8 Rotating
My
camera has a handy level line on the screen. When I have time to use
it, I get lovely, level, horizon lines. If I'm in a hurry though, the
weight of my finger on the button often introduces a 1 degree tilt.
It
only really matters when it shows: When there's a horizon line or
conspicuously vertical or horizontal objects. Telegraph poles, flag
poles and brickwork are among the more common vertical features and
they really stand out if crooked..
Weirdly,
horizontal lines don't matter so much, unless its actually the
horizon line. This is because of 'perspective': that wonderful trick
that artists finally figured out in the renaissance. Look around you.
Horizontal lines either slope down or up, depending on whether
they're above or below eye level. Right now, I'm looking at skirting
boards and picture rails than make the point perfectly.
A
horizontal line is only horizontal at eye level (or exactly at right
angles to our line of sight), but a vertical line is always vertical.
Don't believe me? Go into the kitchen or bathroom and look at a tiled
wall.
It's
been pointed out to me that if you stand at the bottom of a tall
building and look up, the vertical lines seem to converge. That's
because you're line of sight has been reoriented from its normal,
horizontal plane to a vertical one. I am beset on all sides by
would-be smart-alecs.
Whether
or not you have a level line on your camera (or phone), you will
occasionally want to correct a crooked image. While your camera or
phone will have a rotate function of its own, it will probably only
work in 90 degree increments. That's fine for reorienting between
portrait and landscape format but doesn't solve the crooked picture
problem.
Photoshop
has an arbitrary rotating tool, which lets you turn an image
fractions of a degree clockwise or anti-clockwise. That's a cleverer
trick than you think. There is generally no noticeable loss in
quality when it rearranges all the pixels to accomplish this. The
maths behind it is mind-boggling so it's easiest just to accept that
it works beautifully.
In
this example, I've drawn a red level line so that you can see the
horizon isn't horizontal. It's clearly lower on the left.
It's
not much, but it'll annoy the heck out of you once you've noticed it
because you just can't unsee it. It'll leap out at you every time you
look at the picture. Trust me on that.
I
use the selection tool to test horizontal and vertical lines, just
because it's a convenient way to get a rectangle on the picture.
Anyway,
using the arbitrary rotating tool [image menu: rotate: arbitrary], I
turned the picture 1 degree clockwise. There's an element of trial
and error to this. If it's not enough, undo the action and try again.
DO NOT turn the same picture again and again as you will notice some
deterioration if you keep making Photoshop shuffle the pixels about.
Find the right amount then turn it in one go.
Now
the horizon is straight but the edges are obviously crooked. This is
a job for the Cropping tool.
The
more you've had to rotate the image, the more of the edge you'll lose
but it usually doesn't make a lot of difference, as in this case.
And
that's rotating. Simple really, but a technique well worth
remembering.