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INTRODUCTION

Let's say I have this image:

enter image description here

To the image I apply the mask in https://image.ibb.co/c5Nw6c/Mask.png (it's white, that's why I set it here). The mask is basically a message bubble with an arrow in the bottom right part.

The command (in bash) is the following:

size=`convert Mask.png -format "%wx%h" info:`
convert \( couple.jpg  -channel rgba -alpha on -resize $size \) Mask.png -compose copy_opacity -composite -compose over -background transparent -flatten png:result.png

And the result is:

enter image description here

PROBLEM

Let's now check the next two images:

Image 2

enter image description here

Image 3

enter image description here

If we do the same with these two, we will obtain the following results:

enter image description here

enter image description here

What we see here is that in order for the mask to be applied correctly, the proportions must be similar, otherwise, depending on the original image's size, it might cropped in the bottom, or in the right.

QUESTION

How can I avoid the cropping problem and:

  1. Make the trimmed image (with respect to the mask) fill the whole mask without leaving any gaps and without losing proportions? I guess, by resizing, but how?
  2. Let the resized photo be centered (center of gravity) with respect to the mask?

Thank you very much for your answers.

juanba1984
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2 Answers2

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This command should take any input image then scale it to fill the mask. Next it composites the image centered over the mask with "srcin" to show just the part of the image where the mask is white. It finishes by flattening onto a white background. The output will be the dimensions of the mask.

convert Mask.png image.jpg \
   +distort SRT "0,0 %[fx:t?max(u.w/v.w,u.h/v.h):1] 0 0,0" \
   -shave 1x1 +repage -gravity center -compose srcin -composite \
   -compose over -background white -flatten result.png

This should work with IM 6.8.9 through IM 6.9.9.

GeeMack
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1

You are getting those results since the mask and the image have two different aspect ratios and sizes. You should resize the mask to conform exactly to the dimensions of the image rather than the other way around that you have done. So for example below, I have modified your Imagemagick command as follows:

enter image description here

infile="image.jpg"
size=`convert $infile -format "%wx%h" info:`
convert "$infile"  \( Mask.png -resize $size! \) -compose copy_opacity -composite -compose over -background transparent -flatten png:result.png

enter image description here

Note I add the ! to the -resize $size!, so that the mask is forced to fit the dimensions of the input.

EDIT: If you do not want to distort the mask, then the only way is to resize and pad the image to fill it to the size of the mask. Here I have changed the background from transparent to black to show the effect. You can change it back to transparent.

infile="image.jpg"
size=`convert mask.png -format "%wx%h" info:`
convert \
\( "$infile" -resize $size -background white -gravity center -extent $size \) \
Mask.png \
-compose copy_opacity -composite \
-compose over -background black -flatten \
png:result2.png

enter image description here

fmw42
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  • Useful answer, but adapting the mask to fit the source image will distort the mask. – juanba1984 Apr 08 '18 at 07:18
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    If you do not want to do that, then you have to pad the image after resizing to fit the mask. See my EDIT in my answer above. – fmw42 Apr 08 '18 at 18:33