[Solved ]Rotating image.. won't stay centered

[Rye]

So, I tried rotating an image today.

This is my source:

[spoiler]

[/spoiler]

and after executing the following command:

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mogrify file.png -rotate 15 -background transparent file.png
convert file.png -crop 480x800+0+0 file.png

a few times, I got this:


[[EDIT: The animated gif image won't show correctly in the browser, I rar'd it up it shows correctly for me in irfanview: ]]
[[https://dl.dropboxusercontent.com/u/145 ... oating.rar]]

Not how I imagined it.
I probably need some approach to keep it centered. right ?
[Bonus points for whomever can figure out a way to make this script easier... like: execute once and output a user set numbers of roations aka 001. 002. 003. etc.)

Thanks in advance

[snibgo]

The ordinary "-rotate" will make the output large enough to hold the rotated input. So the output at 45 degrees will be bigger than at 0 degrees or 90 degrees. The problem isn't centering, but sizing.

One cure is to do an "-gravity Centre -extent" after each rotation, so it always enlarges to the same size.

[Rye]

Hmm...
ok, this looks good:

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for %%x in (*png) do mogrify -rotate 15 -background transparent %%x
for %%x in (*png) do convert %%x -gravity Center -crop 480x800-96-49 +repage  %%x

Too bad I have to do the math myself... wish imagemagick did this auto"magickally".

Can be tiresome if too many files are required


EDIT: NOPE, this still produces the strange moving of the picture (not centered).
What am I doing wrong ?

[Bonzo]

You have a -crop; snibgo suggested an -extent

[Rye]

Hmm...

using "-extent" instead of "-crop" yields me the same results.... the image spirals downwards...

for %%x in (*png) do mogrify -rotate 15 -background transparent %%x
for %%x in (*png) do convert %%x -gravity Center -extent 480x800+0+0 +repage %%x

[snibgo]

The only maths needed is to find the maximum space the image will occupy when rotated. The maximum space is a square, with sides equal to the diagonal of the image. Make the extent that size or larger.

For example, a Windows command to rotate the built-in "rose":

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for /L %i in (0,10,90) do convert rose: -rotate %i -gravity Center -extent 150x150 r_fr_%i.png

[snibgo]

"identify 001.gif" tells us the size of your image. It is 480x800 on a 941x1008 canvas. So extending this to 480x800 won't help.

The diagonal of 480x800 is 933. Call it 1000. So we can "-extent" to 1000x1000.

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for /L %i in (0,10,90) do convert 001.gif -rotate %i -gravity Center -extent 1000x1000 +repage r_fr_%i.png

It wobbles as it animates because the logo isn't centred in the image, "-trim" solves that problem.

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for /L %i in (0,10,90) do convert 001.gif -trim -rotate %i -gravity Center -extent 1000x1000 +repage r_fr_%i.png

[EDIT: I forgot to put "-trim" in the command.]

[Rye]

Ok, so this:

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move *.png source.png
for /L %%i in (0,10,90) do convert source.png -trim -rotate %%i -gravity Center -extent 1000x1000 +repage r_fr_%%i.png
for %%x in (*png) do convert %%x -gravity Center -extent 480x800+0+0 +repage  %%x

is pretty much perfect in execution !

The only question I now have left is:
How can I get this to create 12 frames "aka" 180° rotation ?

EDIT: I guess executing the script x2 and renaming the files did the trick.

Thanks

[snibgo]

My example rotated from 0 to 90 degrees, in steps of 10 degrees. You can change that to 0 to 180 degrees in steps of 15, or whatever you want.

[Rye]

Perfect ! Thanks.

Honestly this should be written into the imgmagck examples page.
(If it isn't already)