Crop geometry "center-north"

[baseballfury]

Hi,

I would like to batch convert images with different oriantations and resolutions. I want to resize and crop them to a square images with the same resolution.

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convert intput -resize "435x435^" -gravity center -crop 435x435+0+0 +repage output

I ran this code on the files, which gave me the expected results: a square image cropped around the center.
This is perfect for most pictures, but some images show a single person in portrait-format, where half the head gets cut off.

So I am looking for a mix of "geometry center" and "geometry north".




I have been using this php-function in the past to get the desired crop.

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//Portrait
$crop_y=($height_orig-$height_new)/6 //("/2" would center the image, "/6" turned out to be the optimal compromise)
imagecopyresampled($dst_img, $src_img, 0, 0, 0, $crop_y, 0, 435, 435, $width_orig, $height_orig)

Can I use Imagemagick alone to achieve this?

[snibgo]

Yes. You can either ask for "-gravity North" and start the crop somewhat lower, or "-gravity Center" and start the crop somewhat higher.

With IM v7, the arguments to "-crop" can be expressions, eg height/6. With IM v6, "-crop" can't use expressions, but viewports can.

[GeeMack]

So I am looking for a mix of "geometry center" and "geometry north". [...] Can I use Imagemagick alone to achieve this?

In concept, yes. There are several ways to approach this problem. As snibgo already mentioned, ImageMagic 7 can do all kinds of calculations within the command itself. But if you can't migrate/upgrade and you're using IM6, you can still use FX expressions, just in more limited ways. Here's a way to remove a calculated amount from the top of the image before cropping it to square...

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convert input.jpg -set page "+0-%[fx:h*0.166]" -crop +0+0 +repage ...

That would leave the lower 5/6 of the image to manipulate with the rest of your "-gravity" and "-crop" operations. Just replace the "..." with whatever you need to do from there.

[baseballfury]

Thank you. I will upgrade to ImageMagick 7.