Rotation

H
Posted By
humungus
Apr 4, 2006
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602
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11
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Closed
Hi
Does rotating an image a few degrees eg to straighten a horizon degrade an image? I cannot see how twisting square pixels say through 5 degrees cannot cause degradation regardless of what method is used to achieve the rotation? Any thoughts?
Hugh
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Andrew Morton
Apr 4, 2006
humungus wrote:
Does rotating an image a few degrees eg to straighten a horizon degrade an image? I cannot see how twisting square pixels say through 5 degrees cannot cause degradation regardless of what method is used to achieve the rotation? Any thoughts?

Yes, but if the result is satisfactory: who cares?

Andrew
GI
Glen in Orlando
Apr 4, 2006
why would it degrade a picture at all??
Each pixel is just that.. a pixel of light/color.
Each pixel can create ONE color right?
Rotate away… all you are doing, I believe, is changing the pixels location on the screen. You are NOT changing a "square pixel" into some sort of "skewed" pixel. A pixel is a pixel….
I really can’t see where you would get ANY degradation… JMHO
glen
2
2
Apr 4, 2006
"Glen in Orlando" wrote in message
why would it degrade a picture at all??
Each pixel is just that.. a pixel of light/color.
Each pixel can create ONE color right?

Pixels are not a single color. Pixels are not round dots. There are no spaces between pixels. Rotation can degrade, albeit not noticable if you work with a large enough image.

I really can’t see where you would get ANY degradation…

Clearly.
T
Tacit
Apr 4, 2006
In article ,
"humungus" wrote:

Does rotating an image a few degrees eg to straighten a horizon degrade an image?

Yes. The iage must be resampled for this to happen.

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T
Tacit
Apr 4, 2006
In article wrote:

Pixels are not a single color.

Yes, they are. One pixel is solid in color; a single pixel can not contain multiple colors.

A pixel is made up f channels, each of which carries a specific color information, but the total pixel is a single combination; you can not have one pixel that is yellow on one side and blue on the other.

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2
2
Apr 4, 2006
"tacit" wrote in message
In article wrote:

Pixels are not a single color.

Yes, they are. One pixel is solid in color; a single pixel can not contain multiple colors.

Sorry, Tacit; my poor English. I meant a pixel is not an elemental R,G,B,C, or M
Of course it is one color. It is one pixel!
H
humungus
Apr 5, 2006
Sure, I know a pixel stays sqaure but if for example a full white pixel is beside a full blackl pixel and you rotate 5 degrees – gien that a pixel is sqaure, it cannot reatina perfect vertical edge any longer sop soem degradation must happen?
N
nomail
Apr 5, 2006
Glen in Orlando wrote:

why would it degrade a picture at all??

Because you will resample the image doing so. Imagine you have a straight black line on a white background. Now rotate this a few degrees…

Rotate away… all you are doing, I believe, is changing the pixels location on the screen. You are NOT changing a "square pixel" into some sort of "skewed" pixel. A pixel is a pixel….

Wrong. Because pixels can indeed not be skewed, the image has to be resampled with any rotation other than 90 degrees, 180 degrees, or 270 degrees. Unless you rotate your monitor rather than the image?

I really can’t see where you would get ANY degradation…

I trust you can see it now.

—
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BV
Bart van der Wolf
Apr 5, 2006
"Johan W. Elzenga" wrote in message
Glen in Orlando wrote:

why would it degrade a picture at all??

Because you will resample the image doing so. Imagine you have a straight black line on a white background. Now rotate this a few degrees…
SNIP

Indeed, but the quality of the rotated image depends a lot the method used. Some methods retain information better than most built-in ones. Here are some examples of repeated rotation with significant differences in accumulated loss:
<http://photocreations.ca/interpolator/index.html>

Bart
H
humungus
Apr 6, 2006
I think that link makes the point perfectly – rotation other than through 90,180,270 is therefore to be avoided whenever possibnle in my opinion
Thanks
BV
Bart van der Wolf
Apr 6, 2006
"humungus" wrote in message
I think that link makes the point perfectly – rotation other than through 90,180,270 is therefore to be avoided whenever
possibnle in my opinion

Yes, although you have to recognize that those images have been rotated 5 degrees 36 separate/cumulative times.

A single rotation with a high quality interpolator (not Photoshop :-() won’t degrade the image visibly, but some loss is inevitable due to rounding errors in the calculations. It’s best avoided when taking the image, but the situation is not hopeless if e.g. a
rotation/perspective control is needed in postprocessing. Just use a quality tool/plug-in (and it’s free!).

Bart

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