Legacy ImageMagick Discussions Archive

Hello ImageMagic Community,
I'm here with a silly question, fore sure answered already somewhere, sorry for asking again, I cannot find a working solution.

I'm using the package ImageMagick-7.0.7-38-Q16-x64-dll.exe on a Win10Pro-x64.
I cannot manage to have -shave option to preserve original image aspect ratio.
I want to crop a border around the image of a certain number of pixels, I want to specify how may pixel to remove for width (or height) and I want ImageMagik to calculate how many pixel to remove for height (or width).

I'm using the following command line:
convert orig.jpg -shave 50 shaved.jpg
With an orig.jpg of 8920x3222, I always obtain a shaved.jpg = 8820x3122 which is a crop of -100x-100 which is not preserving the aspect ratio.
I would like to obtain either 8820x3186 (crop of -100x-36) or 8643x3122 (crop of -277x-100)
Whatever I've tried I always get the same crop for width and height which alter the aspect ratio.

I would appreciate your patient help.

Kinds Regards,
EFE.

You need to do inline computations of the aspect ratio and the amount to shave. Try these (Unix syntax for the variables)

Input:

Code: Select all

width=50
magick barn.jpg -format "%[fx:w/h]\n" info:
1.33779
magick barn.jpg -shave "${width}x%[fx:round($width*h/w)]" barn_aspect_shave.jpg
magick barn_aspect_shave.jpg -format "%[fx:w/h]\n" info:
1.33333

Code: Select all

height=50
magick barn.jpg -format "%[fx:w/h]\n" info:
1.33779
magick barn.jpg -shave "%[fx:round($height*w/h)]x${height}" barn_aspect_shave.jpg
magick barn_aspect_shave.jpg -format "%[fx:w/h]\n" info:
1.33668

Alternately, you can compute the crop width and height and use -gravity center -crop.

EFEIMCMNT wrote: ↑2018-06-08T15:01:37-07:00I cannot manage to have -shave option to preserve original image aspect ratio.
I want to crop a border around the image of a certain number of pixels, I want to specify how may pixel to remove for width (or height) and I want ImageMagik to calculate how many pixel to remove for height (or width).

As fmw42 mentioned, IM can calculate the necessary amount to remove using "-crop" or "-extent". Here are a couple examples. To shave 50 pixels from the left and right side, and shave the top and bottom as needed to maintain the original aspect, a command like this should work...

Code: Select all

set SHAVE=50
magick input.png -gravity center -extent "%[fx:w-(%SHAVE%*2)]x%[fx:h-((%SHAVE%*2)*h/w)]" result.png

If you want to specify shaving 50 pixels from the top and bottom, and calculate the amount to shave from the left and right, this command should work...

Code: Select all

set SHAVE=50
magick input.png -gravity center -extent "%[fx:w-((%SHAVE%*2)*w/h)]x%[fx:h-(%SHAVE%*2)]" result.png

To use these in a BAT script you need to change the single percent signs "%" on the FX expressions to doubles "%%".

"preserve-ratio" seems like a useful option to have on the shave command (or someplace similar).

Here is another approach using the new -crop ratio.

Code: Select all

xshave=50
yshave=0
magick input -set option:ratio "%w:%h" -shave "${xshave}x${yshave} -gravity center -crop "%[ratio]" +repage output

This command seems simple enough that I do not believe any new define is needed

Folks,
many thanks all ! I really appreciated your help on this.
You actually saved me a lot of time as I was going in the wrong direction.

Again many thanks for your patience in explaining things in very clear form.

Regards.

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