Image rotation relative to wrong (top right) point - imagemagick

Question

I am trying to place a rotated image onto a blank canvas.
This is the command i am using:
convert "(" -size 1000x1000 xc:transparent ")" "(" "img.jpg" -virtual-pixel white -rotate -10.75 ")" -geometry +136+148 -composite "overlay.png" -geometry +0+0 -composite out.png
I would expect the image to appear at +136+148 rotated around its center. However, it appears to be rotated around its upper right corner instead.
I confirmed this in Photoshop:
This is the resulting image (using slightly different size but same parameters as my example command given here):
The 4 lines are the guides that mark the coordinates that define where the image sits. As you can see, the image is rotated -10.75 degrees. And the rotation center is the upper right corner.
Here i select the box at the correct coordinates in Photoshop:
And here i rotate it after setting the rotation point to the top right:
As you can see, the selection now matches the image as it was calculated by my convert command.
I have tried dealing with this for many hours. I tried switching to +distort and -distort and what not, but there i simply get either a cropped image or another wrongly positioned bounding box.
I don't know how to address this problem. What am i doing wrong? How can i tell -rotate to rotate my image around its center, not around the top right corner (why top right anyway?).
Thank you for your help!

Answer 1

The default gravity for offsetting is the northwest corner or top-left corner. The geometry offset you are using moves the top left corner of the padded rotated image after its background has been added and not the top left corner of the where the Input gets rotated. So I think that may be why you are not getting the expected result. ImageMagick -rotate does rotate about its center, but it fills the background out to make a complete rectangular image that is the bounding rectangle about the rotated image.
In ImageMagick, a better approach to what you did would be to use -gravity center and align the center of the rotated input image with the center of the transparent region in the overlay image.
Alternately, measure the 4 corners of your transparent region in the overlay and 4 corners of the input image and do a perspective or affine distortion to align the two.
Here is how to do it in bash unix syntax.
over1="122,186"
over2="466,118"
over3="510,345"
over4="166,411"
WxH=`convert -ping "Image.jpg" -format "%wx%h" info:`
ww=`echo "$WxH" | cut -dx -f1`
hh=`echo "$WxH" | cut -dx -f2`
ww=$((ww-1))
hh=$((hh-1))
in1="0,0"
in2="$ww,0"
in3="$ww,$hh"
in4="0,$hh"
convert overlay.png \
\( Image.jpg -virtual-pixel none +distort Perspective \
"$in1 $over1 $in2 $over2 $in3 $over3 $in4 $over4" \) \
-layers merge +repage \
out.png
See https://imagemagick.org/Usage/distorts/#perspective

Answer 2

Try using the offset geometry that aligns with the outer edges of your target area. That would be more along the red lines I've added here, not along the cyan lines in your example image.
Edited to add: For a method of finding the proper offset information to fill the hole and placing the image under the hole, see my other answer in this thread.

Answer 3

You can find the location of the cutout in your overlay image, then use that information to properly place your under image with a command like this...
convert overlay.png -background none \
\( +clone -alpha extract -trim \
-set option:offset +%[fx:page.x]+%[fx:page.y] +delete \) \
\( image.jpg -rotate -10.7 -set page %[offset] \) \
-set page %[fx:u.w]x%[fx:u.h] +swap -layers merge result.png
This makes use of the fact that the bounding box dimensions of the rotated input image are the same as the bounding box dimensions of the cutout of the transparent region in the overlay image.
That reads in the overlay, and inside parentheses it makes a clone of it, extracts the alpha channel, and trims the result to find the offset of the cutout. It saves the offset to a variable named "offset".
Then inside another set of parentheses it reads in the under image, rotates it the known -10.7 degrees, and uses that variable "offset" to set the paging offset on the rotated "image.jpg".
Then outside the parentheses it uses the width and height of the overlay to set the paging dimensions for the under image.
It finishes by swapping the order of the images to put the overlay on top, then merging the two layers to create the output.

Answer 4

Here is an alternate to GeeMack's excellent ImageMagick solution. This computes the center of the original input.jpg, and the center of the transparent region in the Overlay.png. Then it uses +distort SRT to translate and rotate the image before finally compositing with -layers merge.
convert Overlay.png \
\( +clone -alpha extract -trim -set option:center "%[fx:page.x+w/2],%[fx:page.y+h/2]" +delete \) \
\( Image.jpg -virtual-pixel none +distort SRT "%[fx:w/2],%[fx:h/2] 1 -10.7 %[center]" \) \
+swap -layers merge +repage result2.png
The second line is much line GeeMack's, but it computes the center of the transparent region's bounding box and saves that in the "center" argument and then deletes the trimmed image.
The third line computes the center of the Input.jpg image (before rotation). It then uses +distort SRT to translate from the input center, (scale=1) and rotate -10.7 and translate to the center of the transparent region's bounding box.
See https://imagemagick.org/Usage/distorts/#srt