons, a
quicker method that I prefer is using the Crop Tool. The advantage
to this is that it saves having to crop after rotating your image
and you can set it to retain the aspect ratio of the image - usually
I also use it to retain the overall image dimensions by having
it enlarge the cropped area slightly.
Firstly locate the Crop Tool. In PS7 it's third from
the top in the lefthand column of the toolbox. In its basic mode
it allows you to draw a rectangular selection over an image and
crop to that selection. However, as well as that it allows you
to rotate the selection and even resample the selection to a given
size.
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| Once the
Crop Tool is active, we need to set the options for it in the toolbar
as shown below. |
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I prefer
(unless the skew is very bad) to have the straightened image resized
to the original size so I have entered the Width, Height and Resolution
values of the original. If you leave them all blank the tool will
simply crop the image without resizing - it will also not be constrained
to an aspect ratio.
Having set the tool options, I now draw a selection over
most of the image, as below;
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| Now I drag
the selection so that one of the long edges is close to the horizon
that I want to straighten; |
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| This done,
I now move the cursor near to one of the selection corners and it
becomes a rotation handle - clicking and dragging rotates the selection
as opposed to moving it. I rotate the selection so that the bottom
edge is parallel to the horizon that I want level..... |
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| ..... before
dragging the rotated selection back across the image. |
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| Finally
I adjust the size of the selection by dragging the corner handles
in or out until the selection is completely contained within the
image area; |
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Once I'm happy with the selection angle and size, I'm
ready to commit to it.
Either a double-click within the selection area or clicking
on the Tick button in the tool bar will make the changes;
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| There we
are, a nice, level horizon - very reassuring for the residents of
the Isle of Wight downstream ;-) |
