ImageMagick Convert: how to add alpha shadows upon RGB image?

Question

Given a RGB image :

enter image description here

Given a grey scale, opacity 0% to opacity 100% black image:

enter image description here

How to add the alpha shadows upon the RGB image using a shell command ? (preferemce for ImageMagick Convert)

score 1 · Answer 1 · answered Apr 21 '14 at 15:13

I believe the example "Using Masks with Images" covers this. Simply disable the alpha channel, and copy over the second image as opacity composite. Add -negate option to invert the 0% ~ 100% opacity -- if needed.

 convert map_image.png elevation_mask.png \
         -alpha Off -compose CopyOpacity -composite \
         out.png

alpha mask

score 1 · Accepted Answer · answered Apr 29 '14 at 14:57

1

I would compose the images using the Multiply operator. The command

convert src.png overlay.png -compose Multiply -geometry 948x630 -composite out.png

produces:

enter image description here

answered Apr 29 '14 at 14:57

nwellnhof

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Given that both image have similar dimensions, is `-geometry 948x630` needed ? – Hugolpz Apr 29 '14 at 14:58
@Hugoplz They didn't have the same dimension when I downloaded them. If they have the same dimension the `-geometry` option is unnecessary. – nwellnhof Apr 29 '14 at 15:00
Oh, I may have upload one of the image AFTER resizing it, my apologizes. – Hugolpz Apr 29 '14 at 15:02

ImageMagick Convert: how to add alpha shadows upon RGB image?

2 Answers2